Spinal deformity progression after posterior segmental instrumentation and fusion for idiopathic scoliosis

STUDY DESIGN Retrospective chart and radiographic review. PURPOSE To assess the incidence of and variables associated with spinal deformity progression after posterior segmental instrumentation and fusion at a single institution. Progression of the scoliotic deformity after posterior instrumented spinal fusion has been described. Recent studies have concluded that segmental pedicle screw constructs are better able to control deformity progression. METHODS Retrospective review of a consecutive series of idiopathic scoliosis patients (n = 89) with major thoracic curves (Lenke types 1-4) treated with posterior segmental instrumentation and fusion. Deformity progression was defined as a 10° increase in Cobb angle between the first-erect and 2-year post-operative radiographs. Clinical and radiographic data between the two cohorts (deformity progression versus stable) were analyzed to determine the variables associated with deformity progression. RESULTS Patients in the deformity progression group (n = 13) tended to be younger (median 13.7 vs. 14.7 years) and experienced a significant change in height (p = 0.01) during the post-operative period compared to the stable group (n = 76). At 2-years post-op, the patients in the deformity progression group had experienced a significantly greater change in upper instrumented vertebra (UIV) angulation, lower instrumented vertebra (LIV) angulation, and apical vertebral translation (AVT). Two-year post-op Scoliosis Research Society questionnaire (SRS-22) scores in the appearance domain were also significantly worse in the deformity progression group. Patients in the deformity progression group had a significantly greater difference between the lowest instrumented vertebra and stable vertebra compared to patients in the stable group (p = 0.001). CONCLUSIONS Deformity progression after posterior spinal fusion does occur after modern segmental instrumentation. Segmental pedicle screw constructs do not prevent deformity progression. Skeletally immature patients with a significant growth potential are at the highest risk for deformity progression. In immature patients, extending the fusion distally to the stable vertebra may minimize deformity progression. LEVEL OF EVIDENCE Level III.