OBJECTIVE Pedicle subtraction osteotomy (PSO) is commonly performed for correction of spinal sagittal plane deformities. The PSO results in complex, multiple changes of the spinopelvic alignment. The influence of the variability of individual pelvic morphology has not been fully analyzed in previous outcome studies of sagittal imbalance. The aim of this study was to define radiological variables affecting the outcome after PSO in adult spinal deformities, with special emphasis on the variability of pelvic morphology. METHODS Clinical and radiographic outcomes were analyzed in a retrospective analysis of 104 patients who underwent a PSO at a single center. The radiographic variables studied were sagittal vertical axis (SVA), T1SPI (T-1 spinopelvic inclination), lumbar lordosis (LL), thoracic kyphosis (TK), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS). To control for the individual variation of pelvic morphology, the LL/PI, PT/PI, and SS/PI ratios were calculated. Clinical outcome was assessed using the visual analog scale for pain, Oswestry Disability Index, and EQ-5D preoperatively and at a minimum 1-year follow-up. Correlation coefficients were calculated between each individual radiographic variable and the outcome measures. The importance of LL mismatch to TK, reflecting the importance of a harmonious spine, was analyzed by comparing the outcome of patients with a TK+LL+PI ≤ 45° to those with a sum > 45°. RESULTS SVA and T1SPI demonstrated the strongest correlation with the clinical outcome scores (r = 0.4-0.5, p < 0.001). LL correlated weakly with the clinical outcome (r = 0.2-0.3, p < 0.003). Mismatch of LL to PI, however, did not correlate significantly with the outcome. Similarly, only weak and inconsistent correlation was observed between PT, SS, PT/PI, SS/PI, and functional outcome. Patients with a TK+LL+PI ≤ 45° had a significantly lower ODI score (33 vs 44) and a significantly higher EQ-5D score (0.64 vs 0.40) than patients with a sum > 45° (LL is a negative value). CONCLUSIONS PSO resulted in a substantial correction of sagittal imbalance and improved outcome in most patients in this study. Correction of the global sagittal balance appears to be a necessary precondition for a good outcome. A harmonious spine with a TK and an LL of similar magnitude seems to add to a positive outcome.
Keywords: ASD = adult spinal deformity; HRQOL = health-related quality of life; LL = lumbar lordosis; ODI = Oswestry Disability Index; PI = pelvic incidence; PSO = pedicle subtraction osteotomy; PT = pelvic tilt; SS = sacral slope; SVA = sagittal vertical axis; T1SPI = T-1 spinopelvic inclination; TK = thoracic kyphosis; VAS = visual analog scale; adult spine deformity; pedicle subtraction osteotomy; sagittal imbalance; spinopelvic parameters; surgical technique.