Medical Student University of California, San Francisco San Jose, California, United States
Introduction: Pedicle subtraction osteotomy (PSO) is a powerful technique for surgical correction of sagittal imbalance. Comparative radiographic outcomes and rates of distal junctional pathology between PSO at L3 versus L4 have been under-reported.
Methods: A retrospective cohort study comparing patients that underwent either L3 or L4 PSO between 2005 and 2021 with at least 1-year radiographic follow-up was performed. Distal junctional pathology was defined as hardware failure or pseudarthrosis at or distal to the PSO level. Univariate and multivariate analyses were performed.
Results: A total of 117 patients met inclusion criteria; 87 (73.2%) patients underwent L3 PSO, and 30 (26.8%) underwent L4 PSO. Mean imaging follow-up length was 4.1 years (1.0-10.9 years). There were no significant differences in age, sex, BMI, operation time, and estimated blood loss between cohorts. Preoperatively, there were no significant differences in Hounsfield unit in sacrum and spinopelvic parameters, except L3 versus L4 PSO cohort had lower pelvic incidence (51.0±11.1 vs. 57.8±14.1, p=0.011). Postoperatively, there were no differences in primary rod diameter and metallic type, number of dual versus multi-rod constructs, graft materials, postoperative L5-S1 fusion, and PI-LL mismatch. L4 versus L3 PSO cohort had larger postoperative L4-S1 segmental lordosis (37.2±13.3 vs. 21.4±11.3 vs., p< 0.001) and reduced rates of low lordosis distribution index (LDI) (20.0% vs 58.6%, p< 0.001). The L4 versus L3 PSO cohort experienced lower rates of distal junctional pathology (16.7% vs. 49.4%, p=0.002), including hardware failure (42.5% vs. 16.7%, p=0.011) and pseudarthrosis (35.6% vs. 6.7%, p=0.002). Multivariate analysis confirmed that L4 PSO results in a 26% reduced risk of developing distal junctional pathology (OR 0.74, CI: 0.57 - 0.95).
Conclusion : L4 PSO had a lower rate of distal junctional pathology compared with L3 PSO. This could be related to more physiological distribution of lumbar lordosis by performing PSO at L4.
