Incidence Rates and Risks for Reoperations for Nonunion and Adjacent Level Disease

Study Design. A retrospective cohort study. Objective. To determine whether there is a difference in reoperations for adjacent segment disease (operative ASD) and nonunion (operative nonunion) in lumbar fusions that stop at T10/T11/T12 versus L1. Summary of Background Data. Current lumbar spine surgery is based on the belief that ASD occurs if fusions are stopped at L1 although there is varying evidence to support this assumption. Methods: We conducted a cohort study using data from a US-based integrated health care system’s Spine Registry of adult patients older than or equal to 18 years with degenerative disc disease/adult lumbar deformity who underwent primary lumbar fusions. The exposure of interest was lumbar fusions stopping at L1 versus T10/T11/T12. Propensity score-weighted Cox proportional hazards regressions were used to evaluate reoperation risk for ASD and for nonunion. Results. The study cohort included 227 lumbar fusions that stop at L1 and 228 stop at T10/T11/12. The mean age for the cohort was 68.4 years with a mean follow-up time of 6.3 years. For caudal level at L5 and S1, we found no statistical differences between operative ASD stopping at L1 versus T10/11/12 (HR = 1.03, 95% CI = 0.53–2.02, P = 0.93 and HR = 0.67, 95% CI = 0.27–1.67, P = 0.39, respectively). For the Short-segment fusions (caudal level: L3, 4, 5) and Long-segment fusions (L5, S1. S1+ilium) we also found no statistical difference in operative ASD (HR = 1.44, 95% CI = 0.68–3.09, P = 0.34 and HR = 0.83, 95% CI = 0.52–1.30, P = 0.41, respectively). For Long-segment fusions we also found no statistical difference in operative nonunion (HR = 0.65, 95% CI = 0.20–2.11, P = 0.47). Conclusion. Our study provides some evidence against crossing the thoracolumbar junction (TLJ) for individual constructs terminating at S1, and for Long-segment fusions, based on comparisons of operative ASD and operative nonunion. However, further research is needed to determine whether this finding holds true for individual constructs with caudal levels at L2, L3, L4, and S1+ilium.