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SPINE Volume 29, Number 22, pp E515–E519 ©2004, Lippincott Williams & Wilkins, Inc.

Changes in the Cross-Sectional Area of Multifidus and Psoas in Patients With Unilateral Back Pain The Relationship to Pain and Disability Karen L. Barker, PhD,MCSP,* Delva R. Shamley, PhD,† and David Jackson, PhD, MCSP†

Study Design. Prospective, cross-sectional observational study. Objectives. The aim of this study was to determine if there was an association between wasting of psoas and multifidus as observed on MRI scans and the presenting symptoms, reported pathology, pain, or disability of a cohort of patients presenting with unilateral low back pain. Summary of Background Data. Current physiotherapy practice is often based on localized spine stabilizing muscle exercises; most attention has been focused on transversus abdominus and multifidus with relatively little on psoas. Method. Fifty consecutive patients presenting to a back pain triage clinic with unilateral low back pain lasting more than 12 weeks were recruited. The cross-sectional surface area (CSA) of the muscles was measured. Duration of symptoms, rating of pain, self-reported function, and the presence of neural compression were recorded. Results. Data analysis compared the CSA between the symptomatic and asymptomatic sides. There was a statistically significant difference in CSA between the sides (P ⬍ 0.001). There was a positive correlation between the percentage decrease in CSA of psoas on the affected side and with the rating of pain (rho ⫽ 0.608, P ⬍ 0.01), reported nerve root compression (rho ⫽ 0.812, P ⬍ 0.01), and the duration of symptoms (rho ⫽ 0.886, P ⬍ 0.01). There was an association between decrease in the CSA of multifidus and duration of symptoms. Conclusions. Atrophy of multifidus has been used as one of the rationales for spine stabilization exercises. The evidence of coexisting atrophy of psoas and multifidus suggests that a future area for study should be selective exercise training of psoas, which is less commonly used in clinical practice. Key words: psoas, multifidus, cross-sectional area, rehabilitation, back pain. Spine 2004;29:E515–E519

Low back pain (LBP) is a common problem with inadequate correlation between investigative findings, clinical symptoms, and treatment strategies.1 In recent years, there has been a trend by physiotherapists to consider the

local muscle system in the treatment of spinal pain. Attention is focused on specific muscle training aimed at enhancing the activity of the postural muscles that stabilize the spine.2–7 Multifidus and psoas both act to provide stability to the spine and are sensitive to pathologic changes. Multifidus provides stability to the spine biomechanically,8 and by virtue of its segmental attachment and innervation.9 Imaging techniques have shown wasting of multifidus in patients with LBP,10,11 and specific multifidus strengthening exercises have been reported to decrease pain and the recurrence of LBP.12–14 Multifidus exercises are now established practice in the rehabilitation of patients with LBP.15 More recently, attention has been focused on the role of psoas major in stabilizing the spine. Biomechanical models suggest that it may achieve this function through its large potential to generate compressive forces, which increases spinal stiffness.16 Studies reporting the effect of spinal pathology on psoas size are contradictory. Danneels et al17 reported no change in psoas cross sectional area (CSA) in patients with LBP compared with controls but a significant decrease in multifidus CSA. Conversely, Cooper et al18 and Dangaria and Naesh19 reported a significant decrease in ipsilateral psoas CSA in the presence of LBP and disc herniation. Despite a number of studies that have documented the size and appearance of the trunk muscles and the effect of retraining programs, most studies have concentrated on specific muscles in isolation. To date, no study has investigated the CSA of both multifidus and psoas in the presence of unilateral LBP. The aim of this study was to determine if there was an association between wasting of these muscles as observed on MRI scans, the presenting symptoms, reported pathology, pain, and disability of a cohort of patients presenting with unilateral LBP. Materials and Methods Subjects. Fifty consecutive patients who presented to a back

From the *Physiotherapy Research Unit, Nuffield Orthopaedic Centre NHS Trust; and †School of Physiotherapy, Oxford Brookes University, Oxford, UK. Acknowledgment date: September 23, 2003. First revision date: January 8, 2004. Acceptance date: February 5, 2004. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to Karen L. Barker, PhD, MCSP, Physiotherapy Research Unit, Nuffield Orthopaedic Centre NHS Trust, Windmill Road, Oxford, OX3 7LD UK; E-mail:

pain triage clinic with a clinical presentation of unilateral LBP were recruited to the study. Patients were between 18 and 65 years of age and had a history of unilateral lower back pain lasting at least 12 weeks. Unilateral back pain was diagnosed clinically, based on a patient report of a preponderance of symptoms on one side of the lower back, or referral to one lower limb. Patients were excluded from the study if they had had previous back surgery, had a history suggestive of spondylolisthesis, or had any systemic disorders. All patients gave informed consent for their clinical details and scans to be used in the study, for which ethical committee approval had been obtained. Patients were referred for a magE515

E516 Spine • Volume 29 • Number 22 • 2004 scan was assessed using the criteria of Boos et al,22 where the minor category included contact with the nerve root, thecal sac, or displacement of the nerve root and the major category was defined as nerve compression. The radiologic assessments were carried out blind, without knowing the symptomatic side.

Measurement Reliability. All measurements were taken by the same person. Intratester reliability was assessed by repeated measuring of 10 of the 48 scans. An intraclass correlation coefficient was calculated to assess if there were any significant differences between the original and repeat measurements.

Figure 1. Measurement of cross-sectional area of muscle. Dotted line indicates polygon outlining muscle boundary. netic resonance imaging (MRI) scan and these were subsequently studied and measured. In 2 of the cases, it was not possible to obtain an MRI scan because of claustrophobia; further analysis was based on the 48 patients who completed MRI scanning.

Measures and Procedures. All MRI examinations were performed using a 1.5-T superconducting magnet (Magnetom Symphony, Siemens AG, Erlangen, Germany). The patients were placed supine with a pillow positioned underneath the knees, ensuring that the patient was lying symmetrically with weight evenly distributed across both sides. Sagittal and axial sections were obtained, sampling with an interslice gap of 4 mm for sagittal slices and 5 mm for axial slices. From each MRI scan, the level indicated by the clinical presentation of the patient was measured, together with one vertebral level above and one below. The MRI scans showed 4 images per spinal level. The most central picture was chosen, provided that it had adequate picture quality. The scans were photographed using a digital camera and downloaded into an auto-CAD package. Each image was enlarged for clearer viewing and scaled according to the scale on the MRI photograph. The left and right psoas and multifidus muscles were measured on each scan using the CSA by constructing polygon points around the outer margins of the muscles. The number of points selected for each scan varied according to the size and shape of the muscle but was typically between 20 and 30 points and created a polygon that replicated the shape of the underlying muscle. The auto-CAD package was used to calculate the area contained within the polygon, i.e., the CSA of the muscle (Figure 1). Demographic data of the patients’ age, duration of symptoms, and gender were collected. Patients were also asked to complete a visual analogue rating scale of the level of their pain20 and a self-reported measure of function, the Oswestry Disability Index.21 The presence of neural compression on the Table 1. Patient Characteristics

Age (yr) Duration of symptoms (wk) Pain (Visual Analogue Score/10) Oswserty Disability Index (%)



Standard Deviation

44.3 15.6 7.4 38.4

19–65 12–26 4.4–10 12–76

11.8 5.8 1.47 14.7

Data Analysis. Data were analyzed comparing the CSA of the muscles on the symptomatic and asymptomatic sides using nonparametric methods. A Wilcoxon rank sum test was used to test the difference between the paired measurements of CSA in individual patients. Associations between clinical variables and the decrease in CSA on the symptomatic side were tested using Spearman’s test for correlation. A significance level of P ⬍ 0.05 was set. Results The assessment of measurement repeatability showed good agreement between the two measurements for both psoas and multifidus (ICC 0.92, 0.89), indicating that the measures were reliable. Twenty-six of the patients were male and 22 were female. Further demographic and clinical details of the subjects are shown in Table 1. In 28 patients, the presenting symptoms were right sided and in 20 left-sided. In 3 (4%) of the patients, the clinically indicated level was L2/3, in 4 (6%) L3/4, in 33 (48%) L4/5, and in 28 (42%) L5/S1. The measurements of the CSA of the multifidus and psoas muscles are presented in Tables 2 and 3. It can be seen that the reduction in CSA was greatest at the level that correlates to the clinically indicated spinal segment level. There were also smaller, but statistically significant, decreases in the CSA of the muscles at the level above and below the clinically indicated level. Table 4 demonstrates that in the majority of cases the maximum CSA of the trunk muscles was smallest on the symptomatic side for back pain. The median decrease in the CSA of the symptomatic side for multifidus was 21.7% (range, 2.7⫺61.2%; 95% CI, 17.9⫺25.4%) at the symptomatic level (P ⬍ 0.001); 15.8% (range, 0.3–55%; 95% CI, 13.0 –18.6%) at the level above the symptomatic level (P ⬍ 0.001), and 16.8% (range, 0 – 43%; 95% CI, 14.1–19.4%) at the level below the symptomatic level (P ⬍ 0.001). The percentage decrease in the CSA of multifidus at the symptomatic level was positively correlated with the duration of symptoms (Spearman’s rho 0.872, P ⬍ 0.01). The median reduction for psoas CSA was 12.3% (range, 0.2–35.8%; 95% CI, 9.7–14.7) at the symptomatic level (P ⬍ 0.001); 2.5% (range, ⫺0.5–25.17%; 95% CI, 1.08 –3.82) at the level above the symptomatic level (P ⬍ 0.001), and 8.7% (range, 0.4 –25.3%; 95% CI, 6.5–10.5) at the level below the symptomatic level (P ⬍ 0.001) (Figure 2).

Multifidus and Psoas in Unilateral Back Pain • Barker et al E517

Table 2. Cross-sectional Area (CSA) of the Multifidus Muscle in Patients With Unilateral Low Back Pain

Patients with unilateral symptoms on right (n ⫽ 28) Patients with unilateral symptoms on left (n ⫽ 20)

One Above Problem Level CSA; Right Side Median; Range SD (mm2)

One Above Problem Level CSA; Left Side Median; Range SD (mm2)

47.3 9.02–85.2 21.52 53.4 11.3–92.7 22.76

54.9 11.3–92.7 22.53 46.6* 9.0–85.2 21.90

% Difference

Symptomatic Level CSA; Right Side Median; Range SD (mm2)

Symptomatic Level CSA; Left Side Median; Range SD (mm2)

15.2* 0.3–54 11.5 15.9* 3–43 11.3

49.7 19.6–110.7 21.91 61.7 36.8–121.9 22.26

59.5 36.8–121.9 21.13 49.7* 19.6–110.7 23.08

% Difference

One Below Problem Level CSA; Right Side Median; Range SD (mm2)

One Below Problem Level CSA; Left Side Median; Range SD (mm2)

% Difference

21.1* 3–61 15 21.6* 6–56 17

54.2 24.4–96.8 19.81 64.6 28.7–106.7 19.88

64.4 29.7–107.6 20.74 54.2 26.9–94.7 18.05

18.2* 5–43 10.5 12.8* 0–36 10.15

*Significant difference between the two sides measured at P ⬍ 0.001.

There was a positive correlation between the percentage decrease in the CSA of psoas on the affected side and with the visual analogue rating of pain (rho ⫽ 0.608, P ⬍ 0.01). Similarly, there was a positive correlation between the percentage decrease in CSA and the report of nerve root compression on the radiologists’ report of the MRI scan (rho ⫽ 0.812, P ⬍ 0.01). There was also a positive association with the duration of symptoms and the percentage decrease in CSA (rho ⫽ 0.886, P ⬍ 0.01). There was no association between the Oswestry disability function score and the percentage decrease in CSA, nor with the patients’ age or gender. Discussion The results of this study confirm that of others, that there is selective ipsilateral atrophy of the lumbar stabilizing muscles in the presence of unilateral LBP and that these changes are specific to the side that is symptomatic, a finding previously reported by Stokes et al11 and Kader et al.1However, in contrast to Kader et al,1multifidus atrophy was localized to the segment with nerve root compression or irritation, whereas Kader et al1found bilateral and multilevel muscle degeneration, even in patients with single nerve root irritation. They postulated that the atrophy of multifidus was due to lumbar dorsal ramus syndrome, with referred leg pain induced by irritation to structures innervated by the dorsal ramus nerve, triggering a self-sustained vicious cycle that promotes muscle atrophy. Psoas measurement showed a marked ipsilateral decrease in CSA at the clinically symptomatic level between L1 and L5, in agreement with the report of Dangaria and

Naesh.19 Conversely, Danneels et al17 found that there was only a statistically significant difference between the CSA of scans of healthy people and patients with LBP at the lower endplate of L4, not related to localized segment in patients with chronic LBP. Hides et al7,12 demonstrated unilateral muscle wastage in acute LBP, isolated to one level. The fact that the muscle changes were so specific suggests that the mechanism was not generalized disuse atrophy or inhibition, but a more specific process. Inhibition along a long loop reflex, targeting the vertebral level of symptoms to protect damaged tissues has been postulated as the most likely cause of muscle wasting in the acute stage after unilateral injury.18,23 Other reports suggest different explanations for the observation of unilateral wasting. Parkkola et al24 suggest that the disuse and inflammation that arise with LBP cause disuse atrophy of the back musculature. Similarly, Danneels et al17 suggest that pain is responsible for inhibition of the stabilizing muscles by a combination of reflex inhibition and changes in coordination of the trunk muscles. Dangaria and Naesh19 suggest that unilateral reduction in psoas may be due to disuse atrophy of the muscle or to compensatory hypertrophy of the psoas muscle on the opposite side. However, Mattila et al25 regard muscle atrophy to be a consequence of an inactive lifestyle, rather than due to specific spinal pathology. Danneels et al17 also concede that the atrophy may not be secondary to pain, but that there could be an etiologic relationship. Previous studies have established that the deep intrinsic muscles of the spine are recruited to control transla-

Table 3. Cross-sectional Area (CSA) of the Iliopsoas Muscle in Patients With Unilateral Low Back Pain

Patients with unilateral symptoms on right (n ⫽ 28) Patients with unilateral symptoms on left (n ⫽ 20)

One Above Problem Level CSA; Right Side Median; Range SD (mm2)

One Above Problem Level CSA; Left Side Median; Range SD (mm2)

151 67.8–287 55 146.4 77–294 58.2

147.3 72.3–294 60.5 145.1 75.6–287 57.2

% Difference

Symptomatic Level CSA; Right Side Median; Range SD (mm2)

Symptomatic Level CSA; Left Side Median; Range SD (mm2)

3.2* 0.5–25 5.9 1.3* 0.2–4.7 1.6

173 74.2–285 56.1 197.7 139–321 51.6

194.9 79.5–321 62.2 179.7 113–254 43.3

*Significant difference between the two sides measured at P ⬍ 0.05. †Significant difference between the two sides measured at P ⬍ 0.001.

% Difference 12.15† 0.2–36 8.8 12.4† 2.9–35

One Below Problem Level CSA; Right Side Median; Range SD (mm2)

One Below Problem Level CSA; Left Side Median; Range SD (mm2)

% Difference

171.4 74.2–285 57 175.6 80.3–313 60.4

187.2 79.5–300 62 159.1 79–284 52.3

9.3† 0.3–24 6.4 7.7† 0.3–24 6.7

E518 Spine • Volume 29 • Number 22 • 2004

Table 4. Association Between Cross-sectional Area (CSA) and Clinically Symptomatic Level (n ⴝ 48) At Clinically One Level Above One Level Below Symptomatic Clinically Clinically Level Symptomatic Level Symptomatic Level CSA smaller on affected side Multifidus Psoas CSA larger on affected side Multifidus Psoas CSA equal between sides Multifidus Psoas

44 38

43 39

42 42

0 2

2 4

1 2

4 8

3 5

5 4

tion and rotation at the intervertebral level, enabling spinal stiffness. Thus, changes in the recruitment of these muscles will compromise intervertebral stability.13 This study and those of Stokes et al,11 Danneels et al,17 and Hides et al23 reporting multifidus wasting have been used to argue for increased use of segmental stabilizing training, in order to try and prevent the high recurrence of episodes of back pain. If local stability dysfunction develops after the onset of pain and pathology, it is argued that as pain and dysfunction are interrelated, pain may resolve but dysfunction persist, predisposing to recurrence of symptoms.14 To date, most attention has focused on selective training of the stabilizing muscle system, particularly multifidus and transversus abdominus.4,5,13,15 It is known that exercises that recruit psoas may coactivate with, or facilitate, transversus abdominus or lumbar multifidus. Clinically, a regimen of iliopsoas muscle stretching is used in the treatment of lumbar spine disorders, with the assumption that this will improve lumbar mobility26; however, relatively little effort

has concentrated on strengthening of psoas as a treatment strategy. The impact of selective muscle training of the psoas muscle on symptoms of LBP has yet to be established. The clinical significance of changes in muscle size has yet to be proven. Indeed, it remains to be determined whether muscle control problems cause LBP or if LBP is a trigger for muscle control problems.14 Furthermore, there remains debate about whether specific localized stabilizing exercises are more effective than more general exercise fitness programs for back rehabilitation. Undoubtedly, there is much current work showing that local stabilization in the spine is important; this needs to be added to the existing strong evidence for more general exercises27–29 to enable the optimum package of back rehabilitation exercises to be prescribed. This study has a number of limitations. The study sample size is small, although comparable with other similar studies.18,19 The MRI scans were all taken in a supine position. Images obtained in this position may not reflect the actual tissue relationships that provoke symptoms and may not accurately represent the relationships of the muscles that exist during functional activities. While the repeated measures testing showed good repeatability for the method of measuring the CSA of the muscles, there was a potential for error in constructing the polygons around the margins of each muscle. Measures were taken to minimize this error by having the same person take all of the CSA measurements. Muscle degeneration may be detected by decreased muscle CSA and by increased amounts of fatty deposit within the muscle. The measurement technique we used only gave a gross measurement of muscle CSA and did not allow any computation of replacement of muscle by fatty or connective tissues. Those studies that have calculated both CSA and fatty tissue deposit have reported the presence of both signs of muscle degeneration concomitantly.1,17,18 Key Points

Figure 2. Difference in cross-sectional area between affected and contralateral side of pain.

● Current physiotherapy practice is focused on using specific muscle training aimed at enhancing the activity of the postural muscles that stabilize the spine. There is contradictory evidence from existing studies about the association between the crosssectional area of the trunk stabilizing muscles and the presence of unilateral low back pain. Most studies have concentrated on specific muscles in isolation and not related changes to presenting symptoms, pain, or disability. ● Fifty patients with unilateral back pain underwent MRI scanning and completed self-report measures of pain and disability. The relationships between changes in the cross-sectional area of the psoas and multifidus muscles and the presenting signs and symptoms were investigated.

Multifidus and Psoas in Unilateral Back Pain • Barker et al E519

● The study found selective ipsilateral atrophy of the lumbar stabilizing muscles in the presence of unilateral low back pain, which were specific to the symptomatic side. ● Atrophy of the multifidus has been used as a rationale for spine stabilizing exercises; it is suggested that future rehabilitation research investigates the use of selective strength training of psoas.

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Mudanças na área transversal do Psoas e Multífidos em indivíduos com dor lombar unilateral  

A prática atual em fisioterapia é focada na utilização de treinos musculares específicos direcionada a melhorar a atividade dos músculos pos...