Postoperative outcomes and the association with overlap before or after the critical step of lumbar fusion.

Objective: This study assesses how degree of overlap, either before or after the critical operative portion, affects lumbar fusion outcomes.
Methods: The authors retrospectively studied 3799 consecutive patients undergoing single-level, posterior-only lumbar fusion over 6 years (2013-2019) at a university health system. Outcomes recorded within 30-90 and 0-90 postoperative days included emergency department (ED) visit, readmission, reoperation, overall morbidity, and mortality. Furthermore, morbidity and mortality were recorded for the duration of follow-up. The amount of overlap that occurred before or after the critical portion of surgery was calculated as a percentage of total beginning or end operative time. Subsequent to initial whole-population analysis, coarsened exact-matched cohorts of patients were created with the least and most amounts of either beginning or end overlap. Univariate analysis was performed on both beginning and end overlap exact-matched cohorts, with significance set at p < 0.05.
Results: Equivalent outcomes were observed when comparing exact-matched patients. Among the whole population, the degree of beginning overlap was correlated with reduced ED visits within 30-90 and 0-90 days (p = 0.007, p = 0.009; respectively), and less 0-90 day morbidity (p = 0.037). Degree of end overlap was correlated with fewer 30-90 day ED visits (p = 0.015). When comparing only patients with overlap, degree of beginning overlap was correlated with fewer 0-90 day reoperations (p = 0.022), and no outcomes were correlated with degree of end overlap.
Conclusions: The degree of overlap before or after the critical step of surgery does not lead to worse outcomes after lumbar fusion.