Long‐term influence of paraspinal muscle quantity in adolescent idiopathic scoliosis following deformity correction by posterior approach

Pedicle screw instrumentation (PSI) through posterior approach has been the mainstay of deformity correction for adolescent idiopathic scoliosis (AIS). However, changes in the quantity of paraspinal muscles after AIS surgery has remained largely unknown. The aim of this study was to investigate long‐term follow‐up changes in paraspinal muscle volume in AIS surgery via a posterior approach. Forty‐two AIS patients who underwent deformity correction by posterior approach were analyzed through a longitudinal assessment of a cross‐sectional area (CSA) in paraspinal muscles with a minimum five‐year follow‐up. The CSA were measured using axial computed tomography images at the level of the upper endplate L4 by manual tracing. The last follow‐up CSA ratio of the psoas major muscle (124.5%) was significantly increased compared to the preoperative CSA ratio (122.0%) (p < 0.005). The last follow‐up CSA ratio of the multifidus and erector spine muscles significantly decreased compared to the preoperative CSA ratio (all p < 0.005). The CSA ratio of the erector spine muscle was correlated with the CSA ratio of the psoas major (correlation coefficient = 0.546, p < 0.001). Therefore, minimizing the injury to the erector spine muscle is imperative to maintaining psoas major muscle development in AIS surgery by posterior approach.