Asymmetric atrophy of paraspinal muscles in patients with chronic unilateral lumbar radiculopathy

Objective To assess the cross-sectional area (CSA) of the muscles for investigating the occurrence of asymmetry of the paraspinal (multifidus and erector spinae) and psoas muscles and its relation to the chronicity of unilateral lumbar radiculopathy using magnetic resonance imaging (MRI).Methods This retrospective study was conducted between January 2012 to December 2014. Sixty one patients with unilateral L5 radiculopathy were enrolled: 30 patients had a symptom duration less than 3 months (group A) and 31 patients had a symptom duration of 3 months or more (group B). Axial MRI measured the CSA of the paraspinal and psoas muscles at the middle between the lower margin of the upper vertebra and upper margin of the lower vertebra, and obtained the relative CSA (rCSA) which is the ratio of the CSA of muscles to that of the lower margin of L4 vertebra.Results There were no differences in the demographics between the two groups. In group B, rCSA of the erector spinae at the L4-5 level, and that of multifidus at the L4-5 and L5-S1 levels, were significantly smaller on the involved side as compared with the uninvolved side. In contrast, no significant muscle asymmetry was observed in group A. The rCSA of the psoas was not affected in either group.Conclusion The atrophy of the multifidus and erector spinae ipsilateral to the lumbar radiculopathy was observed only in patients suffering from unilateral radiculopathy for 3 months or more.