Revision Free Loss of Sagittal Correction > 3 Years After Adult Spinal Deformity Surgery: Who and Why?

Abstract

Study designMulticenter retrospective cohort study.ObjectiveTo investigate risk factors for loss of correction within the instrumented lumbar spine following ASD surgery.Summary of background dataThe sustainability of adult deformity (ASD) surgery remains a health care challenge. Malalignment is a major reason for revision surgery.Methods321 patients who underwent fusion of the lumbar spine (≥5 levels, LIV pelvis) with a revision-free follow-up ≥3 years were identified. Patients were stratified by change in PI-LL from 6 weeks to 3 years postop as Maintained vs. Loss >5°. Those with instrumentation failure (broken rod, screw pullout, etc.) were excluded before comparisons. Demographics, surgical data, and radiographic alignment were compared. Repeated measure ANOVA was performed to evaluate the maintenance of the correction for L1-L4 and L4-S1. Multivariate logistic regression was conducted to identify independent surgical predictors of correction loss.ResultsThe cohort had a mean age of 64 yrs, mean BMI 28 kg/m 2 , 80% female. 82 patients (25.5%) lost >5° of PI-LL correction (mean loss 10±5°). After exclusion of patients with instrumentation failure, 52 Loss were compared to 222 Maintained. Demographics, osteotomies, 3CO, IBF, use of BMP, rod material, rod diameter, and fusion length were not significantly different. L1-S1 screw orientation angle was 1.3±4.1 from early postop to 3 years ( P =0.031), but not appreciably different at L4-S1 (-0.1±2.9 P =0.97). Lack of a supplemental rod (OR 4.0, P =0.005) and fusion length (OR 2.2, P =0.004) were associated with loss of correction.ConclusionsApproximately a quarter of revision-free patients lose an average of 10° of their 6-week correction by 3 years. Lordosis is lost proximally through the instrumentation (i.e. tulip/shank angle shifts and/or rod bending). The use of supplemental rods and avoiding sagittal overcorrection may help mitigate this loss.