Vertebral Columns Spring 2025

Advancing the Assessment of Degenerative Change in the Cervical Spine The Impact of Lumbar Laterolisthesis on Degenerative Lumbar Surgery

Vertebral

COLUMNS International Society for the Advancement of Spine Surgery

Lumbar Pseudoarthrosis: Evaluation and Diagnostic Work-Up Is Segmental Plating a Superior Strategy for Multilevel ACDFs? The Clinical Significance of Segmental Lumbar Lordosis in Adjacent Segment Disease MILD Procedure: What Is the Evidence?

Do Spine Surgery Trainees Bring Value to Integrated Hospital Systems?

A Primer on Direct Care and Direct-to-Employer Contracting for Spine Surgeons

PLUS

Spine & Microbiome How Gut Health Affects Degenerative Disc Disease

SPRING 2025

IN THIS ISSUE:

Spring 2025

Editor in Chief Kern Singh, MD Editorial Board Brandon Hirsch, MD

EDITORIAL 3 Spine and Microbiome: How Gut Health Affects Degenerative Disc Disease

7 Advancing the Assessment of Degenerative Change in BONE HEALTH

the Cervical Spine

DEGENERATIVE DISEASE 13 The Impact of Lumbar Laterolisthesis on Degenerative Lumbar Surgery

23 Lumbar Pseudoarthrosis: Evaluation and Diagnostic COMPLICATIONS

Sravisht Iyer, MD Nathan J. Lee, MD Yu-Po Lee, MD Sheeraz Qureshi, MD, MBA Arash J. Sayari, MD Managing Editor Audrey Lusher Designer CavedwellerStudio.com

Work-Up

27 Is Segmental Plating a Superior Strategy for Multilevel BIOMECHANICS

Cover image generated by ChatGPT

ACDFs?

LUMBAR SPINE 30 The Clinical Significance of Segmental Lumbar Lordosis in Adjacent Segment Disease

LUMBAR SPINE 36 MILD Procedure: What Is the Evidence?

HEALTH CARE ECONOMICS 39 Do Spine Surgery Trainees Bring Value to Integrated Hospital Systems?

PRACTICE 45 ACLINICAL Primer on Direct Care and Direct-to-Employer Contracting for Spine Surgeons Spring 2025

Vertebral Columns

Vertebral Columns is published quarterly by the International Society for the Advancement of Spine Surgery. ©2025 ISASS. All rights reserved.

Opinions of authors and editors do not necessarily reflect positions taken by the Society.

This publication is available digitally at https://isass.org/category/news/ vertebral-columns/

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EDITORIAL

From the Department of Orthopaedic Surgery at Rush University Medical Center in Chicago, Illinois.

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Spine and Microbiome How Gut Health Affects Degenerative Disc Disease Many people are often surprised when realizing how interconnected the body is, and this is no exception for spine patients. Those with degenerative disc disease (DDD) may benefit from further research on how gut health affects this disorder. DDD is a chronic condition, and studies have shown that the disorder has a heavy contribution to lower back pain.1,2 The disease is severely painful for patients and can even impact their daily functions and quality of life.2,3 Moreover, there is minimal research in the field exploring how the gut is connected to the spine, which can contribute unique perspectives to patients struggling with chronic disorders. Studies have shown that modification of traditional treatment strategies is crucial for reducing the painful symptoms of DDD.4 The body’s gut microbiota (GM) communicates with parts of the spine, furthering the need for more research on the gut-spine connection to assist patients suffering from chronic spine disorders. Discoveries in this niche aspect of the field may offer vast improvements in patient quality of life, novel treatment plans, and increased patient-reported outcomes postoperatively.

What is Degenerative Disc Disease?

DDD may be present in different parts of the spine, such as the cervical or lumbar region. However, this condition is more common in those with lower back pain. DDD

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is fairly common, impacting 20% of adolescents and up to 50% of people aged 50 to 70 years.2 It is Shriya Patel, BS important to note that not all patients with DDD have symptoms.

Risk factors for this condition are herniated discs, smoking, high levels of physical labor, little to no physical activity, obesity, etc.2 Morevoer, genetics is also a risk Sloane Ward, BS factor for DDD as mutations in certain genes that encode for matrix molecules may alter the function and processes of the disc attributing to the disease.2 A study conducted by Sang et al showed around one-third of Kern Singh, MD patients with cervical DDD had anxiety or depression, and those who had severe symptoms were even more susceptible to inferior mental health. 5 Finding ways to alleviate symptoms associated with DDD may have a critical impact on patient mental health and quality of life.

The Role of the Gut Microbiome and Proper Nutrition The gut microbiome composition shifts throughout one's life based on various factors. Some factors include diet, exposure to the environment, geographical location, drugs and medications taken, and even aging.6 The function of the gut microbiome

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EDITORIAL

An artificial intelligence (AI) generated image of the interconnectedness of the spine and gut of the human body.

is to assist in destroying bacteria deemed damaging, monitor the immune system, and support digestion.7 A healthy gut contains anti-inflammatory microbes and maintains a stabilized microbiome composition.8 On the other hand, studies have shown that gut dysbiosis increases inflammation due to a leaky gut, where lipopolysaccharides are diffused into circulation.8 Moreover, nutritional disorders can also impact patients who have DDD, which can be viewed in relation to the aspects of the gut. Since the intervertebral discs are avascular, proper diffusion needs to occur with nutrients and gases passing through the matrix to reach the cells. 2 If

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there are nutritional disorders, this diffusion may not occur appropriately and can lead to degenerative diseases, which would make a patient more susceptible if they also have poor gut health.

Li et al hypothesized the mechanisms by which the gut microbiota can cause intervertebral disc disease, such as the transfer of bacteria across the epithelial barrier of the gut into the intervertebral disc and the irregular production of pro-inf lammatory factors by intervertebral disc cells and immune cells. 9 Inter vertebral discs are protected by a barrier to keep out bacteria, which can induce inflammatory processes.

However, this barrier around intervertebral discs can also block immune cells that are critical for recognizing and eliminating harmful elements.9 Due to intestinal inflammation, bacteria can begin to translocate from the epithelial layer of the gut into the intervertebral disc.9 Immune cells may not be able to receive timely feedback from the microenvironment of the disc, resulting in an adverse inflammatory reaction at the disc. 9 The body’s reaction to bacterial invasion is the secretion of inflammatory cytokines such as IL-1α/β, IL-17, TNF-α, and IL-6, which can disrupt the matrix of the intervertebral disc by degrading collagen production.9 Essentially, this chain of reactions provokes chemokine production that further deteriorates the extracellular matrix around an intervertebral disc. 9 Therefore, DDD arises from the amplification of inf lammatory processes, specifically from the activation of macrophages, B cells, T cells, and neutrophils from the damaged intervertebral disc.9

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EDITORIAL

Dietary Intervention for a Healthy Gut and Spine Considering the effects of gut dysbiosis resulting in DDD, it is imperative to maintain a healthy gut microbiome. In particular, diet is a major contributor to the composition of the gut microbiome.10 Rinninella et al studied the effects of a typical Western diet, consisting of elevated levels of saturated fats, refined sugars, and processed foods, and found that this diet resulted in increased levels of bacterial species that correlate with dysbiosis and disease, such as Firmicutes.10 In contrast, a Mediterranean diet based on regular fiber intake consisting of whole grains, vegetables, fruits, and legumes was associated with a lower Firmicutes-to-Bacteroidetes ratio and a higher level of short-chain fatty acids.10 These findings are particularly relevant for individuals with back pain and degenerative disc conditions, as short-chain fatty acids promote the differentiation of primary CD4++ cells into regulatory T cells that play a role in regulating inflammation.11 Regulatory T cells suppress extreme immune responses to prevent chronic inflammation, which can result in DDD. In particular, regulatory T cells are essential in bone formation as they are located on the endosteal surface and promote osteoblast differentiation while inhibiting osteoclast formation.11 Additionally, bone formation is controlled by regulatory T cells through managing the activity of the parathyroid hormone, which balances calcium and bone metabolism to stimulate bone formation.11 Therefore, it is important to include short-chain fatty acids in one’s diet to maintain bone health and prevent disc degeneration through a leaky gut permeating bacteria and resulting in inflammatory

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responses. In a study conducted by Rajasekaran et al, 40 patients with disc degeneration were studied, and it was found that short-chain fatty acid-producing bacteria were significantly lower in these individuals in comparison to the healthy volunteers.12 On the other hand, patients who did have disc degeneration had a decreased Firmicutes-to-Bacteroidetes ratio compared to healthy individuals.12 Therefore, further studies are warranted to determine the impact of balancing gut microbiomes based on whether they have harmful or beneficial properties.

Additionally, Ratna et al illustrated that the administration of probiotics can shift inflammatory molecules, such as interleukin (IL) -1, -2, -4, -6, and tumor necrosis factor alpha (TNF-α) into an anti-inf lammatory state, which includes markers such as IL-10 and transforming growth factor-beta (TGF-β).13 This finding demonstrates that taking probiotics can be beneficial to reduce inflammation in the spine and potentially slow intervertebral disc degeneration through non-inflammatory mechanisms.

Future Research and Potential Treatments Current strides are being made in determining the connection between the gut microbiota and the spine. For instance, Yao et al studied the efficacy of fecal microbiota transplantation in rats.14 Elevated levels of inflammatory markers such as TNF-α and IL-6 were found in rats with intervertebral DDD using an enzyme-linked immunosorbent assay.14 Ultimately, fecal microbiota transplantation was shown to inhibit the elevated levels of inflammatory molecules

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in the rats with intervertebral DDD while also upregulating collagen II expression and restoring the homeostasis in the gut microbiota to gradually show improvements in the mice with degenerative discs.14 Collagen II expression is crucial to prevent disc degeneration as it is a major component of the extracellular matrix, providing strength and structure.14 The study highlights the efficacy of treatment for mice, and future studies should explore the effect of fecal microbiota implementation in humans.

Conclusion Ultimately, prior studies connecting the mechanisms of gut health and DDD illustrate that the gut plays a pivotal role in influencing even distant areas of the body. Therefore, it is important to maintain a healthy diet to supplement the gut microbiota with beneficial bacteria and ensure that the microbiome is balanced.

The disruption of the delicate balance of the gut microbiota can result in adverse effects, such as the translocation of bacteria across the barrier of the spine to the avascular intervertebral disc, where inflammatory processes occur and contribute to pain. Additionally, it is imperative to maintain healthy short-chain fatty acid levels to regulate inflammation and parathyroid hormone activity. Existing studies have paved the way for forthcoming research that can be valuable to establish personalized probiotic treatment plans for individuals to obtain the microbiota they need to keep their bones healthy. Advancements such as 16S rRNA sequencing to determine commensal levels and fecal microbiota are considerable strides to unveiling the future of treatments starting from the gut to potentially slow the degeneration of disks and reduce the need for surgical intervention.14 l

References 1. Kirnaz S, Singh S, Capadona C, et al. Innovative biological treatment methods for degenerative disc disease.

World Neurosurg. 2022;157:282-299.

2. Kos N, Gradisnik L, Velnar T. A brief review of the degenerative intervertebral disc disease. Med Arch. 2019;73(6):421-424.

3. Battié MC, Joshi AB, Gibbons LE; ISSLS Degenerative Spinal Phenotypes Group. Degenerative disc disease: what is in a Name?. Spine (Phila Pa 1976). 2019;44(21):1523-1529.

4. Morimoto T, Kobayashi T, Kakiuchi T, et al. Gut-spine axis: a possible correlation between gut microbiota and spinal degenerative diseases.

Front Microbiol. 2023;14:1290858.

5. Sang D, Xiao B, Rong T, et al. Depression and anxiety in cervical degenerative disc disease: who are susceptible?

Front Public Health. 2023;10:1002837.

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6. Bradley E, Haran J. The human gut microbiome and aging. Gut Microbes. 2024;16(1):2359677.

7. Jandhyala SM, Talukdar R, Subramanyam C, Vuyyuru H, Sasikala M, Nageshwar Reddy D. Role of the normal gut microbiota. World J Gastroenterol. 2015;21(29):8787-8803.

8. Mousa WK, Chehadeh F, Husband S. Microbial dysbiosis in the gut drives systemic autoimmune diseases.

Front Immunol. 2022;13:906258.

9. Li W, Lai K, Chopra N, Zheng Z, Das A, Diwan AD. Gut-disc axis: a cause of intervertebral disc degeneration and low back pain? Eur Spine J. 2022;31(4):917-925.

10. Rinninella E, Tohumcu E, Raoul P, et al. The role of diet in shaping human gut microbiota. Best Pract Res Clin Gastroenterol. 2023;62-63:101828.

11. Wang K, Liu X, Huang H, et al. A new target for treating intervertebral disk degeneration: gut microbes.

Front Microbiol. 2024;15:1452774.

12. Rajasekaran S, Vasudevan G, Tangavel C, et al. Does the gut microbiome influence disc health and disease? The interplay between dysbiosis, pathobionts, and disc inflammation: a pilot study. Spine J. 2024;24(10):1952-1963.

13. Ratna HVK, Jeyaraman M, Yadav S, Jeyaraman N, Nallakumarasamy A. Is dysbiotic gut the cause of low back pain? Cureus. 2023;15(7):e42496.

14. Yao B, Cai Y, Wang W, et al. The effect of gut microbiota on the progression of intervertebral disc degeneration.

Orthop Surg. 2023;15(3):858-867.

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From the 1Department of Spine Surgery at the Hospital for Special Surgery in New York, New York, and 2Weill Cornell Medical College in New York, New York.

BONE HEALTH

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Advancing the Assessment of Degenerative Change in the Cervical Spine Degenerative cervical spine disease (cer v ical spondylosis) is a form of osteoarthritis that affects the spine, characterized by the spontaneous degeneration of either the disc or facet joints, leading to axial neck pain and neurological complications that may require surgical intervention (Figure 1). Research on the Medicare Claims 5% Limited Data Set found that the average prevalence of spinal degeneration was 27.3% ± 1.7%.1 While the spine undergoes age-related degenerative changes that are nearly universal, they can begin as early as the first decade of life. 2 Popu lat ion-based st udies indicate that roughly 80% to 90% of individuals exhibit disk degeneration on magnetic resonance imaging (MRI) by age 50 years.3,4 Due to the increasing prevalence of degenerative changes in the cervical spine among the aging US population,5 it is essential to diagnose and treat this condition appropriately.

This review will examine current methods for assessing degenerative changes in the cervical spine and highlight the necessity of enhancing the diagnosis of related conditions more effectively.

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Clinical Presentation of Degenerative Changes in the Cervical Spine Cervical spondylosis is caused by various degeneration processes, including aging, overuse, and trauma. While it can affect bone quality and joint structures, the most common changes primarily occur in the intervertebral disks and facet joints.6,7 With aging, the intervertebral disc undergoes degenerative changes characterized by the depletion of nucleus pulposus cells, which are responsible for maintaining the proteoglycan-rich extracellular matrix. Concurrently, the cartilaginous endplates become sclerotic, impairing nutrient diffusion into the disc. These processes lead to disc desiccation and progressive reduction in disc height.

When disc space narrowing becomes severe, the normally aneural annulus fibrosus may undergo neo-innervation, contributing to nociceptive signaling.

Additionally, marginal osteophy te formation can occur similar to that seen in other synovial joints under mechanical stress. The facet joints, which primarily function to limit axial

Atahan Durbas, MD1

Courtney S. Harris, BA2

Sophie C. Kush, BS2

Tomoyuki Asada, MD, PhD1

Sheeraz Qureshi, MD1

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Figure 1. Bilateral cervical spine x-rays demonstrate degenerative changes consistent with cervical spondylosis, including disc space narrowing and osteophyte formation.

rotation and sagittal plane motion, subsequently bear increased mechanical loading due to the loss of disc height. This increased axial stress accelerates the degeneration of facet joints.7–9 These structural changes can lead to a range of clinical manifestations.

Patients with degenerative cervical spondylosis might show signs of mechanical neck pain, radiculopathy, myelopathy, or a mix of these symptoms.

Neck pain is quite common, impacting about 15% of the general population at any given time.10 Mechanical neck pain may stem from signals from intervertebral joint receptors, where abnormal nerve fibers are proliferating. These signals are communicated primarily to the cervical paraspinal muscles, leading to muscle spasms and resulting in typical interscapular and lateral neck pain.11 Cervical spondylotic radiculopathy (CSR) occurs when a nerve exiting the spinal cord is compressed. This compression can arise from a degenerated disc, such as a herniated disc, where a weak spot in the annulus allows

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the inner disc material to press against the nerve root. It can also result from foraminal stenosis narrowing caused by bone spur or hypertrophied ligamentum f lavum on moderate to severe degenerative facet or intervertebral joint.12 Degenerative cervical myelopathy (DCM) typically involves severe disc and facet degeneration, resulting a narrowed spinal canal and subsequent deformation of the spinal cord.13 These results in DCM are also commonly secondary to disc herniation, with the C7 root being the most frequently affected, followed by C6 and C8.14,15

Current Assessment Methods Clinical evaluation is important for assessing degenerative cervical spine disorders and depends primarily on patient history, symptom description, physical examination, and patient-reported outcome measures.

Neurological symptoms in extremities, including CSR and DCM, often necessitate detailed radiographic assessments. This typically includes anteroposterior, lateral, and oblique x-ray images, which are economical and provide information on degenerative changes and alignment,16,17 potentially showing a reduction in normal cervical lordosis, hypertrophic changes, and narrowing of the disc space. Lateral flexion or extension views may also disclose ankylosed segments, cervical instability, limited range of motion, and fused cervical spine segments.6,18 Most flexion and extension motions of the cervical spine come from C4-C6. It is most common to see the earliest and considerable degenerative changes at the C5-C6 segment.19

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In contrast, a challenge when assessing patients with only neck pain is that nearly all individuals older than 50 years show degenerative cervical changes on radiographic imaging, often without specific findings. 3,4 Degenerative changes such as the narrowing of the intervertebral disc space, facet and uncovertebral joint osteoarthrosis, the presence of osteophytes, and end-plate sclerosis are common among adult patients and are not diagnostic.17,20 Thus, diagnostic imaging is recommended for selected patients experiencing ongoing neck, shoulder, or arm pain that either does not respond to standard conservative treatment or occurs with suspected neurological symptoms.6,11,21 In contrast, diagnostic images is often not recommended for patients presenting with nontraumatic neck pain without neurologic symptoms, signs, or red flags for malignancy.

Cervical spine MRI without contrast is the preferred imaging method for patients with progressive neurologic impairments or signs of myelopathy, as it offers insights into osseous structures, soft tissues, and spinal cord structures.22 It is also indicated for neck pain in patients with a history of malignancy, prior cervical surgery, or suspected infection.21 It often shows abnormalities, making it essential to correlate these imaging results with clinical findings. 23 If an MRI cannot be performed or is not accessible, a CT scan or CT myelography of the cervical spine should be considered.

Compressive osteophytes, foraminal stenosis, and ossification of the posterior longitudinal ligament are most effectively detected using CT scans. Additionally, CT myelography,

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which is an invasive procedure, is said to outperform MRI in differentiating between osseous and soft-tissue compressions of neural structures, as well as in identifying foraminal stenosis. 24,25 Current cervical disc degeneration assessment employs both qualitative and quantitative methods, each with distinct strengths. The Pfirrmann classification (grades I-V), initially developed for the lumbar spine, remains widely used in cervical evaluations due to its familiarity. This classification evaluates disc structure, signal intensity, and height loss on T2-weighted MRI, demonstrating almost perfect intraobserver reliability (κ = 0.858) but only fair interobserver agreement (κ = 0.265). 26,27 In contrast, the Suzuki classification (grades 0-III), designed specifically for cervical discs, provides a more accurate representation of cervical pathology and a more even grade distribution, although its interobser ver reliability is similarly modest (κ = 0.29).27,28 Both systems cluster most cases into midgrade categories (Pfirrmann III-IV, Suzuki II), which limits their sensitivity to early changes. 29 Meanwhile, Kettler and Wilke’s review 26 highlights reliability challenges across 42 spine degeneration systems, recommending Pfirrmann and Suzuki for discs (κ >0.6) while advocating for standardized scales starting at grade 0 for normal anatomy.

Kellgren and Lawrence et al 30 focused on osteophytes and disc narrowing, but their study lacked sensitivity for early degeneration, limiting its utility compared to MRI’s soft-tissue detail. Using CT, Huang et al 31

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adapted the Kellgren and Lawrence system to assess uncovertebral joint degeneration, grading changes from normal (Grade 0) to joint fusion or severe osteophyte articulation (Grade 4). Facet joint degeneration is best evaluated by CT, as exemplified by Park et al’s grading system (grades I–IV), which identifies the upper cervical levels (C2/3–C4/5) as degeneration-prone with high reliability (ICC = 0.87–0.89). 32 Emerging quantitative tools, such as the Disc Signal Intensity Index (DSI2), address subjectivity limitations by normalizing the disc T2 signal to cerebrospinal fluid, achieving superior interobserver reliability (ICC = 0.90). 33 DSI2 correlates linearly with Pfirrmann grades but detects early degeneration that is missed by qualitative systems and identifies novel associations (eg, diabetes is linked to higher DSI2, possibly due to metformin’s protective effects).33 Large-scale MRI studies 28 validate that degeneration begins at C5/6, progresses contiguously, and rarely skips levels—critical for understanding adjacent-segment disease. While qualitative systems remain clinically practical, DSI2 and similar metrics show promise for research requiring precision, particularly in tracking subtle degenerative changes and evaluating therapeutic interventions.

Advancements in Diagnostic Tools New imaging modalities are improv ing diagnostic precision by providing more detailed, functionally relevant information.

Dynamic MRI enhances the detection of motion-dependent foraminal and canal narrowing, which may be missed on static

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imaging.34 In preoperative patients, dynamic MRI identified occult stenosis in nearly half of the cases, 34 leading to improved surgical planning and postoperative outcomes. 35,36 Although it is useful, issues with motion artifacts and acquisition duration have hindered broader adoption.

Building on these imaging advancements, artif icial intelligence (AI), particularly deep learning (DL) models, are becoming increasingly used to predict outcomes after cervical spine surgery. Expanding upon these diagnostic capabilities, AI systems are progressively evolving from primarily focusing on diagnosis to actively supporting clinical decision-making. New DL models have been developed for MRI-based clinical decision support, specifically for degenerative cervical spine disorders, aiming to evaluate alignment with treatment recommendations from experienced spine specialists. 37 Three-dimensional (3D) Deep Learning–Enhanced MRI (3D-DLRecon) enhances the visualization of foraminal stenosis and bony detail with high-resolution, multiplanar reconstructions. 38 It provides better diagnostic reliability than standard two-dimensional (2D) sequences and could be helpful for preoperative assessment of disc space narrowing and facet degeneration. 39 Beyond structural imaging, novel techniques are also emerging to evaluate early biochemical and mechanical changes in the cervical spine. T1ρ MRI, which is sensitive to proteoglycan depletion, has demonstrated utility in detecting early disc degeneration before morphological changes appear. 40 DualMRI, which quantifies voxel-level strain

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under physiological loading, may offer a noninvasive mechano-biomarker of disc health and treatment response.41 18F-NaF PET/CT, a metabolic imaging modality, has demonstrated uptake in vertebral and facet joints that correlates with age-related degeneration, suggesting its potential use as a biomarker for disease activity and progression.42 Finally, genomic and epigenetic profiling represent a promising frontier for risk stratification in DCM. While no genome-wide significant SNPs were identified, variants in genes such as COL6A1, APOE, and RUNX2, along with nongenetic risk factors, including age, sex, and socioeconomic status, have been implicated in DCM susceptibility.43

Clinical Implications and Future Directions With the growing incidence of degenerative cervical spine disease due to an aging population, the importance of timely and precise diagnosis, as well as tailored manage-

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ment strategies, is becoming more critical.

Traditional assessment methods remain foundational but are often limited by nonspecific findings and a lack of correlation with symptom severity. The combination of advanced imaging techniques, including dynamic MRI, 3D-DLRecon, and PET/CT, along with cutting-edge technologies such as AI applications and genomic profiling, signifies a pivotal advancement toward precision medicine in cervical spine care.

These innovations enable earlier detection of pathology, provide enhanced clinical care, and facilitate superior risk stratification for patients with complex presentations. Moving forward, collaboration across disciplines and ongoing research into AI-driven diagnostics, molecular biomarkers, and imaging-based mechano-biomarkers will be valuable assets for enhancing patient outcomes and creating a more proactive, personalized strategy for managing degenerative cervical spine disorders. l

References 1. Parenteau CS, Lau EC, Campbell IC, Courtney A. Prevalence of spine degeneration diagnosis by type, age, gender, and obesity using Medicare data. Sci Rep. 2021;11(1):5389.

4. Brinjikji W, Luetmer PH, Comstock B, et al. Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. Am J Neuroradiol. 2015;36(4):811-816.

2. Benoist M. Natural history of the aging spine. Eur Spine J. 2003;12(0):S86-S89.

5. Oglesby M, Fineberg SJ, Patel AA, Pelton MA, Singh K. Epidemiological trends in cervical spine surgery for degenerative diseases between 2002 and 2009. Spine. 2013;38(14):1226-1232.

3. Teraguchi M, Yoshimura N, Hashizume H, et al. Prevalence and distribution of intervertebral disc degeneration over the entire spine in a population-based cohort: the Wakayama Spine Study. Osteoarthritis Cartilage. 2014;22(1):104-110.

6. Rao RD, Currier BL, Albert TJ, et al. Degenerative cervical spondylosis: clinical syndromes, pathogenesis, and management. Instr Course Lect. 2008;57:447-469.

7. Theodore N. Degenerative cervical spondylosis [review]. N Engl J Med. 2020;383(2):159-168.

8. Van Der Werf M, Lezuo P, Maissen O, Van Donkelaar CC, Ito K. Inhibition of vertebral endplate perfusion results in decreased intervertebral disc intranuclear diffusive transport. J Anat. 2007;211(6):769-774.

9. Feng C, Liu H, Yang M, Zhang Y, Huang B, Zhou Y. Disc cell senescence in intervertebral disc degeneration: causes and molecular pathways.

Cell Cycle. 2016;15(13):1674-1684.

References continued on page 12

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10. Voorhies RM. Cervical spondylosis: recognition, differential diagnosis, and management.

Ochsner J. 2001;3(2)78-84.

11. Binder AI. Cervical spondylosis and neck pain. BMJ. 2007;334(7592):527-531.

12. Bono CM, Ghiselli G, Gilbert TJ, et al.

An evidence-based clinical guideline for the diagnosis and treatment of cervical radiculopathy from degenerative disorders. Spine J. 2011;11(1):64-72.

13. Williams J, D’Amore P, Redlich N, et al.

Degenerative Cervical Myelopathy. Orthop Clin North Am. 2022;53(4):509-521.

14. Montgomery DM, Brower RS. Cervical spondylotic myelopathy. Clinical syndrome and natural history. Orthop Clin North Am. 1992;23(3):487-493.

15. Iyer S, Kim HJ. Cervical radiculopathy. Curr Rev Musculoskelet Med. 2016;9(3):272-280.

16. Green C, Butler J, Eustace S, Poynton A, O’Byrne JM. Imaging modalities for cervical spondylotic stenosis and myelopathy. Adv Orthop. 2012;2012:1-4.

17. Gore DR, Sepic SB, Gardner GM. Roentgenographic findings of the cervical spine in asymptomatic people. Spine. 1986;11(6):521-524.

18. White AA 3rd, Panjabi MM. Update on the evaluation of instability of the lower cervical spine. Instr Course Lect. 1987;36:513-520.

19. Holmes A, Wang C, Han ZH, Dang GT. The range and nature of flexion-extension motion in the cervical spine.

Spine. 1994;19(22):2505-2510.

20. Gore DR. Roentgenographic findings in the cervical spine in asymptomatic persons: a ten-year follow-up.

Spine. 2001;26(22):2463-2466.

21. McDonald MA, Kirsch CFE, Amin BY, et al. ACR Appropriateness Criteria® cervical neck pain or cervical radiculopathy. J Am Coll Radiol. 2019;16(5):S57-S76.

22. Nouri A, Martin AR, Mikulis D, Fehlings MG. Magnetic resonance imaging assessment of degenerative cervical myelopathy: a review of structural changes and measurement techniques.

Neurosurg Focus. 2016;40(6):E5.

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23. Teresi LM, Lufkin RB, Reicher MA, et al. Asymptomatic degenerative disk disease and spondylosis of the cervical spine: MR imaging.

Radiology. 1987;164(1):83-88.

24. Jahnke RW, Hart BL. Cervical stenosis, spondylosis, and herniated disc disease. Radiol Clin North Am. 1991;29(4):777-791.

25. Shafaie FF, Wippold FJ 2nd, Gado M, Pilgram TK, Riew KD. Comparison of computed tomography myelography and magnetic resonance imaging in the evaluation of cervical spondylotic myelopathy and radiculopathy.

Spine. 1999;24(17):1781-1785.

26. Kettler A, Wilke HJ. Review of existing grading systems for cervical or lumbar disc and facet joint degeneration.

Eur Spine J. 2006;15(6):705-718.

27. Urbanschitz L, Bensler S, Merat S, Lenz CG, Eid K. How should we grade cervical disk degeneration? a comparison of two popular classification systems.

Spine Surg Relat Res. 2021;5(6):347-351.

28. Suzuki A, Daubs MD, Hayashi T, et al.

Patterns of cervical disc degeneration: analysis of magnetic resonance imaging of over 1000 symptomatic subjects.

Glob Spine J. 2018;8(3):254-259.

29. Mesregah MK, Repajic M, Mgbam P, Fresquez Z, Wang JC, Buser Z. Trends and patterns of cervical degenerative disc disease: an analysis of magnetic resonance imaging of 1300 symptomatic patients. Eur Spine J. 2022;31(10):2675-2683.

30. Kellgren JH, Lawrence JS. Radiological assessment of osteo-arthrosis.

Ann Rheum Dis. 1957;16(4):494-502.

31. Huang T, Qin J, Zhong W, Tang K, Quan Z. The CT assessment of uncovertebral joints degeneration in a healthy population. Eur J Med Res. 2021;26(1):145.

32. Park MS, Lee YB, Moon SH, et al.

Facet joint degeneration of the cervical spine: a computed tomographic analysis of 320 patients.

Spine. 2014;39(12):E713-E718.

33. Tsuchiya K, Okano I, Guven AE, et al. Quantitative assessment of cervical disc degeneration using disc signal intensity index.

Spine J. 2025;25(5):903-910.

34. Şerifoğlu L, Karaaslanlı A. The role of dynamic cervical magnetic resonance imaging in determining the level of posterior decompression in cervical spondylotic myelopathy.

World Neurosurg. 2025;195:123698.

35. Zhang JK, Yakdan S, Kaleem MI, et al.

Spinal cord metrics derived from diffusion MRI: improvement in prognostication in cervical spondylotic myelopathy compared with conventional MRI. J Neurosurg Spine. 2024;41(5):639-647.

36. Berberat J, Andereggen L, Gruber P, Hausmann O, Reza Fathi A, Remonda L. A diagnostic biomarker for cervical myelopathy based on dynamic magnetic resonance imaging. Spine. 2023;48(15):1041-1046.

37. Li KY, Lu ZY, Tian YH, et al. Deep learning models for MRI-based clinical decision support in cervical spine degenerative diseases.

Front Neurosci. 2024;18:1501972.

38. Almansour H, Herrmann J, Gassenmaier S, et al. Deep learning reconstruction for accelerated spine MRI: prospective analysis of interchangeability.

Radiology. 2023;306(3):e212922.

39. Jardon M, Tan ET, Chazen JL, et al. Deep-learning-reconstructed high-resolution 3D cervical spine MRI for foraminal stenosis evaluation.

Skeletal Radiol. 2023;52(4):725-732.

40. Johannessen W, Auerbach JD, Wheaton AJ, et al. Assessment of human disc degeneration and proteoglycan content using T1-weighted magnetic resonance imaging. Spine (Phila Pa 1976). 2006;31(11)1253-1257.

41. Wilson RL, Bowen L, Kim W, et al. In vivo intervertebral disc deformation: intratissue strain patterns within adjacent discs during flexion–extension. Sci Rep. 2021;11(1):729.

42. Park PSU, Raynor WY, Khurana N, et al. Application of 18F-NaF-PET/ CT in assessing age-related changes in the cervical spine. Quant Imaging Med Surg. 2022;12(6):3314-3324.

43. Shlykov MA, Giles EM, Kelly MP, et al. Evaluation of genetic and nongenetic risk factors for degenerative cervical myelopathy. Spine.

2023;48(16):1117-1126. doi:10.1097/ BRS.0000000000004735

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From the 1Department of Orthopaedics at the Hospital for Special Surgery in New York City, New York; 2Weill Cornell Medical College in New York City, New York; and 3Department of Orthopedics at the University of Tsukuba Hospital in Tsukuba, Japan.

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The Impact of Lumbar Laterolisthesis on Degenerative Lumbar Surgery Lumbar laterolisthesis (or lateral spondylolisthesis) is the lateral displacement of one vertebra relative to the vertebra below it, commonly resulting from degenerative changes. An estimated 10% of patients exhibit radiographic evidence of laterolisthesis.1 The prevalence of laterolisthesis is highly influenced by factors such as age, sex, and the presence of other degenerative spinal conditions. For instance, it is significantly more common in women, and its prevalence increases gradually with age.1 It often presents as a triaxial defect due to the combination of axial rotation and anterior translation.2 Laterolisthesis is significantly more common in individuals with scoliosis, occurring in 13% to 20% of adults with scoliosis.1–4 Its multidimensional and multifactorial pathophysiology can present with variable symptomology and poses greater variability in surgical management compared to anterolisthesis, increasing the complexity of diagnosis and management. 5 Despite its clinical relevance, degenerative lumbar laterolisthesis remains an underrepresented topic in literature. Its role in degenerative spinal pathology is substantial, yet it is not

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widely recognized as a major contributor to spinal instability and surgical complexity. Greater focus is needed in research and clinical practice, as it complicates degenerative lumbar surgery and can impact patient outcomes. Therefore, this article reviews the current evidence on the clinical impact of lumbar laterolisthesis on degenerative lumbar surgery.

Pathophysiology of Lumbar Laterolisthesis Biomechanical and Structural Contributors Lumbar laterolisthesis results from a complex interplay of biomechanical and structural changes in the spine that lead to segmental instability and progressive spinal misalignment, 6 causing biomechanical pathology in the spine. A key biomechanical factor is disc degeneration, which results in the loss of disc height and disrupts the normal load-bearing capacity of the spinal column.7 Loss of disc height permits increased segmental motion, allowing lateral translation of vertebral segments.8 Asymmetrical disc degeneration further exacerbates instability, as one side of the vertebra experiences

Adrian Lui, MBBS1

Amy Z. Lu, BS1,2

Tarek Harhash, BS1

Tomoyuki Asada, MD PhD1,3

Sravisht Iyer, MD1

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greater collapse, promoting lateral displacement.6 Facet joint degeneration also plays a role in laterolisthesis. 9 Normally, the facet joints guide and restrict spinal movement, resisting excessive shearing forces. 9 However, the occurrence of asymmetric facet joint arthropathy reduces resistance to lateral translation, allowing for progressive displacement. 9 Additionally, ligamentous laxit y contributes to spinal instabilit y.10 The intertransverse ligaments, which limit lateral bending, and the interspinous ligaments, which help stabilize the posterior column, progressively weaken due to chronic stress and degeneration. This laxity allows increased motion at the affected segment, especially when combined with asymmetric disc and facet degeneration.10 The interplay of these factors was further demonstrated in a seminal biomechanical study by Okushima et al, who conducted an in vitro study on whole lumbar cadaveric spines under multidirectional loading.11 Their results demonstrated that force applied in the anterolateral direction produced greater lateral translation than force in the posterolateral direction, suggesting that specific vectors of load may disproportionately destabilize the lumbar spine. Moreover, they found that the removal of the facet joints at L4-L5 resulted in significantly more lateral translation than the removal of the intervertebral discs under shear loading conditions, highlighting the critical role of facet joints in resisting translational instability. These findings provide key insights into the pathogenesis of laterolisthesis, emphasizing that while disc degeneration facilitates abnormal

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motion, progressive facet joint degeneration plays a primary role in destabilizing the spine and allowing for pathological lateral vertebral translation, particularly at vulnerable lumbar segments.

Association With Spinal Malalignment The biomechanics of lateral vertebral translation may be highly interlinked with the pathophysiology of scoliosis, though the causative relationship remains speculative.4 Asymmetric degeneration in intervertebral discs and facet joints predisposes the spine to lateral vertebral translation and excessive curvature of the spine while the resulting coronal malalignment further accelerates degenerative changes.4 Toyone et al described a correlation between vertebral translation and rotation, demonstrating that in patients with both laterolisthesis and scoliosis, cephalad vertebrae rotated toward the convex side of the primary scoliotic curve while caudal vertebrae rotated toward the convex side of the lumbosacral hemi-curve.4 These findings reinforce the 3-dimensional complexity of laterolisthesis.

Additionally, Kilshaw et al found that laterolisthesis was significantly more prevalent in patients with scoliosis (44.0% vs 3.8%), suggesting a strong association between these conditions.1 A retrospective study by Chin et al examined the natural history of degenerative lumbar curves and found that 46% of patients with degenerative scoliosis had laterolisthesis greater than 5 mm at L3L4, with nonlinear progression occurring most rapidly in women older than 69 years with levoscoliosis.12 This finding underscores

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that laterolisthesis may not be merely a secondary consequence of degeneration but a primary driver of spinal deformity.

Increasing ver tebral t ranslat ion over time disrupts coronal and sagittal balance, leading to worsening asymmetric loading on the intervertebral discs and facet joint.

Marty-Poumarat et al categorized degenerative scoliosis progression into 2 types: Type A, where a pre-existing adolescent scoliosis worsens after skeletal maturity, and Type B, which develops de novo in adulthood, often in association with rotatory subluxation and laterolisthesis.13 Type B scoliosis was found to progress more rapidly, particularly around menopause.13

Development of Spinal Stenosis and Nerve Compression Laterolisthesis causes anatomical stenosis in a distinctively different way than anterolisthesis. Unlike anterolisthesis, which reduces central canal space through anterior vertebral slippage, laterolisthesis often leads to asymmetrical canal narrowing and foraminal stenosis, producing a unique pattern of neural compression.14 Nerve root stretch injury has been implicated in laterolisthesis-related radiculopathy. Kitab et al systematically reviewed the literature on stretch-related nerve injury, proposing that the dynamic nature of laterolisthesis may result in prolonged or episodic tensile forces on nerve roots, which in turn contribute to radiculopathy.15 The study highlighted that a functional spinal unit experiencing vertebral slippage can create stretch-induced nerve root injuries independent of direct compression. They

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proposed that stretch-induced injury may contribute to chronic pain syndromes, even in the absence of severe foraminal stenosis.

The pattern of neural compression depends on the nature of vertebral slippage. Liu et al found that in degenerative scoliosis with laterolisthesis, L3 and L4 nerve roots were predominantly compressed at the concave side due to foraminal stenosis, while L5 and S1 nerve roots were affected by lateral recess stenosis on the convex side.16 Gardener et al classified stenosis patterns into “open” and “closed” subluxations, with open subluxations (common at L3-L4) causing contralateral lateral recess and foraminal stenosis, while closed subluxations (L1-L2) resulted in ipsilateral stenosis.17

Clinical Presentation While the clinical presentation of laterolisthesis includes a combination of mechanical and neurological symptoms, lower back pain is the most frequent complaint.18,19 Additionally, many patients also experience lower limb radicular symptoms corresponding to the anatomical compression of nerve roots.20 This suggests that vertebral rotation and lateral translation at specific lumbar levels disproportionately contribute to radicular symptoms. As laterolisthesis often coexists with degenerative scoliosis, patients frequently experience postural and mechanical impairments. Coronal plane instability has been correlated to compensatory muscle mechanisms, antalgic gait patterns, and limited lumbar range of motion.19,21 Given the complexity of laterolisthesis’ etiology and presentation, integrating imaging studies is

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metrics aid in assessing progression and evaluating postural malalignment.

Lateral radiographs are also useful for detecting facet locking, facet joint subluxation, and sagittal malalignment, which may Radiographic Investigations develop because of compensatory postural There is a range of different imaging modaladaptations. Therefore, it is essential to recities that are essential in the investigation ognize laterolisthesis as a tri-axial deformity and management of lumbar laterolisthesis. and to assess all relevant parameters across Radiographs remain the gold standard for the necessary planes for a comprehensive assessing spinal alignment, with lateral and analysis. In the sagittal plane, key parameters anteroposterior films offering critical insight such as the sagittal vertical axis (SVA), L1-S1 into overall spine positioning. 22 When evallordosis, pelvic incidence (PI), and pelvic tilt uating lateral translation on x-ray images, (PT) offer valuable insight into changes in measurements such as segmental lateral global spinal alignment. 25 translation and coronal wedge angle are useful for assessing single-level laterolisDynamic radiograph assessments, includthesis. 23,24 The coronal sacral vertical line ing flexion-extension and lateral bending views, offer valuable insight into spinal (CSVL) ref lects global coronal alignment mechanics under different loads. Flexion-exand horizontal displacement. Together, these tension films help detect sagittal instability by revealing excessive vertebral motion in the sagittal plane, while lateral bending views assess coronal instability and curve f lexibility. 26,27 These imaging modalities are important in evaluating laterolisthesis, as lateral instabilit y has been associated with worse preoperative pain, higher ODI scores, and greater limitations in activities of daily living.27 Computed tomography (CT) is a highly valuable imaging modality for evaluating lumbar laterolisthesis. CT provides precise evaluation Figure 1. A standing anteroposterior lumbar radiograph demonstrating laterolisthesis at L4-L5, with a of bony degenerative changes measured lateral translation of 9 mm. and 3-dimensional changes seen essential for correlating patients’ clinical signs and symptoms with the underlying structural pathology in laterolisthesis.

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in laterolisthesis. 28–30 The high-resolution imaging of the bone offers comprehensive visualization of spinal anatomy, enhancing preoperative planning and surgical decision-making. Hounsfield unit (HU) values on CT have been utilized to assess bone health, serving as a prognostic factor in various aspects of spine surgery, such as pedicle screw loosening or cage subsidence in surgery. 31 These findings are crucial for preoperative planning in laterolisthesis, as they guide the approach, assess mechanical instability and compressive pathology, and determine the extent of decompression or correction necessary.

Magnetic resonance imaging (MRI) is another key modality in evaluating lumbar laterolisthesis. It provides precise visualization of central canal stenosis, lateral recess stenosis, and foraminal stenosis, aiding in identifying associated nerve impingement in laterolisthesis, which can result in combined stenotic pathology even at a single level. 32 Its ability to localize stenosis and clarify its primary source, whether due to disc herniation, ligamentum flavum hypertrophy, or facet arthropathy, is essential for accurate diagnosis and surgical planning. All of these imaging modalities not only guide clinical management but also underscore the need for standardized classification systems that capture the complexity of degenerative laterolisthesis.

Classifications of Laterolisthesis Laterolisthesis classification parallels other spondylolisthesis classifications but is more complex due to its frequent multiplanar

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involvement. Unlike anterolisthesis, which has well-established classification systems, laterolist hesis lack s a w idely accepted framework, though several methods have been proposed. For example, Ploumis et al categorized lumbar laterolisthesis severity by measuring both lateral translation displacement and intervertebral rotation using the Nash-Moe grading scale. Their classifications included Grade I (≤5 mm), Nash-Moe 0-1; Grade II (6–10 mm), Nash-Moe 0-1; and Grade III (>11mm), Nash-Moe 1-2.2 In addition to measuring lateral translation, lumbar laterolisthesis has also been classified based on the anatomic changes to the intervertebral discs, which are affected by subluxation and translation.

Laterolisthesis can be radiographically classified based on 2 key aspects: coronal plane morphology and axial rotation.

Guillaumat et al have classif ied lateral subluxations in the context of degenerative scoliosis into 3 categories—open, closed, and parallel subluxations—according to differing mechanisms and mechanical properties. 33 Open subluxations widen the disc space due to vertebral rotation; closed subluxations narrow it due to facet erosion, and parallel subluxations involve only translation, occurring without disc wedging, rotation, or facet erosion. In terms of axial rotation, several grading systems exist to quantify vertebral rotation, including Cobb, Nash-Moe, and Peridolle methods. 34 Each method serves different insights into the severity and nature of listhesis. The Cobb method divides the vertebral body into 6 sections; the region aligned with the spinous process determines

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its grading. 34 The Nash-Moe grading scale measures the percentage of convex pedicle displacement relative to vertebral width, a key factor in assessing the degenerative progression of laterolisthesis. 34,35 These classification systems are particularly useful for assessing rotational deformity and coronal plane malalignment, which are key features of degenerative lumbar laterolisthesis. Accurately classifying these abnormalities helps determine instability severity and guide surgical decision-making. While these systems help characterize degenerative patterns in laterolisthesis, their prognostic value remains unclear. Furthermore, no universally accepted classification exists for single-level lumbar degenerative laterolisthesis, highlighting the need for further research into classification systems that stratif y laterolisthesis according to clinical outcomes.

Surgical Management Decision-Making Surgical intervention for lumbar laterolisthesis is generally indicated in patients ex per iencing prog ressive neurolog ica l deficits, severe mechanical back pain, or neurogenic claudication that does not respond to conservative treatment. 36 Clinical and radiographic indications for surgery typically include worsening radiculopathy or neurogenic claudication, instability exceeding 3 mm on dynamic imaging, significant foraminal or central stenosis, and progressive coronal imbalance.37–41 While limited studies focus exclusively on lumbar laterolisthesis, research on degenerative lumbar spondy-

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lolisthesis (DLS) suggests that the presence of segmental instability and symptomatic stenosis are primary determinants in the decision to operate.42,43 The decision bet ween decompression alone and decompression with fusion depends largely on the degree of instability and facet degeneration. Patients with mild lateral translation and well-preserved facet joints may achieve satisfactory outcomes with decompression alone. Studies on DLS indicate that in carefully selected cases, decompression alone provides similar functional improvement compared to fusion over time.44 However, when lateral translation exceeds 3 mm, there is significant facet joint arthropathy, or the patient exhibits global coronal imbalance, fusion is generally recommended to prevent further instability.

The choice between minimally invasive surgery (MIS) and open surgical approaches depends on the extent of the deformity and the patient’s overall condition. MIS techniques, such as minimally invasive decompression or lateral lumbar interbody fusion (LLIF), have demonstrated advantages in reducing perioperative morbidity, blood loss, and hospital stays while providing similar long-term outcomes to open surgery in appropriately selected patients.45 However, open fusion surgery remains the preferred approach in cases of severe laterolisthesis with coronal imbalance, where extensive alignment correction is required. Decompression alone may be a viable option in cases with minimal lateral translation and stable facet joints. However, fusion should be considered in patients with significant

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instability or coronal imbalance, as studies suggest that fusion provides superior functional and pain outcomes in moderate coronal deformity (Cobb angle >20°) and that decompression alone has a lower chance of achieving clinical improvement.46,47 Further studies are needed to establish clear surgical guidelines specific to lumbar laterolisthesis and to evaluate long-term outcomes for different surgical strategies.

Surgical Technique and Approach When fusion is considered, several surgical approaches are available depending on the degree of instability, deformity progression, and associated pathology. Posterior lumbar fusion is a commonly employed fusion approach, as it provides robust stabilization and prevents progression.48 However, transforaminal lumbar interbody fusion (TLIF) or LLIF may be preferable in cases where laterolisthesis is frequently associated with disc collapse and foraminal stenosis. These techniques can restore disc height, provide indirect decompression, and address the coronal asymmetry seen in laterolisthesis, each with its unique advantages.

TLIF, a posterior approach involv ing facetectomy and partial laminectomy, provides direct and indirect decompression of the neuroforamina. 49,50 Moreover, the insertion of an asymmetric interbody cage restores disc height and provides indirect decompression.49,50 Additionally, exposure of the posterior column may allow manual reduction of severe cases of lateral subluxation. 51 Pan et al found that DLS patients with local coronal imbalance (lateral trans-

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The choice between MIS and open surgical approaches depends on the extent of deformity and the patient's condition. MIS has reduced morbidity, blood loss and hospital stay, but open fusion is preferred where extensive alignment correction is required.

lation >5 mm or disc wedging angle >5°) achieved satisfactory sagittal and coronal correction after TLIF, with postoperative functional and pain outcomes comparable to those without imbalance, despite having greater baseline malalignment and worse preoperative function and pain. 52 LLIF uses a larger and wider cage compared to TLIF, which may enable more robust restoration of disc height, ligamentotaxis, and indirect foraminal decompression, all of which are key pathomechanical contributors in laterolisthesis. 53–55 Additionally, it may provide reliable correction of coronal malalignment while minimizing disruption to the posterior elements. 54 Both approaches will likely require posterior instrumentation with pedicle screws to prevent segment motion and cage migration during the fusion process. 53,54 Ultimately, the choice of surgical approach should depend on patient-specific factors, including clinical presentation, radiographic findings, and the extent of instability or deformity.

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While high-quality evidence specific to laterolisthesis is limited, existing literature on DLS suggests that the aforementioned fusion techniques are effective in reducing slippage and improving postoperative outcomes. 50,52,56–59

Surgical Outcomes Related to Laterolisthesis Surgical outcomes in lumbar laterolisthesis are influenced by its 3-dimensional complexity, which complicates decompression, fixation, and realignment. Unlike anterolisthesis, its asymmetrical and multiplanar nature may impact surgical outcomes such as reoperation rates, pain relief, and functional improvement.

Kato et al found laterolisthesis (≥3 mm lateral translation) to be an independent predictor for reoperations (OR = 5.22) in a cohort of patients undergoing minimally invasive decompressions, suggesting the challenge of managing laterolisthesis even with a minimally invasive approach.60 Takahashi et al found that in patients undergoing asymmetrical TLIF for degenerative spondylolisthesis, concurrent local coronal imbalance was associated with significantly worse improvement in VAS back pain than those without local coronal imbalance, despite similar improvement in other clinical outcomes. 23 However, evidence highlights that while laterolisthesis presents surgical challenges, successful reduction can lead to significant functional improvement. A retrospective study investigating adult scoliosis patients found that despite a higher baseline dis-

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ability, patients with moderate to severe laterolisthesis who achieved an improvement to mild or none after surgery were twice as likely to reach clinically relevant improvement at 2 years compared to those whose laterolisthesis did not improve.61 Despite these findings supporting fusion surger y on laterolisthesis, high-qualit y literature on the surgical outcomes of laterolisthesis remains limited. Most studies focus on degenerative spondylolisthesis or laterolisthesis in the context of scoliosis, with few dedicated analyses regarding how isolated laterolisthesis impacts patient-oriented outcomes, fusion success, and complication rates. Critical aspects such as the risk of pseudarthrosis, implant failure, and adjacent segment disease in the setting of laterolisthesis remain underexplored.

Conclusion Lumbar laterolisthesis presents significant challenges in degenerative lumbar surgery, largely due to its complex dimensionality. Its multifactorial etiology, variable symptomatology, and limited high-quality evidence in literature specific to laterolisthesis further complicate diagnosis and surgical decision-making, leading to a lack of consensus about its impact on surgical outcomes. The optimal surgical approach remains debated, with questions surrounding the role of minimally invasive techniques. Future research should focus on comparing different surgical strategies and their effects on key outcomes, including symptomatic improvement, fusion rates, complication rates, and long-term surgical success. l

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45. Echt M, Bakare AA, Varela JR, et al. Comparison of minimally invasive decompression alone versus minimally invasive short-segment fusion in the setting of adult degenerative lumbar scoliosis: a propensity score–matched analysis. J Neurosurg Spine. 2023;39(3):394-403.

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50. Wong AP, Smith ZA, Stadler JA, et al. Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF). Neurosurg Clin N Am. 2014;25(2):279-304.

51. Park P, Foley KT. Minimally invasive transforaminal lumbar interbody fusion with reduction of spondylolisthesis: technique and outcomes after a minimum of 2 years’ follow-up.

Neurosurg Focus. 2008;25(2):E16.

52. Pan W, Zhao J li, Xu J, et al. Lumbar alignment and patient-reported outcomes after single-level transforaminal lumbar interbody fusion for degenerative lumbar spondylolisthesis with and without local coronal imbalance. J Neurosurg Spine. 2021;34(3):464-470.

55. Ko MJ, Park SW, Kim YB. Correction of spondylolisthesis by lateral lumbar interbody fusion compared with transforaminal lumbar interbody fusion at L4–5. J Korean Neurosurg Soc. 2019;62(4):422-431.

56. De Kunder SL, Van Kuijk SMJ, Rijkers K, et al. Transforaminal lumbar interbody fusion (TLIF) versus posterior lumbar interbody fusion (PLIF) in lumbar spondylolisthesis: a systematic review and meta-analysis. Spine J. 2017;17(11):1712-1721.

57. Pawar AY, Hughes AP, Sama AA, Girardi FP, Lebl DR, Cammisa FP. A comparative study of lateral lumbar interbody fusion and posterior lumbar interbody fusion in degenerative lumbar spondylolisthesis. Asian Spine J. 2015;9(5):668.

58. Fukuzawa T, Uehara M, Misawa H, et al. Comparison of PLIF/TLIF and LLIF for two-level degenerative lumbar spondylolisthesis. Interdisciplin Neurosurg. 2023;33:101770.

59. Fujimori T, Le H, Schairer WW, Berven SH, Qamirani E, Hu SS. Does transforaminal lumbar interbody fusion have advantages over posterolateral lumbar fusion for degenerative spondylolisthesis? Global Spine J. 2015;5(2):102-109.

60. Kato M, Namikawa T, Matsumura A, Konishi S, Nakamura H. Radiographic risk factors of reoperation following minimally invasive decompression for lumbar canal stenosis associated with degenerative scoliosis and spondylolisthesis.

Global Spine J. 2017;7(6):498-505.

61. Daniels AH, Durand WM, Lafage R, et al. Lateral thoracolumbar listhesis as an independent predictor of disability in adult scoliosis patients: multivariable assessment before and after surgical realignment.

Neurosurg. 2021;89(6):1080-1086.

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From the Department of Orthopaedic Surgery at Rush University Medical Center in Chicago, Illinois.

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Lumbar Pseudoarthrosis Evaluation and Diagnostic Work-Up Lumbar arthrodesis is a commonly employed treatment strategy in numerous spinal conditions, including degenerative pathologies, infection, tumor, trauma, and deformity. As the relative proportion of older individuals in the United States has steadily increased, there has been a similar trend in the volume of elective lumbar fusions performed, which has increased by 62.3% from 2004 to 2015.1 Despite improvements in surgical techniques, lumbar pseudoarthrosis, often defined as a failure to achieve osseous fusion by 1-year postoperatively, remains a common reason for revision surgery.2 The rates of pseudoarthrosis after lumbar spine fusions range from 5% to 35% and are dependent on several factors, including patient comorbidities, operative techniques, and diagnostic methods.3-6 While pseudoarthrosis may be asymptomatic in some patients, others can experience significant pain and disability that requiring surgical intervention.7 Given the diagnostic and technical challenges in the management of these patients, careful preoperative planning and intraoperative attention to detail are essential to optimize outcomes.

The purpose of this review is to discuss current methods for the evaluation and diagnosis of lumbar pseudoarthrosis.

In cases of persistent axial low back or radicular pain, a thorough history and physical examination should be performed. Other potential causes of persistent pain, including infection, implant failure, or adjacent seg-

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ment disease, should be ruled out Neil Mohile, MD clinically and radiographically.2 Several diagnostic modalities are available to guide clinicians with a suspicion of pseudoarthrosis.

While the utility of static radiographs is limited in diagnosing lumbar pseudoarthrosis, indirect signs include screw loosening Gregory Lopez, MD (demonstrated by lucency or haloing around the screws), implant breakage, or progression of deformity across the fused segments.8 However, without these findings, the diagnosis of pseudoarthrosis cannot be definitively made, as static radiographs have a low sensitivity/specificity compared to other imaging modalities.9 In the setting of pseudoarthrosis, there will be angular motion across the construct in the sagittal plane, which may be evident on the flexion/extension radiographs.8 While theoretically no angular motion should exist after a solidly fused construct, in actuality, there is some residual motion, which is attributed to the elastic properties of bone and limits the diagnostic utility of dynamic radiographs.10 To better understand this phenomenon, Bono et al conducted a cadaveric study and demonstrated that up to 5 degrees of motion in the sagittal plane is acceptable in a solidly fused construct, and values exceeding this number suggest a pseudoarthrosis.10 Additional methods have been described to help

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guide clinicians in making a diagnosis. The Simmons method involves the identification of two landmarks on the anterior portion of the superior and inferior vertebral body, with lines drawn through them.11 When the angle subtended by the two lines increases by greater than 2 degrees with extension, non-union is presumed.11 Nevertheless, several studies have demonstrated poor interobserver agreement in determining pseudoarthrosis with flexion/ extension radiographs, as there remains no established criteria.12,13 With a high degree of clinical suspicion, thin-section computed tomography (CT) can be a reliable option to diagnose pseudoarthrosis, with advantages over traditional radiographs.2 Although there is no universally accepted criterion, common findings include a complete absence of continuous bony trabeculation between adjacent vertebrae or peri-implant lucency that may not be readily apparent from radiographs.14 CT demonstrates a superiority in visualizing early signs of arthrodesis compared to radiographs, which often underestimate the fusion rate in the initial 6 to 9 months postoperatively.8 Furthermore, thin-section CT offers clinicians the ability to closely evaluate the facets along with the posterolateral gutter for a solid fusion. Carreon et al conducted a retrospective review of 93 prerevision thin-section CT scans over 163 fused levels among patients who had revision surgery to assess the facet joints and posterolateral gutters for fusion.15 The study noted that the probability of a solid fusion intraoperatively was higher when both posterolateral gutters were fused on CT scan (89%) compared to when both facets were fused (74%).15 When bilateral facets and posterolateral

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gutters were fused on CT scan, the probability of a solid fusion on exploration was 96%.15 The evaluation of precise anatomic detail offered by thin-section CT is also beneficial in the setting of interbody fusion assessment, where it can aid in diagnosing a “locked pseudoarthrosis,” a condition that occurs when the graft has fused to the superior and inferior endplates but remains unfused to the cage.2 Buchowski et al conducted a prospective study of 14 patients who underwent anterior cervical fusions and found that CT most closely agrees with intraoperative findings of pseudoarthrosis when compared to radiographs or MRI (p < 0.05).16 Nevertheless, CT does have some limitations, particularly in instrumented fusions, where the metallic artifact can obscure the image quality, leading to some studies demonstrating only moderate interobserver reliability.2 In MRI, solid arthrodesis is validated by high signal intensity on T1-weighted imaging and low signal intensity on T2-weighted imaging.8 On the contrary, pseudoarthrosis is associated with edema, inflammation, and hyperemic changes within the construct and is resultantly exhibited by low T1 and high T2 signal intensities.8 The primary disadvantages of an MRI are the expense and the significant metal artifact that disrupts the overall image quality.2 As a result, MRI is typically considered only when other imaging modalities prove inconclusive.8 Bone scintigraphy (bone scan) uses radioactive isotopes, commonly 99mTc-labeled diphosphonate, which enhances tissue with high metabolic activity.14 While there remains a role for this imaging modality in diagnosing

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bone infections, neoplasms, and occult fracture, its value is limited in pseudoarthrosis, with low specificity and sensitivity reported by multiple studies.2,8,17 While further validation is warranted, recent studies have demonstrated the utility of integrated single-photon emission computed tomography (SPECT/CT). In some instances, CT can overestimate the lucency in the interbody space, which may not correspond to intraoperative findings.18 Rager et al conducted a retrospective review of SPECT/CT and CT scans alone of 10 patients with recurrent back and/ or leg pain with suspicion for pseudarthrosis.18 All patients with screw loosening on CT alone demonstrated an abnormal uptake on SPECT/ CT. However, there were three discordant cases where there was lucency around the interbody cage on the CT scan but no significant uptake on SPECT/CT. All three patients improved after

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surgery without revising the cage, which may suggest that SPECT/CT can guide surgeons in determining which component of the construct may be contributing to the patient’s symptomatology.18 Further studies are warranted, as it remains unclear whether tracer uptake necessarily reflects instability due to pseudoarthrosis or physiologic remodeling after surgery. Additionally, the optimal time to obtain a SPECT/CT postoperatively is uncertain as current studies report heterogeneous data on the timeline of expected postsurgical uptake.18 Most argue that surgical exploration remains the gold standard in assessing pseudoarthrosis, as it offers the ability to directly inspect and determine the solidity of the fusion mass. However, these days, routine exploration is performed less frequently due to the advent of noninvasive imaging modalities. Exploration is often reserved for

Figure 1. Diagnosing pseudoarthrosis with thin-section computed tomography (CT): A 58-year-old woman who underwent a L4-S1 transforaminal lumbar interbody fusion with unilateral posterior fixation who presented with persistent axial and bilateral radicular leg pain. (A and B) Anteroposterior and lateral radiographs demonstrate interbody cage and posterior instrumentation from L4 to S1 with no signs of obvious screw loosening, implant failure or surrounding osteolysis. (C and D) Sagittal and coronal thin-section CT demonstrates a complete absence of bony trabeculation between L4 and L5 endplates (red arrow), confirming pseudoarthrosis at this level. On the contrary, there is evidence of an osseous fusion between the L5 and S1 endplates (white arrow).

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patients who have a high clinical suspicion and inconclusive imaging studies.8,14 Despite extensive reports on pseudoarthrosis as a complication of lumbar spine fusions, it continues to pose diagnostic and technical challenges to surgeons. The cause of a failed lumbar fusion may be multifaceted in nature as a result of significant pathology or the psychological outlook of the patient. Other causes of pain, including infection, implant failure, or adjacent segment disease, must be ruled

out prior to considering pseudoarthrosis as a diagnosis. In some cases of pseudoarthrosis, radiographs demonstrate significant instability and radiolucency of the hardware. However, radiographs are often unreliable, and other imaging modalities, such as thin-section CT, are employed (Figure 1). A thorough understanding of the imaging modalities available and their relative advantages and limitations is essential to help guide clinicians in the evaluation and diagnosis of pseudarthrosis. l

References 1. Martin BI, Mirza SK, Spina N, Spiker WR, Lawrence B, Brodke DS. Trends in lumbar fusion procedure rates and associated hospital costs for degenerative spinal diseases in the United States, 2004 to 2015. Spine (Phila Pa 1976). 2019;44(5):369-376.

2. Raizman NM, O'Brien JR, Poehling-Monaghan KL, Yu WD. Pseudarthrosis of the spine. J Am Acad Orthop Surg. 2009;17(8):494-503.

3. Berjano P, Langella F, Damilano M, et al. Fusion rate following extreme lateral lumbar interbody fusion. Eur Spine J. 2015;24 Suppl 3:369-371.

4. Levin JM, Tanenbaum JE, Steinmetz MP, Mroz TE, Overley SC. Posterolateral fusion (PLF) versus transforaminal lumbar interbody fusion (TLIF) for spondylolisthesis: a systematic review and meta-analysis.

Spine J. 2018;18(6):1088-1098.

5. Parajón A, Alimi M, Navarro-Ramirez R, et al. Minimally invasive transforaminal lumbar interbody fusion: meta-analysis of the fusion rates.

What is the optimal graft material?

Neurosurgery. 2017;81(6):958-971.

6. Deyo RA, Mirza SK, Martin BI, Kreuter W, Goodman DC, Jarvik JG. Trends, major medical complications, and charges associated with surgery for lumbar spinal stenosis in older adults.

JAMA. 2010;303(13):1259-1265.

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7. Derman PB, Singh K. Surgical strategies for the treatment of lumbar pseudarthrosis in degenerative spine surgery: a literature review and case study. HSS J. 2020;16(2):183-187.

8. Lee YP, Sclafani J, Garfin SR. Lumbar pseudarthrosis: diagnosis and treatment. In: Seminars in Spine Surgery.

Vol 23. WB Saunders; 2011:275-281.

9. Bono CM, Khandha A, Vadapalli S, Holekamp S, Goel VK, Garfin SR. Residual sagittal motion after lumbar fusion: a finite element analysis with implications on radiographic flexion-extension criteria. Spine (Phila Pa 1976). 2007;32(4):417-422.

10. Bono CM, Bawa M, White KK, et al.

Residual motion on flexion-extension radiographs after simulated lumbar arthrodesis in human cadavers. J Spinal Disord Tech. 2008;21(5):364-371.

11. Simmons JW. Posterior lumbar interbody fusion with posterior elements as chip grafts. Clin Orthop Relat Res. 1985;(193):85-89.

12. Hamill CL, Simmons ED Jr. Interobserver variability in grading lumbar fusions.

J Spinal Disord. 1997;10(5):387-390.

14. Chun DS, Baker KC, Hsu WK. Lumbar pseudarthrosis: a review of current diagnosis and treatment.

Neurosurg Focus. 2015;39(4):E10.

15. Carreon LY, Djurasovic M, Glassman SD, Sailer P. Diagnostic accuracy and reliability of fine-cut CT scans with reconstructions to determine the status of an instrumented posterolateral fusion with surgical exploration as reference standard. Spine (Phila Pa 1976). 2007;32(8):892-895.

16. Buchowski JM, Liu G, Bunmaprasert T, Rose PS, Riew KD. Anterior cervical fusion assessment: surgical exploration versus radiographic evaluation. Spine (Phila Pa 1976). 2008;33(11):1185-1191.

17. Bohnsack M, Gossé F, Rühmann O, Wenger K. The value of scintigraphy in the diagnosis of pseudarthrosis after spinal fusion surgery. J Spinal Disord. 1999;12(6):482-484.

18. Rager O, Schaller K, Payer M, Tchernin D, Ratib O, Tessitore E. SPECT/CT in differentiation of pseudarthrosis from other causes of back pain in lumbar spinal fusion: report on 10 consecutive cases.

Clin Nucl Med. 2012;37(4):339-343.

13. Taylor M, Hipp JA, Gertzbein SD, Gopinath S, Reitman CA. Observer agreement in assessing flexion-extension X-rays of the cervical spine, with and without the use of quantitative measurements of intervertebral motion. Spine J. 2007;7(6):654-658.

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From the Department of Orthopaedic Surgery at Rush University Medical Center in Chicago, Illinois.

BIOMECHANICS

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Is Segmental Plating a Superior Strategy for Multilevel ACDFs? Anterior cervical discectomy and fusion (ACDFs) is a well-established surgical treatment for common degenerative conditions of the spine, including cervical spondylotic myelopathy and cervical radiculopathy. In the setting of multilevel disease, the standard technique involves the use of a single anterior plate that spans multiple vertebral levels.1,2 Compared to single-level ACDFs, multilevel ACDFs may be associated with abnormal load-sharing distributions and increased stress applied through the long anterior plate to adjacent segments.3,4 The altered biomechanics may accelerate adjacent segment degeneration (ASD) and increase the risk of complications, including construct failure, subsidence, or pseudoarthrosis. 3,5,6 Furthermore, the prominence of long plates, along with the associated technical challenges and increased retraction time, can also lead to persistent dysphagia or even esophageal injury in rare cases.7,8 Recently, the use of segmental plating has been proposed as a means of anterior fixation and provides numerous advantages.3,9 In this opinion piece, we argue why segmental plating should be considered in the setting of multilevel ACDFs (Figure 1).

Biomechanical Stability As compared to a single long plate, the use of segmental plating provides biomechanical superiority. It is estimated that the incidence of mechanical failure after ACDFs is 0.1% to 0.9%, and appropriate fixation is critical to op-

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timizing outcomes.10 Kiapour et al Neil Mohile, MD conducted an analysis of a cadaver-validated finite element model of a cervical spine to determine the biomechanical differences between the two surgical constructs.11 Screws in the long plate experienced significantly greater pull-out forces, ranging from 35-82 Arash J. Sayari, MD N, as compared to 10-60 N in the multi-plate constructs.11 Huang et al similarly conducted a finite element model comparing single versus segmental plating.3 The maximum Von Mises stress on the interbody cage and overall fixation was lower in the segmental plating in all motion states, suggesting a decreased risk of fatigue and failure.3 Furthermore, as the extent of subsidence is directly associated with the degree of stress placed on the interbody cage, as well as differences in elastic modulus between the contact surfaces, segmental plating may play a role in decreasing subsidence, which is particularly relevant in the elderly, osteoporotic population.3 Additionally, in both 2-level and 3-level ACDF models conducted by Huang et al, the range of motion values of the adjacent segments were lower with segmental plating as compared to a single plate.3 Additionally, in the 3-level ACDF model, the maximum stress placed on the adjacent intervertebral disc was larger in the single plate compared to segmental plating during flexion, bending, and rotation movements.3

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Figure 1.

Stacked multilevel plating for a patient with three-level cervical spondylotic myelopathy.

BIOMECHANICS

The resu lts of t his biomechanical study may have implications on ASD as it has been demonstrated that the range of motion (ROM) of adjacent segments would need to increase to compensate for the absent ROM of t he fused segment.12 Additionally, excessive load distributions on the adjacent intervertebral disc may alter the nutritional acquirement, leading to degeneration.12 By limiting motion and stress on the adjacent segments, possibly by load sharing through the additional plates and screws, segmental plating may reduce the risk of ASD.3

Complications While ACDFs are an effective treatment for cervical spondylotic myelopathy and cervical radiculopathy, the overall morbidity rates vary from 13.2% to 19.3%, with dysphagia consistently being reported as the most common complication after surgery, occurring in 1.7% to 67% of cases.10,13,14 While the majority of patients typically recover within 3 months, 3% to 35% experience persistent dysphagia, which can severely impair their nutrition and overall quality of life.10,14 Among the factors associated with dysphagia, the extent of tissue dissection, operative time, and extent of retraction are consistently reported.10,14 Particularly in obese patients with a stout neck, there can be considerable technical difficulties placing a well-centered, single plate, leading to further

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dissection and retraction, causing dysphagia and potentially a disastrous esophageal injury.

In these circumstances, segmental fixation should be considered becaise in most cases, no further exposure is required and the plates and screws can be positioned in an efficient and safe manner.

Additional Considerations When compared to single-level ACDFs, multilevel ACDFs have significantly higher rates of revision, with estimates ranging from 10% to 35% at 2 years.15-17 Oftentimes, this involves revising the anterior hardware, which can pose significant challenges with a single long plate. This may require an extensive surgical exposure similar to the index surgery solely in an effort to remove the plate. In other cases, to avoid further dissection, surgeons may resort to a metal-cutting burr to cut the plate leading to metal particles, which has the potential to lead to adverse biologic reactions.18 In contrast, segmental plating affords surgeons significant advantages for revision strategies by allowing for easy removal of the shorter plate and preserving the rest of the construct if necessary.9 Disadvantages Despite the aforementioned advantages, there are disadvantages to segmental plating that should be noted. For example, the additional plates and screws increase financial costs. It is estimated that the use of two plates instead of one would increase the cost of implants between 50% to 80% for a 3-level construct and 30% to 50% for a 4-level construct.9 With increasing scrutiny of healthcare costs, further studies are warranted to justify the use of segmental

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plating by clearly demonstrating the clinical implications of the prior biomechanical studies.

While the installation of multiple smaller plates can readily be performed in an efficient manner, the additional screws applied may actually increase operative times. Furthermore, each screw placement has inherent risks, including endplate fractures, posterior vertebral wall penetration, or vertebral artery injury in rare circumstances. 3 These risks should carefully be weighed against the benefits of increased stiffness afforded by multiple screws, which may be imperative in patients with poor bone quality.

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Conclusion Segmental plating is an effective alternative to a single plate in the setting of multilevel ACDFs, with several biomechanical and technical advantages. The load sharing by the additional plates and screws may have significant clinical implications, including decreased risk of hardware failure, adjacent segment disease, and pseudoarthrosis.3,5,6 As the increased cost can be significant, additional high-quality studies are warranted to help guide surgeons in deciding which patients may benefit from the improved biomechanical stability of segmental plating. l

References Saifi C, Fein AW, Cazzulino A, et al.

Trends in resource utilization and rate of cervical disc arthroplasty and anterior cervical discectomy and fusion throughout the United States from 2006 to 2013. Spine J. 2018;18(6):1022-1029.

6. Kao TH, Wu CH, Chou YC, Chen HT, Chen WH, Tsou HK. Risk factors for subsidence in anterior cervical fusion with stand-alone polyetheretherketone (PEEK) cages: a review of 82 cases and 182 levels. Arch Orthop Trauma Surg. 2014;134( 10):1343-1351.

2.

Viswanathan VK, Manoharan SR. To plate or not to plate after a single- or two-level anterior cervical discectomy: fusion with cage-plate construct or stand-alone cage. Asian Spine J. 2017;11(1):1-3.

7. Park JB, Cho YS, Riew KD. Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg Am. 2005;87(3):558-563.

3.

Huang W, Tian Y, Wang H, et al. Comparative analysis of the biomechanics of anterior cervical discectomy and fusion with multiple segmental plates fixation versus single multilevel plate fixation: a finite element study.

BMC Musculoskelet Disord. 2022;23(1):848.

1.

4.

Stefanakis M, Luo J, Pollintine P, Dolan P, Adams MA. ISSLS Prize winner: mechanical influences in progressive intervertebral disc degeneration. Spine (Phila Pa 1976). 2014;39(17):1365-1372.

5. Zhang L, Wang J, Feng X, et al. Outcome evaluation of zero-profile device used for single-level anterior cervical discectomy and fusion with osteoporosis compared without osteoporosis: a minimum three-year follow-up study. World Neurosurg. Published online October 12, 2018. doi:10.1016/j.wneu.2018.10.024

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8. Nicholson GM, Spence I, Johnston GA. Depolarizing actions of convulsant barbiturates on isolated rat dorsal root ganglion cells. Neurosci Lett. 1988;93(2-3):330-335.

9. Razzouk J, Cheng D, Vyhmeister E, Danisa O, Cheng W. Double-plate technique for long-construct anterior cervical discectomy and fusion. Cureus. 2023;15(10):e47407.

10. Tasiou A, Giannis T, Brotis AG, et al. Anterior cervical spine surgery-associated complications in a retrospective case-control study. J Spine Surg. 2017;3(3):444-459.

11. Kiapour A, Massaad E, Joukar A, et al. Biomechanical analysis of stand-alone lumbar interbody cages versus 360° constructs: an in vitro and finite element investigation.

J Neurosurg Spine. 2021;36(6):928-936.

12. Eck JC, Humphreys SC, Lim TH, et al. Biomechanical study on the effect of cervical

spine fusion on adjacent-level intradiscal pressure and segmental motion. Spine (Phila Pa 1976). 2002;27(22):2431-2434.

13. Epstein NE. A review of complication rates for anterior cervical diskectomy and fusion (ACDF). Surg Neurol Int. 2019;10:100.

14. Fountas KN, Kapsalaki EZ, Nikolakakos LG, et al. Anterior cervical discectomy and fusion associated complications. Spine (Phila Pa 1976). 2007;32(21):2310-2317.

15. Laratta JL, Reddy HP, Bratcher KR, McGraw KE, Carreon LY, Owens RK 2nd.

Outcomes and revision rates following multilevel anterior cervical discectomy and fusion. J Spine Surg. 2018;4(3):496-500.

16. Veeravagu A, Cole T, Jiang B, Ratliff JK. Revision rates and complication incidence in single- and multilevel anterior cervical discectomy and fusion procedures: an administrative database study. Spine J. 2014;14(7):1125-1131.

17. Babici D, Johansen PM, Miller TD, Snelling B. Five-level anterior cervical discectomy and fusion. Cureus. 2021;13(11):e19961.

18. Sansone V, Pagani D, Melato M. The effects on bone cells of metal ions released from orthopaedic implants. A review. Clin Cases Miner Bone Metab. 2013;10(1):34-40.

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Harmanjeet Singh, BA

The Clinical Significance of Segmental Lumbar Lordosis in Adjacent Segment Disease

The progression of adjacent segment pathology is a leading cause of revision surgery after lumbar spinal procedures, significantly impacting patient outcomes and imposing substantial Daniel Shinn, MD costs to the healthcare system.

The development of adjacent segment disease (ASD) is often attributed to increased mechanical stress at levels adjacent to the fused segments. Adjacent segment degeneration (ASDeg) Nathan J. Lee, MD and adjacent segment disease (ASDi) have been further stratified to help define these pathologies following lumbar spinal fusion. Hilibrand and Robbins referred to ASDeg as radiographic changes seen at levels adjacent to a previous spinal procedure that do not correlate with clinical symptoms, while ASDi referred to the clinical symptoms experienced by patients that coincide with radiographic changes.1 The development of ASDeg and ASDi can severely debilitate patients and cause adverse health outcomes leading to increased revision and reoperations in the future.

Several factors have been investigated to identify the optimal approach for res-

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From the Department of Orthopedic Surgery at Midwest Orthopedics at Rush in Chicago, Illinois.

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toration during lumbar fusion surgery to minimize the development of both ASDeg and ASDi. Over the past several years, there is a growing research focus on optimizing seg menta l lumba r lordosis to mit igate the development of ASDi/ASDeg (ASD).

Therefore, the purpose of this article is to explore the recent literature on the impact of segmental lumbar lordosis in lumbar fusion surgeries.

Preoperative Evaluation Preoperat ive evaluat ion of spinopelv ic parameters and spinopelvic alignment for patients undergoing lumbar spine fusion surgery is essential to determining adequate restoration. Various studies have been conducted to assess preoperative risk factors for developing ASD, including age, gender, body mass index (BMI), number of fusion segments, and specific lumbar levels.2 Age and BMI are debated risk factors that may not serve as reliable indicators for risk stratification.

Kiss et al saw that the presence of significant degeneration in the adjacent disk level along with the presence of disk bulge/ protrusion prior to index surgery significantly increased the risk of developing ASD. 3 Similarly, Wang et al confirmed that

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preoperative Pfirrmann’s classification—a radiological method to assess the severity of intervertebral disc degeneration—greater than 3 was a significant risk factor. This highlights the importance of healthy adjacent disks to prevent adjacent segment disease development and the need for proper operative management if diseased adjacent disks are identified.

The relationship between fusion length and the development of ASD remains a topic of considerable debate. Ghiselli et al reported that patients with a multilevel fusion were significantly less likely to develop symptomatic ASD compared to those with single-level fusions.4 In contrast, Cho et al found no significant difference in ASD development between single- and multilevel fusions, complicating its use as a risk stratification method. 5 Meanwhile, Chen et al 6 utilized a finite element model to demonstrate that stress on adjacent levels increased with increasing number of fused levels, a finding corroborated by Burch et al,7 who saw higher rates of revision surgeries for ASD with longer fusion constructs.

Despite these varying perspectives, there is growing consensus on the importance of limiting surgical fusion to only the necessary levels to minimize the risk of ASD. Despite extensive research aimed at risk stratifying patients and identifying modifiable risk factors for ASD, the data remain controversial, suggesting a multifactorial nature to symptomatic degeneration.

Segmental Lordosis The lumbar spine plays an important role in

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maintaining sagittal balance and alignment.

The L4-L5-S1 spinal level contributes a large percentage of the total lumbar lordosis, with Bernhardt and Bridwell showing >60% of total lumbar lordosis is attributed to the L4-L5-S1 spinal levels. 8 This finding was corroborated by Anwar et al and Pesenti et al, but they also saw that the proximal lumbar segments correlated significantly w it h pelv ic incidence. 9,10 This suggests that loss of distal lumbar lordosis, at the L4-S1 levels, is a major contributor to loss of sagittal alignment in the spine.

Segmental lumbar lordosis is a spinopelvic parameter that can be adjusted intraoperatively and must be corrected appropriately to match preoperative levels. Kim et al reported that a low postoperative L4-L5 lordotic angle, specifically less than 20 degrees, was related with the clinical development of ASD.11 Akamaru et al corroborated this finding by showing the effects of hypolordosis in a simulated interbody fusion of L4-L5.12 Their study demonstrated that when L4-L5 was fixed in hypolordosis, the adjacent L3-L4 segment was fixed in flexion, relieving the posterior columns and allowing the facet joints to open contributing to greater degenerative changes. Umehara et al also saw that in 18 patients undergoing L4-L5 fusion, there was a 3-degree decrease in lordosis relative to preoperative level, with an associated 2-degree increase in lordosis at the proximal L2-L3 and L3-L4 segments.13 This increased lordosis at the proximal segments may predispose to sagittal malalignment and eventually could lead to postoperative complications such as lumbar disc hernia-

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Figure 1. A 70-year-old woman with grade 1 degenerative anterolisthesis at L4-5 who underwent posterior instrumented fusion from L3 to S1 in 2018. Preoperative pelvic incidence was 59 degrees, L1-S1 lumbar lordosis (LL) of 51 degrees, L4-S1 of 15 degrees. Postoperative L1-S1 LL of 55 degrees, L4-S1 of 17 degrees.

Two years later, she had severe symptomatic adjacent segment disease at L2-3 given the loss of disc height and large disc herniation necessitating revision surgery.

tion and ASD. These findings suggest that a decrease of segmental lordosis postoperatively may induce increased loading at the adjacent segment, which can contribute to lumbar disc herniation, emphasizing the importance of restoring segmental lordosis at the fused segment (Figure 1).14

Degree of Correction Historically, optimizing the relationship between pelvic incidence and lumbar lordosis was the primary radiographic alignment target. Numerous studies have shown that patients with a pelvic incidence-lumbar lordosis (PI-LL) mismatch greater than 1011 degrees exhibit higher rates of ASD.15–17 Therefore, achiev ing an opt ima l PI-LL mismatch of less than 10-11 degrees was found to be crucial in reducing the risk of adjacent segment disease. This alignment

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is particularly important for maintaining global sagittal balance in spinal deformity constructs. However, in short-segment lumbar fusions, such as single-level procedures, the PI-LL mismatch may be too broad of a target. In recent years, there has been increasing focus on segmental lumbar lordosis as a more precise parameter for alignment assessment.

In a recent retrospective study, Singh et al examined 168 patients who underwent 1- to 3-level transforaminal lumbar interbody fusions with 2-year follow up. Patients undergoing transforaminal lumbar interbody fusion (TLIF) from the L4-S1 spinal level were assessed for their lordosis correction and risk of developing adjacent segment disease.18 Inadequate correction of L4-S1 lordosis, defined as less than 35 degrees, was compared to adequate restorat ion

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(35-45 degrees) and showed significantly higher rates of ASD, instrument-related complications, and revisions in the inadequate correction cohort.18 Despite this relationship between distal lordosis and ASD development, adequate lordosis correction is a patient-specific factor that may require individualized planning.

Proximal segmental lordosis, particularly in the L1-L2-L3 segments, has shown a positive association with pelvic incidence.

A retrospective study conducted by Pesenti et al found patients with a larger pelvic incidence also exhibited a greater proximal lumbar lordosis.19 As the pelvic incidence increased, the proximal segments contributed more significantly to the overall lumbar lordosis, emphasizing the relationship between pelvic morphology and global spinal alignment. Similarly, Charles et al conducted a large-scale retrospective radiographic study of 2,599 individuals, demonstrating that global sagittal alignment increased progressively with lumbar lordosis. They also found that pelvic incidence tended to increase with age, underscoring spinal evolvement over time. 20 The importance of pelvic incidence in aligning with segmental and global sagittal alignment is reinforced through these studies and in the existing literature.

In another retrospective study, Diebo et al examined 510 patients undergoing adult spinal deformity surgery. Diebo et al observed greater rates of proximal junctional kyphosis and failure when patients were overcorrected at the thoracolumbar level and higher rates of implant failure,

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particularly rod breakage, when patients were undercorrected. 21 Matching normative PI-LL values led to improved surgical outcomes when compared to over- or undercorrection; however, determining the normative values are very patient-specific and must be individualized to the patient.

Determining appropriate reconstruction to avoid over- or undercorrection must account for patient-specific alignment targets given that the normal range of lumbar lordosis varies widely, from 18.5 to 72.3 degrees. 22

Fusion Construct There are various fusion constructs that are utilized to help treat lumbar pathologies, including disc degeneration, spondylosis, and spondylolisthesis. Surgical fusion of segments is an effective treatment option to help limit debilitating disease in patients and has become a widely utilized procedure by spinal surgeons within the past few decades. A few of the surgical options include posterior lumbar interbody fusion (PLIF), lateral lumbar interbody fusion (LLIF), transforaminal lumbar interbody fusion (TLIF) and anterior lumbar interbody fusion (ALIF).

The restoration of lordosis is crucial to helping prevent the development of ASD following spinal fusion surgery. The ability to restore lordosis can vary by fusion construct, which may help spine surgeons determine the optimal restoration technique. Watkins et al compared 3 fusion techniques (ALIF, TLIF, and LLIF) in their ability to restore lordosis and increase disk height. The study results found that the ALIF and LLIF

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Proper preoperative evaluation is a multifactorial process that must factor in age, ethnicity, BMI, comorbidities, and preoperative radiographic parameters. Achieving appropriate segmental lumbar lordosis can help mitigate ASD development while avoiding overor undercorrection.

procedure significantly improved lordosis from the preoperative state to follow-up when compared to the TLIF procedure. 23 Intergroup analysis also demonstrated the greatest amount of restoration with the ALIF technique. 23 Given the superiority of ALIF to restore lumbar lordosis, its relationship with ASD development was explored by Lee et al. 24 T hei r st udy compa red t he A LIF, LLIF, and PLIF procedure in restoring lordosis and preventing ASD, with results aligning w it h f indings from Wat k ins et al. Bot h studies demonstrated the ALIF procedure was associated with greater restoration of lumbar lordosis and a lower incidence of ASD compared to LLIF and PLIF. 24 Among fusion techniques, ALIF and LLIF have demonstrated superior lordosis restoration compared to TLIF. However, ALIF and LLIF typically require a dual approach (anterior/

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lateral and posterior) to achieve sufficient posterior stabilization, increasing surgical complex it y and morbidit y. In contrast, TLIF is performed entirely from a single posterior approach, but may result in less lordotic correction.

Conclusion Segmental lumbar lordosis plays a crucial role in the development and management of ASD. With the increasing rates of lumbar spinal fusion surgeries for various spinal pathologies, it is necessar y to elucidate proper treatment techniques to help prevent postoperative outcomes, readmissions, and revision surgeries. Proper preoperative evaluation is a multifactorial process that must factor in age, ethnicity, BMI, comorbidities, and preoperative radiographic parameters such as pelvic incidence and lumbar lordosis. Achieving appropriate segmental lumbar lordosis can help mitigate ASD development while avoiding over- or undercorrection. Additionally, determining the type of fusion construct best suited for the individual to help restore sagittal alignment is crucial in preventing future postoperative complications. This study aimed to explore the various surgical techniques and preoperative/intraoperative considerations essential for optimizing patient outcomes with significant spinal pat holog y. Fut u re resea rch w i l l need large multicentered prospective studies focused on refining patient-specific targets of correction and exploring different fusion techniques to further reduce ASD incidence. l

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References 1. Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J. 2004;4(6 Suppl):S190-S194.

11. Kim KH, Lee SH, Shim CS, et al.

Adjacent segment disease after interbody fusion and pedicle screw fixations for isolated L4-L5 spondylolisthesis. Spine. 2010;35(6):625-634.

20. Charles YP, Bauduin E, Pesenti S, et al. Variation of global sagittal alignment parameters according to gender, pelvic incidence, and age.

Clin Spine Surg. 2022;35(7):E610.

2. Liang J, Dong Y, Zhao H. Risk factors for predicting symptomatic adjacent segment degeneration requiring surgery in patients after posterior lumbar fusion. J Orthop Surg. 2014;9:97.

12. Akamaru T, Kawahara N, Tim Yoon S, et al. Adjacent segment motion after a simulated lumbar fusion in different sagittal alignments: a biomechanical analysis. Spine. 2003;28(14):1560.

21. Diebo BG, Balmaceno-Criss M, Lafage R, et al. Lumbar lordosis redistribution and segmental correction in adult spinal deformity: does it matter? Spine. 2024;49(17):1187.

3. Kiss L, Szoverfi Z, Bereczki F, et al.

Impact of patient-specific factors and spinopelvic alignment on the development of adjacent segment degeneration after short-segment lumbar fusion. Clin Spine Surg. 2023;36(7):E306-E310.

13. Umehara S, Zindrick MR, Patwardhan AG, et al. The biomechanical effect of postoperative hypolordosis in instrumented lumbar fusion on instrumented and adjacent spinal segments. Spine. 2000;25(13):1617.

22. Wang SJ, Zhang SB, Yi YY, Xu HW, Wu DS. Estimation of the ideal correction of lumbar lordosis to prevent reoperation for symptomatic adjacent segment disease after lumbar fusion in older people. BMC Musculoskelet Disord. 2020;21:429.

4. Ghiselli G, Wang JC, Bhatia NN, Hsu WK, Dawson EG. Adjacent segment degeneration in the lumbar spine. JBJS. 2004;86(7):1497.

14. Okuda S, Nagamoto Y, Takenaka S, et al. Effect of segmental lordosis on early-onset adjacent-segment disease after posterior lumbar interbody fusion. J Neurosurg Spine. 2021;35(4):454-459.

5. Cho KS, Kang SG, Yoo DS, Huh PW, Kim DS, Lee SB. Risk factors and surgical treatment for symptomatic adjacent segment degeneration after lumbar spine fusion. J Korean Neurosurg Soc. 2009;46(5):425-430.

15. Rothenfluh DA, Mueller DA, Rothenfluh E, Min K. Pelvic incidence-lumbar lordosis mismatch predisposes to adjacent segment disease after lumbar spinal fusion. Eur Spine J. 2015;24(6):1251-1258.

6. Chen CS, Cheng CK, Liu CL, Lo WH. Stress analysis of the disc adjacent to interbody fusion in lumbar spine.

Med Eng Phys. 2001;23(7):485-493.

16. Tempel ZJ, Gandhoke GS, Bolinger BD, et al. The influence of pelvic incidence and lumbar lordosis mismatch on development of symptomatic adjacent level disease following single-level transforaminal lumbar interbody fusion. Neurosurgery. 2017;80(6):880.

7. Burch MB, Wiegers NW, Patil S, Nourbakhsh A. Incidence and risk factors of reoperation in patients with adjacent segment disease: a meta-analysis. J Craniovertebr Junction Spine. 2020;11(1):9-16.

8. Bernhardt M, Bridwell KH. Segmental analysis of the sagittal plane alignment of the normal thoracic and lumbar spines and thoracolumbar junction. Spine. 1989;14(7):717-721.

9. Anwar HA, Butler JS, Yarashi T, Rajakulendran K, Molloy S. Segmental pelvic correlation (SPeC): a novel approach to understanding sagittal plane spinal alignment.

Spine J. 2015;15(12):2518-2523.

10. Pesenti S, Lafage R, Stein D, et al. The amount of proximal lumbar lordosis is related to pelvic incidence. Clin Orthop. 2018;476(8):1603-1611.

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23. Watkins RGI, Hanna R, Chang D, Watkins RGI. Sagittal alignment after lumbar interbody fusion: comparing anterior, lateral, and transforaminal approaches. Clin Spine Surg. 2014;27(5):253.

24. Lee CW, Yoon KJ, Ha SS. Which approach is advantageous to preventing development of adjacent segment disease? Comparative analysis of 3 different lumbar interbody fusion techniques (ALIF, LLIF, and PLIF) in L4-5 spondylolisthesis. World Neurosurg. 2017;105:612-622.

17. Yoon SG, Lee HC, Lee SM. Pelvic incidence–lumbar lordosis mismatch is predisposed to adjacent segment degeneration after single-level anterior lumbar interbody fusion: a retrospective case-control study.

Neurospine. 2023;20(1):301-307.

18. Singh M, Kuharski MJ, Abdel-Megid H, et al. Impact of segmental lordosis restoration during degenerative spinal fusion on two-year adjacent segment disease and revision rates. Spine.

Published online September 25, 2024. doi:10.1097/brs.0000000000005161 19. Pesenti S, Lafage R, Stein D, et al. The amount of proximal lumbar lordosis is related to pelvic incidence. Clin Orthop Relat Res. 2018;476(8):1603.

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From UCI Health in Orange County, California.

MILD Procedure What Is the Evidence?

Minimally invasive lumbar decompression (MILD) is used to treat lumbar stenosis. Lumbar stenosis results when the spinal canal is narrowed by a combination of disc protrusion into the spinal canal, buck ling of Yu-Po Lee, MD the ligamentum f lav um, and osteophyte formation from the facet joints.1,2 This can lead to nerve root compression and nerve root ischemia, which can result in radicular pain and nerve dysfunction.1,2 The radicular pain can present as pain radiating down the buttocks into the legs, which is commonly referred to as sciatica.

Nerve dysfunction can present in loss of sensation and leg weakness. The loss of sensation and leg weakness does not always present with a specific dermatomal distribution because multiple nerves are often with lumbar spinal stenosis.1,2 Lumbar stenosis can also result in neurogenic claudication.

This is a condition characterized by leg numbness, pain, or weakness that limits walking tolerance. The symptoms are often improved or relieved by sitting or leaning forward. Patients can often walk farther if they learn forward on a shopping cart. This occurs because extension decreases the cross-sectional area of the spinal canal and causes nerve root ischemia, which results in radicular leg pain and nerve dysfunction.1,2 Lumbar flexion stretches the ligamentum

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f lavum and increases the cross-sectional area of the spinal canal,1,2 which improves the symptoms and allows patients to walk farther.

In a cadaveric study, Ly et al evaluated the spinal capacity of the lumbar spine in flexion versus extension with myelograms.3 The authors found a larger capacity of dural sac of 3.5 to 6.0 mL (4.85 +/- 0.75 mL) in flexion than in extension, and the differences were highly significant (p < 0.001). In a study by Kim et al, the authors evaluated patients clinically and radiographically.4 The authors performed a comparative analysis to evaluate the association between radiologic and clinical factors. Additionally, comparative analyses were performed between t he var y ing t y pes of surgeries. A mong various radiologic factors, the baseline ligamentum flavum thickness was the only major contributing factor to the severity of claudication in the multivariate logistic regression analysis. So, there is evidence that the ligamentum f lav um is a major contributor to lumbar spinal stenosis and neurogenic claudication.

M I L D i s per for me d perc ut a ne ou s l y through a 5.1-mm port. Contrast dye is used along with f luoroscopy to identify where the thecal sac is. Using specialized cutters, lamina and ligamentum flavum are removed (Figure 1). The epidurogram contrast flow allows the physician to evaluate how much

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of a decompression was performed. Preliminary studies have been promising. Staats et al conducted a prospective, multicenter, randomized controlled trial with 26 centers participating. 5 A total of 302 patients were enrolled, with 149 randomized to MILD and 153 to standard pain management treatment with epidural steroid injections. At 6 months, the Oswestry Disability Index (ODI) improvement in the MILD group (62.2%) was significantly higher than that for in epidural steroid group (35.7%) (p < 0.001).

Longer-term follow-up of this study group has also been reported. At 2 years, there were 143 patients treated with MILD versus 131 treated with epidural steroid injections.6 At 2 years, ODI scores improved by 22.7 points, numeric rating scale improved by 3.6 points, and Zurich Claudication Questionnaire symptom severity and physical function domains improved by 1.0 and 0.8 points, respectively. There were no serious device- or procedure-related adverse events, and 1.3% experienced a device- or procedure-related adverse event.

There has been growing literature on the efficacy of the MILD procedure. Jain et al7 performed a meta-analysis of the MILD procedure and included 2 randomized controlled trials and 11 other controlled clinical studies. The authors concluded t hat t he M IL D procedu re had si m i la r complication rates as epidural injections but improved efficacy. Hence, preliminary studies on the MILD procedure have been promising and show it may be better than continuing standard conservative treatments such as epidural steroid injections

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Figure 1. Lateral fluoroscopic image of a minimally invasive lumbar decompression at L4-5.

if patients do not have long-term improvement with those treatments.

Despite these findings, there have been reports of serious postoperative complications. Tumialán et al8 described serious complications in response to a study by Mekhail et al.9 In the study by Mikhail et al,9 58 patients underwent 170 MILD procedures at 11 sites. The authors reported no major device- or procedure-related complications.

One-year data showed significant reduction of pain as measured by the visual analog scale. Improvements in physical functionality, mobility, and disability were significant as measured by the Zurich Claudication Questionnaire, 12-item Short-Form health survey, and ODI. In contrast, Tumialán et al8 reported that over a 1-year period at their center, 8 patients had refractory neurogenic claudication and 2 patients had cerebrospinal

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fluid (CSF) leaks after the MILD procedure.

One of the patients who had a CSF leak not only had a dural tear but also transected nerve roots identified during revision surgery.

In another article, Tenhoeve and Karsy10 described a case of an epidural hematoma after the MILD procedure. In their case, a 76-year-old woman with lumbar stenosis and neurogenic claudication underwent a L2-3 MILD procedure. Upon discharge following the procedure, she had worsening lumbar and left buttock and hip pain. She also had left leg radiculopathy, lower extremity weakness, and progressive bilateral numbness of her lower extremities. Computed tomography and magnetic resonance imaging showed a large dorsal epidural collection that was later identified as an epidural hematoma on surgical exploration.

Postoperatively, the patient showed improved strength and sensation in the lower extremities and reduced radicular pain. At

1- and 3-month follow-ups, she had returned to her neurological baseline. Thus, despite the growing literature that shows improved results of the MILD procedure over longterm epidural steroid injections, there is also growing literature regarding complications related to the MILD procedure.

Conclusion MILD is a minimally invasive procedure used to treat lumbar stenosis with symptomatic neurogenic claudication. There is evidence that the MILD procedure may be more efficacious than epidural steroid injections long-term. However, physicians must be alert for potential complications such as epidural hematomas and CSF leaks among other surgical complications such as nerve root injury and infections. More studies are needed to better evaluate where the MILD procedure will best fit in the treatment of patients with lumbar stenosis. l

References 1. Katz JN, Harris MB. Lumbar spinal stenosis. N Engl J Med. 2008;358:818–825.

2. Porter RW. Spinal stenosis and neurogenic claudication.

Spine. 1996;21:2016–2052.

3. Dai LY, Xu YK, Zhang WM, Zhou ZH. The effect of flexion-extension motion of the lumbar spine on the capacity of the spinal canal. An experimental study. Spine (Phila Pa 1976). 1989;14(5):523-525.

4. Kim J, Kwon WK, Cho H, et al. Ligamentum flavum hypertrophy significantly contributes to the severity of neurogenic intermittent claudication in patients with lumbar spinal canal stenosis. Medicine (Baltimore). 2022;101(36):e30171.

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5. Staats PS, Benyamin RM; MiDAS ENCORE Investigators. MiDAS ENCORE: Randomized controlled clinical trial report of 6-month results.

Pain Physician. 2016;19(2):25-38.

8. Tumialán LM, Marciano FF, Theodore N. Regarding: long-term results of percutaneous lumbar decompression mild for spinal stenosis.

Pain Pract. 2012;12:252–253.

6. Staats PS, Chafin TB, Golovac S, et al; MiDAS ENCORE Investigators. Longterm safety and efficacy of minimally invasive lumbar decompression procedure for the treatment of lumbar spinal stenosis with neurogenic claudication: 2-year results of MiDAS ENCORE. Reg Anesth Pain Med. 2018;43(7):789-794.

9. Mekhail N, Vallejo R, Coleman MH, Benyamin RM. Long-term results of percutaneous lumbar decompression mild(®) for spinal stenosis.

Pain Pract. 2012;12(3):184-193.

7. Jain S, Deer T, Sayed D, et al. Minimally invasive lumbar decompression: a review of indications, techniques, efficacy and safety.

Pain Manag. 2020;10(5):331-348.

10. Tenhoeve SA, Karsy M. Lumbar epidural hematoma as a rare complication from minimally invasive lumbar decompression. Cureus. 2023;15(12):e51083.

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From the Department of Orthopaedic Surgery at UC Davis Health in Sacramento, California.

HEALTH CARE ECONOMICS

Do Spine Surgery Trainees Bring Value to Integrated Hospital Systems?

In recent years, value-based care has emerged as a central principle in modern healthcare delivery, yet the concept of “value” remains multifaceted and context-dependent. In a hospital system, value is often defined as the relationship between the quality of care provided and the cost incurred—essentially, the health outcomes achieved per dollar spent.

For spine surgeons, this definition takes on additional complexity due to the variable cost, technical intensity, and site-specific outcomes associated with spinal procedures.

While the emphasis in value-based models has traditionally focused on patient outcomes, the contribution of trainees—residents and fellows—to the value equation remains underexplored. Programs w ith trainees may show variance in both cost and quality of care, directly and indirectly, through involvement in surgical procedures, patient management, and hospital workflows.

The present article aims to explore and quantify that value within the context of modern spine surgery practice and hospital system economics with regard to spine surgery.

How do we define value in spine surgery?

Value in healthcare is typically quantified using patient-centered outcomes relative

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Michelle Scott, MD

to expenditure. Within spine su rger y, t hese outcomes i nclude both clinical results and patient-reported outcome measures (PROMs), such as patient sat isfact ion, pain reduct ion, Hania Shahzad, MD and functional improvement.

Commonly used PROMs include the Neck Disability Index, the modified Japanese Orthopaedic Association scale for cervicothoracic disease, the Oswestry Disability Index, the Roland-Morris Safdar N. Khan, MD Disability Questionnaire for low back pain, and t he Scoliosis Research Society-22 for spinal deformity.1 These tools provide critical insight into the effectiveness of surgical interventions, t hough accurate assessment requires careful risk adjustment Hai V. Le, MD, MPH g iven t he heterogeneit y a nd complexity of spine patients.

Beyond PROMs, the concept of value in spine surgery has expanded through the framework of value-based healthcare, which emphasizes outcome measurement across the full cycle of care.2 These outcomes range include survival and functional recovery (Tier 1), time to return to daily activities

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to value-based care by enhancing clinical efficiency, standardizing protocols, and supporting data-driven outcomes tracking.

Their involvement in integrated spine teams helps ensure adherence to ev idence-based pat hways, reduces care variabilit y, and supports coordination across the surgical episode. Trainees of ten assist in col lect ing a nd maintaining PROMs, which are critical for assessing functional recovery and long-term success.

In academic and high-volume centers, they play a key role in sustaining registry participation and quality improvement initiatives, enabling benchmark ing Figure 1. This image describes the economic value of residents and trainees in spine surgery. and real-time performance monitoring. By increasing operative capacity, and complication rates (Tier 2), and the streamlining perioperative care, and resustainability of outcomes and long-term inforcing protocol compliance, trainees sequelae (Tier 3). National and international help optimize outcomes and operational spine registries, such as the American Spine efficiency, which are core drivers of value Registry, AOSpine Knowledge Forums, and in spine surgery.

SweSpine, enable benchmarking of these outcomes at scale and help standardize def init ions of va lue. 2 Addit iona lly, t he How do we measure costs in spine surgery, and where do trainees fit integration of specialized care through into the equation? multidisciplinary teams, as seen in integrated practice units, and the growth of While value in healthcare is often defined centers of excellence further align spine as outcomes relative to cost, the concept care deliver y with measurable value by of cost itself warrants closer examination, streamlining workflows, reducing variabilparticularly in the context of high-acuity, ity, and enhancing patient outcomes across resource-intensive specialties like spine anatomical and procedural complexities. surgery. The site of service also plays a role Trainees in spine surgery, such as resiin the valuation of trainees and the envidents and fellows, contribute meaningfully ronment in which they are used. Residents

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HEALTH CARE ECONOMICS

may be the “opportunity cost” in academic medical centers, while fellows may provide a different role in high-throughput outpatient surgical centers. Cost can refer to a variety of expenditures, including direct financial outlays, opportunity costs, and resource utilization; it must be understood in relation to different stakeholders: patients, hospital systems, providers, and payers. For trainees, cost considerations are rarely emphasized during clinical educat ion, yet t hey are central to how surgical care is financed, delivered, and optimized.

Unlike earlier healthcare models, where cost structures were relatively straightforward, modern reimbursement is shaped

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by third-party payers, bundled payment models, and complex billing systems. This has made accurate cost measurement increasingly challenging, especially at the individual procedure or patient level. While some hospital-related expenses—such as surgeon salaries, implants, and operating room (OR) time—are easily quantifiable, others are more difficult to allocate precisely.

To navigate this complexity, three common methodologies are employed to estimate surgical costs: the Ratio of Cost to Charges (RCC), Relative Value Units (RVUs), and Time-Driven Activity-Based Costing (TDABC) (Table 1). The RCC method ap-

Table 1. Costing Methods in the Current US Health Care System

Costing Method

Definition

Application in Spine Surgery

Real-World Example

Strengths

Limitations

Ratio of cost to charge (RCC)

Divides hospital costs by total charges; estimates cost per service using a ratio

Used for hospital-wide budgeting: limited procedures-level insight

Estimate the cost of ACDF by applying RCC to billed charges

Simple to use; effective for macro-level cost analysis

Lacks granularity; ignores patient or procedure-specific factors.

Relative Value Unit (RVU)

Measures physician work based on time, complexity, and intensity of services

Assigns RVUs to procedures such as ACDF or microdiscectomy to estimate cost and value

ACDF: 40 RVUs: Microdiscectomy: 13 RVSs; Scoliosis fusion: 70 RVUs

Reflects physician workload and complexity; standardized in reimbursement

Omits nonphysician costs; doesn’t reflect true OR resource use

Time-Driven Activity-Based Costing (TDABC)

Calculates cost by multiplying the time required for each activity by the cost per time unit

Breaks down each step (eg, surgeon time, implants) to capture actual costs per case

TDABC in posterior cervical fusion reveals implant cost drivers or OR inefficiencies

Highly detailed; identifies inefficiencies and improves resource use

Requires practice time and cost data; resource-intensive to implement

Abbreviations: ACDF = anterior cervical discectomy and fusion; OR = operating room.

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plies a standardized ratio across services to ref lect institutional cost structures but lacks specificity and does not account for clinical outcomes. 3 RV Us, on t he ot her hand, attempt to quantify the time, effort, and complexity involved in a procedure. For instance, a single-level microdiscectomy might generate significantly fewer RV Us compared to a multi-level scoliosis correction, highlighting the procedural variability inherent in spine surgery. TDABC, considered the most granular approach, calculates cost by multiplying the cost rate of a resource (eg, OR time, anesthesia, implants) by time. 3 This method is especially relevant in spine surgery, where prolonged operative times, specialized equipment, and intraoperative monitoring significantly impact resource utilization.

The OR serves as both a major cost center and a key revenue generator for hospitals, accounting for up to 40% of hospital expenditures and as much as two-thirds of overall revenue. 4 Spine surger y, with its high complexity and associated costs, plays a central role in this dynamic. Trainees— residents and fellows—are embedded within this economic equation. While requiring supervision and potentially increasing operative times initially, their participation in surgeries contributes to workforce efficiency, procedural throughput, and long-term sustainability of surgical services. Moreover, their presence can influence staffing models, case volumes, and downstream revenue through extended patient care contributions. Therefore, when assessing the cost in spine surgery, the inclusion of

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trainee-associated variables is essential to capture a more comprehensive and accurate economic picture.

How do workforce shortages and training costs affect the economic value of trainees in spine surgery?

The impending shortage of surgical specialists poses a significant challenge to the U.S. healthcare system. By 2030, it is estimated that more than 100,000 new surgeons will need to be trained to preserve adequate access to surgical care across the country. 5 Simultaneously, projections indicate a shortfall of 19,800 to 29,000 surgical specialists, underscoring an urgent need to expand training capacity.6 Despite this, the current financial infrastructure supporting surgical education remains constrained.

On average, the annual cost of training a resident, including salary, benefits, and direct expenses, is approximately $80,000. 5 These costs are primarily subsidized by federal funding allocated through the Balanced Budget Act of 1997, which imposed a cap on Medicare-supported graduate medical education positions. While this cap was temporarily expanded in 2020 by 1,000 additional slots in response to physician shortages exacerbated by the COVID-19 pandemic, the increase remains modest relative to the projected demand.

Although some institutions have turned to alternative funding mechanisms, including state support, philanthropic donations, and internal hospital resources, these sources are limited in scale. This underinvestment is striking when considered in light of the

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contribution trainees make, particularly in high-revenue departments such as surgical services. In specialties like spine surgery, where operative cases often represent a hospital’s most significant income stream, residents and fellows not only contribute to clinical productivity but also enhance system capacity and surgical volume. As the healthcare landscape braces for a widening workforce gap, reevaluating the economic value of trainees beyond their educational cost is essential for informed policy and institutional planning.

How do we evaluate the operational impact of surgical trainees in spine surgery?

W hile t he measurable economic va lue of surgical trainees is increasingly being recognized, much of their contribution lies in less tangible, yet equally critical, operational efficiencies. Admittedly, there are indirect costs associated with training residents, such as longer operative times and the additional teaching required in both the OR and clinic. However, these are often offset by substantial system-level and quality-of-life benefits for attending surgeons and the healthcare team. Many hospital systems use advanced practice providers (APPs) in both the outpatient and inpatient setting. APPs play a crucial role in hospital systems by assisting trainees in patient care, managing rising patient needs, and ensuring quality care. Unlike trainees, APPs can bill for their services, generating revenue and expanding clinic capacit y when necessary. However, some hospitals

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As the healthcare landscape braces for a widening workforce gap, reevaluating the economic value of trainees beyond their educational cost is essential for informed policy and institutional planning.

impose patient limits and restrictive policies that may hinder their full potential in the outpatient setting.

Residents enhance workflow efficiency in numerous ways: preparing and finalizing clinic notes, streamlining documentation in electronic medical records, assisting with inpatient rounding, and facilitating admissions and discharges. These contributions reduce the administrative burden on attending physicians, enabling them to spend more time with patients or their families—benefits that, while difficult to quantify financially, significantly impact surgeon well-being and reduce burnout.

In the broader context of rising healthcare costs and increasing patient demand, understanding the full value of trainees is essential. Graduate medical education is supported by an estimated $12–$14 billion annually through the Centers for Medicare and Medicaid, effectively covering resident salaries and training costs.4 With this major cost already externally subsidized, the remaining question is: what do residents and fellows bring to the system in return?

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Recent studies have begun to quantify their impact, showing that surgical trainees can improve hospital performance and contribute positively to financial outcomes without compromising safety. In high-demand fields like spine surgery, where OR setup and case complexity often limit daily volume, residents and fellows help optimize block time and increase throughput. For instance, while the attending completes closure and final imaging in one room, a resident may initiate the next case, enhancing surgical flow and maximizing resource use. Additionally, their role in extending emergency coverage and crossroom support adds further operational value.

From the perspective of a surgical trainee, the ability to support efficient, high-quality care while alleviating the workload for attendings affirms their role not only as learners but also as integral members of the hospital ecosystem. Their contributions, both direct and indirect, should be recognized as essential to sustaining and advancing

surgical care delivery in a system facing increasing demand and workforce shortages.

Conclusion Understa nd i ng t he econom ic va lue of trainees in spine surgery requires a comprehensive framework that accounts for their impact on operative efficiency, complication rates, educational costs, and long-term workforce sustainability. To fully tap the potential of trainees in spine surgery, future models should integrate them intentionally into value-based care initiatives through structured roles in clinical efficiency, outcomes tracking, and multidisciplinary care pathways. Institutions must also explore mechanisms to equitably recognize and compensate their contributions, ensuring that the value trainees bring to the system is reciprocated with meaningful educational, professional, and financial support.

Aligning institutional goals with trainee development will be key to sustaining a high-value surgical workforce. l

References 1. Beighley A, Zhang A, Huang B, et al. Patient-reported outcome measures in spine surgery: a systematic review. J Craniovertebr Junct Spine. 2022;13(4):378.

2. Karhade AV, Bono CM, Makhni MC, et al. Value-based health care in spine: where do we go from here?

Spine J. 2021;21(9):1409-1413.

3. Hennrikus WP, Virk SS. Inside the value revolution at Children’s Hospital Boston: time-driven activity-based costing in orthopaedic surgery.

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Harvard Orthop J. 2012;14:50-57.

4. Scarola S, Morrison L, Gandsas A, Cahan M, Turcotte J, Weltz A. Evaluating the impact of surgical residents on hospital quality and operational metrics. J Surg Ed. 2025;82(2):103374.

5. Williams TEJ, Satiani B, Thomas A, Ellison EC. The impending shortage and the estimated cost of training the future surgical workforce.

Ann Surg. 2009;250(4):590.

6. Kirch DG, Petelle K. Addressing the physician shortage: the per-

il of ignoring demography. JAMA. 2017;317(19):1947-1948.

7. Katz AD, Song J, Bowles D, et al. What is a better value for your time? Anterior cervical discectomy and fusion versus cervical disc arthroplasty. J Craniovertebr Junct Spine. 2022;13(3):331.

8. Lorio D, Twetten M, Golish SR, Lorio MP. Determination of Work Relative Value Units for management of lumbar spinal stenosis by open decompression and interlaminar stabilization.

Int J Spine Surg. 2021;15(1):1-11.

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From DISC Sports and Spine Centers in Newport Beach, California.

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A Primer on Direct Care and Direct-to-Employer Contracting for Spine Surgeons Brandon P. Hirsch, MD

In the 15 years following enactment of the Affordable Care Act, the share of patient responsibility for healthcare costs in the United States has grown dramatically. According to the Kaiser Family Foundation, the average annual premium for employer-sponsored family health coverage in the United States has increased by approximately 47%, rising from $16,029 in 2013 to $23,968 in 2023. This growth has outpaced the general inflation rate of 30% over the same period.1 In conjunction with rising premiums, enrollment in high-deductible health plans has also increased dramatically over the past decade, shifting even further financial responsibility to patients (Figure 1).1 As deductibles rise and patients bear a greater share of cost, many are seeking predictability and transparency in how they access care. For spine surgeons, this shift opens the door to models that bypass traditional insurance altogether—namely, direct care and direct-to-employer (DTE) contracting.

These alternative payment strategies offer the potential to streamline operations, reduce administrative burden, and restore physician autonomy in delivering spine care.

Understanding Direct Care: A PatientDriven Shift Direct care refers to the delivery of healthcare services outside the conventional insurance

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framework. Patients pay their physicians directly—typically via bundled pricing—for defined episodes of care. In spine surgery, this would include all-inclusive pricing for procedures, encompassing the preoperative visit, imaging, surgery, anesthesia, facility fees, and postoperative follow-up.

The model was originally established by direct primary care (DPC), in which patients pay a monthly membership fee for comprehensive access to primary services. Like DPC, direct care in surgery eliminates third-party utilization management, surprise billing, and opaque cost structures. Instead, it emphasizes transparency, timely access, and clear delineation of services included in the episode of care.

This philosophy has gained momentum as more patients find themselves in high-deductible health plans (HDHPs), often exceeding $5,000 annually for individual coverage.1 For patients with these plans, using insurance can actually be more costly than paying a cash discounted rate.

Health Sharing Ministries and Other Parallel Models Some direct care patients navigate their healthcare using nontraditional financing arrangements. Health sharing ministries (HSMs), for example, are faith-based organizations in

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Figure 1.

Growth of high-deductible health plans in the United States between 2013 and 2023.

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which members contribute monthly shares to fund the medical needs of others. While not considered insurance under federal law, these ministries often reimburse major surgical expenses when members submit pre-negotiated, transparent invoices from physicians.2 A recent report from the State of Colorado Division of Insurance found that more than 1.5 million Americans now participate in health care sharing programs.3 These patients are highly motivated to find value-based care options and often seek out surgical centers and physicians who can provide comprehensive, upfront pricing. Other similar noninsurance arrangements have emerged as well, including medical cost-sharing cooperatives and healthcare savings account–based models.

The Mechanics of Direct-to-Employer Contracting While individual patients are driving interest in direct care, employers are also evaluating alternatives to the traditional insurance model.

Employer-based health plans typically fall into three categories: fully insured, self-funded, and level-funded. In a fully insured plan, the employer pays fixed premiums to an insurance

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carrier, which assumes all financial risk and handles claims. Self-funded plans, by contrast, involve the employer directly funding employee medical claims, often with the help of a third-party administrator (TPA). Level-funded plans blend features of both, with employers paying a predictable monthly amount that includes administrative costs, claims funding, and stop-loss coverage to limit risk. If claims are lower than expected, the employer may receive a rebate.

One of the primary drivers behind the rise in direct-to-employer contracting is growing dissatisfaction with traditional insurance carriers and third-party administrators (TPAs).

In many self-funded employer health plans, TPAs manage claims and networks while the employer bears the financial risk. These administrators often negotiate discounts with facilities and surgeons but retain a portion of those savings—a practice known as “the spread.” For example, a facility may agree to perform a procedure for $20,000, but the TPA may bill the employer $25,000, keeping the $5,000 difference. This spread is rarely visible to employers due to opaque pricing structures and proprietary contract language. Employers assume they are paying a discounted rate, when in fact, intermediaries may be adding margin without contributing to clinical value.

Over time, this lack of transparency has led large, self-insured employers to reevaluate their relationships with TPAs. Direct-to-employer (DTE) contracting enables physicians to negotiate directly with companies, offering surgical care packages that often include the procedure in addition to navigation services, travel coordination,

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and postoperative rehabilitation. As a result, more employers are seeking direct relationships with high-value practices through DTE arrangements. By bypassing TPAs, employers can negotiate fixed prices, demand measurable outcomes, and better align incentives while eliminating the costs associated with the spread. For spine surgeons, this creates an opportunity to contract directly with benefit managers or human resource teams to deliver predictable, evidence-based care at a known cost. DTE contracts have become increasingly popular among large employers with self-funded plans. Programs like Walmart’s Centers of Excellence, which contract directly with high-performing spine centers, have demonstrated measurable reductions in cost and improved outcomes.4 Surgeons who can demonstrate low complication rates, strong patient satisfaction, and cost efficiency should find themselves well-positioned in this space.

Operational Considerations for Spine Surgeons Implementing a direct care or DTE model requires familiarity with healthcare pricing.

Surgeons must be able to quote accurate, bundled rates and often collaborate with facilities to streamline contracts. Administrative support is necessary to handle direct billing,

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communicate with patients or employers, and ensure that care episodes include the full scope of services. Many successful practices develop dedicated landing pages or concierge teams to assist direct pay patients from consultation through recovery.

In the DTE context, quality metrics become essential. Employers expect transparency around outcomes, complication rates, and readmissions. Participation in national registries (eg, National Surgical Quality Improvement Program or Quality Outcomes Database) or the use of internal benchmarking tools can strengthen negotiating positions. Establishing pathways for travel, preoperative clearance, and remote follow-up also helps make DTE contracts scalable.

Conclusion Direct care and direct-to-employer contracting offer more than just alternative payment models—they represent a philosophical shift in healthcare and spine surgery delivery. They re-center the relationship between surgeon and patient, strip away unnecessary intermediaries, and focus on value, transparency, and access. As dissatisfaction with traditional coverage grows, spine surgeons who can adapt to these models may not only thrive economically, but also lead the way in redefining the patient experience. l

References 1. Kaiser Family Foundation. 2023 Employer Health Benefits Survey. Published October 18, 2023. Accessed April 14, 2025. https://www.kff. org/report-section/ehbs-2023-section-1-cost-of-health-insurance/

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2. Barlow J. Health care sharing ministries.

The Actuary Magazine. March 2018. https://www.theactuarymagazine. org/health-care-sharing-ministries/ 3. Colorado Division of Insurance. Health Care Sharing Plans and Arrangements in Colorado, 2023: Report Pursuant to House Bill 22-1269. Colorado Depart-

ment of Regulatory Agencies; October 2024. https://doi.colorado.gov/ health-care-sharing-associations 4. HBR Editors. two surgeries, two outcomes. Harvard Business Review. March 18, 2019. https://hbr.org/2019/03/ two-surgeries-two-outcomes

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