Degenerative characteristics of multifidus at different vertebral levels of scoliosis in patients with degenerative lumbar scoliosis and relationship of these degenerative characteristics with surface electromyography activity

BACKGROUND: Previous studies have investigated the imaging changes of the paravertebral muscles (PVM) in patients with degenerative lumbar scoliosis (DLS); however, most of these studies focused on the apical vertebra (AV) level or compared with the average of the whole-segment measurement. In this study, magnetic resonance imaging (MRI) combined with surface electromyography (sEMG) was used to analyze the degenerative characteristics of the multifidus (MF) in patients with DLS at three levels of scoliosis (upper end vertebra [UEV], AV, and lower end vertebra [LEV]). METHODS: This is a prospective cross-sectional study. Forty patients with DLS (DLS group) and 40 healthy individuals without lumbar scoliosis (control group) were evaluated. The percentage of fat infiltration area (%FIA) and muscle relative cross-sectional area (rCSA) of the MF at the three levels of scoliosis were measured on MRI, whereas the sEMG activity of the participants in both groups was recorded during action tasks. The imaging parameters, sEMG activity, and relationship between them were analyzed. RESULTS: In the control group, there were no significant differences in the %FIA, rCSA, or sEMG activation of the MF between the bilateral sides at the three measured levels. In the DLS group, measurement of the MF at the UEV and AV levels showed that the %FIA was larger on the concave than convex side and that the rCSA was smaller on the concave than convex side, but there was no difference between the two parameters at the LEV level. In the standing flexion and extension tasks, the sEMG activation of the MF was higher on the concave than convex side. The coronal Cobb angle was correlated with the difference in the measurement data of the MF at the UEV and AV levels, but not with the difference at the LEV level. CONCLUSION: The MF in patients with DLS has the same degenerative features at the UEV and AV levels, with the concave side showing greater degeneration; however, there are different degenerative manifestations at the LEV level. The MF degeneration at the UEV and AV levels is the result of spinal deformity, while the muscle changes at the LEV level are more consistent with natural degeneration.