Asymmetric atrophy of multifidus muscle in patients with unilateral lumbosacral radiculopathy.

STUDY

DESIGN

Prospective case-control study of multifidus muscle atrophy in 39 patients with unilateral lumbosacral radiculopathy and lumbosacral disc herniation and 20 controls.

OBJECTIVE

To evaluate quantitatively the asymmetry of multifidus muscles in unilateral lumbosacral radiculopathy with disc herniation (herniated intervertebral disc; HIVD) by using magnetic resonance imaging (MRI).

SUMMARY OF BACKGROUND DATA: Histologic and morphologic changes of multifidus muscles have been reported in lumbosacral disc herniation, but there are few imaging studies on the changes of multifidus muscles in unilateral radiculopathy.

METHODS

Bilateral multifidus muscles in L3-L4, L4-L5, and L5-S1 levels were detected in fast spin-echo T1 axial MRI images. The total cross-sectional area (CSA) of multifidus muscles (TMA) and the density of pure muscle CSA (PMA) were measured by a computerized analysis program, and the ratios of PMA to TMA (PMA/TMA) and the PMA ratios of involved to uninvolved sides (IMA/UMA) were calculated. The patients were divided into 2 groups according to the electrodiagnosis results: a radiculopathy (RAD) group and an HIVD group without definite radiculopathy.

RESULTS

Fourteen patients had lumbosacral radiculopathies (RAD group) while 25 had no radiculopathy (HIVD group). No significant difference was found between the RAD and HIVD groups in TMA, PMA, and PMA/TMA. In terms of the criteria for the upper limit of IMA/UMA, 78.6% in the RAD group had an abnormal IMA/UMA ratio in at least 1 level, compared with 24% in the HIVD group and 10% in the control group. Thus, more cases with less muscle volume in the involved side were seen in the RAD group than in the HIVD and control groups.

CONCLUSION

Asymmetry of the multifidus muscles as seen in MRI was a useful finding to assess patients who had unilateral lumbosacral radiculopathy with HIVD. This may reflect the denervation of multifidus muscles in lumbosacral radiculopathy.