Radiographic Predictors for Mechanical Failure After Adult Spinal Deformity Surgery

Study Design. Retrospective cohort study at a single institution. Objective. We aimed at estimating the rate of revision procedures and identify radiographic predictors of mechanical failure after adult spinal deformity surgery. Summary of Background Data. Mechanical failure rates after adult spinal deformity surgery range 12% to 37% in literature. Although the importance of spinal and spino-pelvic alignment is well documented for surgical outcome and ideal alignment has been proposed as sagittal vertical axis (SVA) < 5 cm, pelvic tilt < 20 degrees and lumbar lordosis (LL) = pelvic incidence +/- 9 degrees, the role of radiographic sagittal spine parameters and alignment targets as predictors for mechanical failure remains uncertain. Methods. A consecutive cohort of adult spinal deformity patients who underwent corrective surgery with at least 5 levels of instrumentation between January 2008 and December 2012 at a single tertiary spine unit were followed for at least 2 years. Time to death or failure was recorded and cause-specific Cox regressions were applied to evaluate predictors for mechanical failure or death. Results. A total of 138 patients with median age of 61 years were included for analysis. Follow up ranged 2.1 to 6.8 years. In total 47% had revision and estimated failure rates were 16% at 1 year increasing to 56% at 5 years. A multivariate analysis adjusting for age at surgery showed increased hazard of failure from LL change > 30 degrees, postoperative TK > 50 degrees, and SS <= 30 degrees. LL change was mostly because of 3-column osteotomy and ending the instrumentation at L5 or S1 increased the hazard of failure more than 6 fold compared with more cranial lumbar levels. Conclusion. Mechanical failure rate was 47% after adult spinal deformity corrective surgery. LL change > 30 degrees, postoperative TK > 50 degrees, and postoperative SS <= 30 degrees were independent radiographic predictors associated with increased hazard of failure.