Pedicle Subtraction Osteotomy for Kyphosis Following Lumbar Fusion Surgery

INTRODUCTION: Pedicle subtraction osteotomy (PSO) is performed to correct sagittal plane deformity. This procedure is useful with revision cases in which the number of intact discs for correction is limited. METHODS: Forty-four patients (10 male and 34 female) with minimum follow-up of 2 years were reviewed; all had undergone PSO revision surgery for kyphosis following previous lumbar fusion surgery. The average age at operation was 72.8 years (range 42-85 years), and the average follow-up period was 4.1 years (2-9 years). The average fusion level was 7.5 (4-13 level), and the average previously fused level was 2.4 (1-7 level). RESULTS: The average operation time was 424 min, and average blood loss was 2880 g. The average JOA score of 14.0 before operation changed to 21.8 at 1-year follow-up and to 20.7 at final follow-up. The average recovery rate at final follow-up was 45.7%. Four patients underwent re-operations for proximal junctional kyphosis and 3 patients for rod fracture. The fusion rate was 88.6%, and 13 patients (29.5%) developed subsequent vertebral fracture. The average PI-LL (Pelvic incidence minus Lumbar lordosis) at pre-op of 52.9 degrees changed to 3.8 degrees at post-op, to 13.4 degrees at 1-year follow-up, and to 14.8 degrees at final follow-up. The average correction at the PSO site was 36.0 degrees at post-op, 36.7 degrees at 1-year follow-up, and 37.0 degrees at final follow-up. The average sagittal vertical axis at pre-op of 145.0 mm decreased to 51.2 mm at 1-year follow-up; however, it increased to 75.3 mm at final follow-up. CONCLUSION: PSO for correction of kyphosis following previous lumbar fusion surgery was an effective procedure without correction loss at the local osteotomy site; however, its surgical invasiveness and complication rate were high. Subsequent vertebral fracture, adjacent segment degeneration, and rod fracture contribute to deterioration of outcome that is evident at long-term follow-up.