Frailty and bone quality as the predictors of mechanical complications for patients after lumbar interbody fusion: a retrospective cohort study

Mechanical complications following lumbar interbody fusion are common in in elderly patients, particularly those with compromised bone quality. The MRI-based vertebral bone quality (VBQ) score assesses bone quality, while the modified frailty index (mFI) captures systemic physiological reserve. This study aimed to evaluate the independent and combined predictive value of VBQ and mFI for mechanical complications. A retrospective cohort study was conducted on 132 patients who underwent lumbar interbody fusion with at least 3-year follow-up. VBQ score was calculated from preoperative T1-weighted MRI, and mFI was derived from 11 comorbidities, with frailty defined as mFI ≥ 0.27. Mechanical complications were assessed on radiographs and CT. Multivariable logistic regression and receiver operating characteristic (ROC) curve analysis were performed. Mechanical complications occurred in 20 patients (15.2%). Compared with patients without complications, those with complications had significantly higher age, frailty proportion, and VBQ scores (all P < 0.05). Multivariable analysis showed that both frailty (OR 3.657, 95% CI 1.035–12.916, P = 0.044) and VBQ score (OR 7.128, 95% CI 1.838–27.643, P = 0.005) independently predicted complications. The combined model (VBQ + mFI) achieved an area under the curve (AUC) of 0.765 (95% CI 0.655–0.874), outperforming VBQ alone (AUC 0.689) and mFI alone (AUC 0.647). Both frailty and poor bone quality independently predict mechanical complications after lumbar interbody fusion. A combined model integrating VBQ and mFI provides potentially improved risk stratification, suggesting the importance of preoperative assessment of both skeletal and physiological reserve in high-risk patients.