The Role of Paraspinal Muscle in Postoperative Coronal Balance Transition in Degenerative Lumbar Scoliosis

STUDY DESIGN: Retrospective observational study. OBJECTIVE: The purpose of this study was to determine whether paraspinal muscle could influence postoperative coronal balance and its transition in degenerative lumbar scoliosis (DLS). SUMMARY OF BACKGROUND DATA: Although the importance of the paraspinal muscles (PSM) in sagittal alignment is well recognized, there is no information about its role in coronal balance. METHODS: The study included 102 DLS patients. Evaluation of the PSM on magnetic resonance imaging were conducted at baseline. Coronal measurements included coronal balance distance (CBD), major Cobb angle, L4 coronal tilt, and L5 coronal tilt. The cohort was divided based on postoperative parameters into persistent coronal balance (PCB), worsened coronal imbalance (WCIB), recurrent coronal balance (RCB), and persistent coronal imbalance (PCIB) according to immediate postoperative and follow-up coronal balance. Multivariate logistic regression models for postoperative CIB, follow-up WCIB and follow-up RCB were utilized to identify statistically significant associations while accounting for confounders. RESULTS: The cohort was divided into 57 with PCB, 13 with WCIB, 10 with RCB, and 22 with PCIB. The follow-up groups with CIB exhibited more severe fatty infiltration in the extensor muscle compared with the balanced groups. Specifically, the WCIB group demonstrated the most severe extensor muscle degeneration, particularly on the concave sides, and the most prominent asymmetric degeneration of the PSM among the four groups. Furthermore, patients with CIB had worse sagittal malalignment compared with those with CB at the last follow-up. CONCLUSIONS: Patients exhibiting stronger extensor muscle mass were prone to immediate postoperative CB and more likely to experience spontaneous improvement or recurrence of coronal balance during follow-up. Severe extensor muscle degeneration and prominent asymmetric bilateral PSM degeneration represent potential risk factors for persistent CIB and recurrent CIB. It is crucial to assess the dynamic change during the follow-up period as long-term prognosis may be impacted if CB deteriorates, or otherwise develops during follow-up. LEVEL OF EVIDENCE: 3.