Lumbar Apex Position as an Independent Risk Factor for Adjacent Segment Diseases in Patients Undergoing Short-Level Transforaminal Lumbar Interbody Fusion

Study Design. Retrospective study. Objective: To investigate whether lumbar apex position had an impact on the development of adjacent segment disease (ASD) following transforaminal lumbar interbody fusion (TLIF). Summary of Background Data. Previous studies have demonstrated that solely concentrating on lumbar lordosis value is not suitable, and neglecting the significance of lumbar apex can lead to mechanical complications. However, the relationship between lumbar apex and ASD is still not well understood. Methods. In this retrospective study, 234 consecutive patients who underwent L3-5 or L4-5 TLIF for degenerative diseases were reviewed. The study evaluated the associations between sagittal parameters and pelvic incidence (PI). Patients were labeled “matched” when lumbar apex position aligned with the theoretical target, and “mismatched” when it did not. Multivariate analysis was applied to find the independent risk factors of ASD. In addition, a focused subanalysis was performed based on the lumbar apex position (ideal match, cranial from ideal, and caudal from ideal). Results. After an average follow-up period of 70.6 months, 68 cases were identified as having ASD. Postoperatively, 64.7% (44 of 68) of the patients with ASD exhibited a mismatched lumbar apex, compared with 41% (68 of 166) of those without ASD ( P < 0.001). PI correlated significantly with proximal lordosis (PL) and lordosis distribution index (LDI) but not with distal lordosis (DL). Multivariate analysis identified age, L3–5 fusion, postoperative DL, and postoperative mismatched lumbar apex as independent risk factors of ASD. Upon the subanalysis, it was discovered that there were unique compensatory strategies in the cranial and caudal groups, with notable variations in postoperative DL, PL, and LDI among three groups (all P value of <0.05). Conclusion. Lumbar apex position significantly influenced the risk of ASD. To restore the lumbar apex to its ideal position, a proper value and distribution of DL should be attained. Level of Evidence. 4.