8 minute read
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- timizing outcomes.10 Kiapour et al 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 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
The results of this 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 the 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
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 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.
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.
References
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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.
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.
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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.
Contributors:
Neil Mohile, MD
Arash J. Sayari, MD
From the Department of Orthopaedic Surgery at Rush University Medical Center in Chicago, Illinois.
