Preventing adjacent segment disease after lumbar fusion: a new perspective emphasizing individualized factors.

Background: Although posterior lumbar interbody fusion (PLIF) is effective in treating degenerative lumbar spine diseases, postoperative adjacent segment disease (ASD) significantly affects long-term prognosis and quality of life. The complex pathogenesis may involve systemic inflammation, lumbar muscle degeneration, biomechanical changes, and surgical factors, but comprehensive studies are lacking. The aim of this study was to analyze the risk factors for ASD following PLIF and to provide guidance for clinical prevention and management. Methods: A retrospective analysis was conducted on 500 patients who underwent PLIF from January 2017 to August 2022. Patients were divided into a non-ASD group (n=404) and an ASD group (n=96) based on postoperative imaging. Functional outcomes were assessed using the visual analog scale and the Oswestry Disability Index (ODI). Univariate and multivariate logistic regression analyses examined factors such as neutrophil-to-lymphocyte ratio (NLR), psoas major muscle index (PMI), multifidus muscle index (MMI), multifidus muscle fat infiltration rate (MFI), cage subsidence, pelvic incidence-lumbar lordosis mismatch, and nonunion to identify independent risk factors for ASD. Results: The incidence of ASD was 19.2%. Postoperative visual analog scale and ODI scores improved significantly in both groups, but the non-ASD group experienced a greater degree of pain relief and functional recovery. Elevated NLR, decreased PMI and MMI, increased MFI, cage subsidence, lower Hounsfield units (HU) values, and nonunion were identified as independent risk factors for ASD. Conclusions: ASD after PLIF is closely associated with systemic inflammation, lumbar muscle degeneration, cage subsidence, and nonunion. Interventions targeting these risk factors-such as optimizing inflammatory status preoperatively, enhancing lumbar muscle rehabilitation, improving surgical techniques to prevent cage subsidence, and promoting bone fusion-may reduce the incidence of ASD and improve long-term outcomes.