Imbalance of muscles around the cervical spine in patients with degenerative cervical spondylotic kyphosis and myelopathy.

Background: To measure the muscle strength around the cervical spine; clarify the relationships among muscles, cervical sagittal alignment, and cervical spondylotic myelopathy(CSM); and understand the process underlying loss of cervical lordosis.

Methods: Sex, age, course of illness, and radiological data were obtained for patients with CSM and a control group of healthy individuals. C2-7 Cobb angles were measured in cervical radiographs, and the vertebral body areas(VBAs) and cross-sectional areas(CSAs) of the deep flexors, superficial flexors(SF), deep extensors, and superficial extensors(SE) were measured from the C3/4 to C6/7 intervertebral levels in T2-weighted axial magnetic resonance images. The CSA/VBA ratio was compared among CSM patients with and without degenerative cervical kyphosis(DCK) and control group RESULTS: Patients with CSM, especially those with DCK, showed an imbalance of muscles around the cervical spine. The CSA/VBA ratios of SF/SE at the C3/4 level(P=0.036), total flexors(TF)/total extensors(TE) at the C6/7 level(P=0.006), total deep muscles(TD)/total superficial muscles(TS) at the C4/5 level(P=0.004), and TD/TS at the C6/7 level(P=0.031) differed significantly among the three groups. The CSM with DCK group tended to show larger CSA/VBA ratios of flexors/extensors and superficial muscles/deep muscles.

Conclusions: The greater strength of the flexors relative to the extensors and the superficial muscles compared with the deep muscles plays a role in pathogenesis of CSM with DCK, indicating the importance of neck and shoulder muscle-strengthening exercises in patients showing CSM with DCK.