Sarcopenia and Back Muscle Degeneration as Risk Factors for Degenerative Adult Spinal Deformity with Sagittal Imbalance and Degenerative Spinal Disease: A Comparative Study

BACKGROUND: Many factors affect spinal alignment in adult spinal deformity with sagittal imbalance. However, although the importance of the paravertebral muscle and ligamentum complex in proper spinal alignment is well recognized, little information is available regarding the role of the paravertebral muscles in maintaining sagittal spinal alignment. METHODS: A total of 108 patients who had visited our institution from January 2016 to June 2018 were included in the present study. The patients were categorized as follows: degenerative adult spinal deformity with sagittal imbalance group and degenerative spinal disease group. The appendicular skeletal muscle mass index and handgrip strength of each patient were measured to evaluate for sarcopenia. Computed tomography was used to measure the cross-sectional area (CSA) and fat infiltration rate to evaluate paravertebral muscle morphology. The paravertebral muscle function was assessed by measuring the lumbar flexor strength and lumbar extensor strength using a lumbar isokinetic dynamometer. RESULTS: The degenerative adult spinal deformity with sagittal imbalance group had a lower CSA index and lumbar extensor strength index and higher fat infiltration rate than the degenerative spinal disease group. No statistically significant differences in the appendicular skeletalmusclemass index and handgrip strength were found between the 2 groups. Only the CSA showed a correlation with the radiological parameters, such as pelvic tilt and lumbar lordosis. CONCLUSIONS: Degeneration of the paravertebral muscle is a risk factor for degenerative adult spinal deformity with sagittal imbalance but not for sarcopenia. Thus, spinal sagittal imbalance is affected by isolated paravertebral muscle degeneration rather than by systemic muscle degeneration.