Five-Year Segment-Based Analysis of Radiographic and Symptomatic Adjacent Segment Disease Following Transforaminal Lumbar Interbody Fusion

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: To determine the 5-year incidence and risk factors of radiological adjacent segment disease (R-ASD) and symptomatic adjacent segment disease (S-ASD) after transforaminal lumbar interbody fusion (TLIF) using patient- and segment-based analyses. SUMMARY OF BACKGROUND DATA: Adjacent segment disease (ASD) remains a major concern after lumbar fusion surgery. Although previous studies have reported variable incidence rates, differences between R-ASD and S-ASD and segment-specific risk factors remain unclear. Particularly, evidence comparing cranial and caudal adjacent segments after TLIF with uniform mid-term follow-up is limited. METHODS: Patients who underwent TLIF at two institutions and completed a minimum 5-year follow-up were retrospectively reviewed. The study cohort consisted of 183 patients (mean age, 68.0±9.6 y). Patient-based and segment-based analyses were performed. Potential risk factors including demographic variables, and spinopelvic alignment parameters, preoperative adjacent segment status, and surgical interventions at adjacent levels, were evaluated. RESULTS: At 5-year follow-up, patient-based incidence of R-ASD and S-ASD was 31.1% and 18.6%. Segment-based analysis demonstrated that R-ASD occurred more frequently at the cranial segment than at the caudal segment (25.4% vs. 8.1%, P<0.001), whereas S-ASD incidence did not differ significantly. Multivariate analysis identified preoperative disc degeneration (OR 3.13, 95% CI 1.06-9.23) and additional decompression at the adjacent segment (OR 2.42, 95% CI 1.14-5.13) as independent risk factors for cranial R-ASD. Spinopelvic alignment parameters and preoperative foraminal stenosis were not significantly associated with the development of R-ASD and S-ASD. CONCLUSION: Segment-specific analysis revealed that cranial R-ASD is predominantly influenced by local degenerative changes and surgical intervention rather than global alignment parameters. Careful preoperative assessment of adjacent disc degeneration and cautious postoperative consideration of additional decompression may be important in surgical planning to mitigate ASD development after short-segment TLIF.