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.