ObjectiveOne of the primary goals of treatments received by elderly individuals (>= 75 years) with lumbar spine diseases is to improve their quality of life and obtain favorable outcomes (FOs). Predicting the risk of unfavorable outcomes (UFOs, defining as being unable to obtain functional independence and simultaneously being dissatisfied with the operation) will inform treatment decision-making and hospital resource allocation. However, optimal treatment strategy and accurate risk stratification for these patients remained largely unknown. MethodsConsecutive patients who underwent posterior lumbar interbody fusion or transforaminal lumbar interbody fusion from September 2018 to January 2021 were included in this study. Multivariate logistic regression analyses were performed to determine the independent predictors of UFOs at 6-month and 24-month follow-ups, respectively. Risk matrices and receiver operating characteristic curve were developed to visualize the cumulative effects of risk factors on UFOs at the 6-month and 24-month follow-ups. ResultsA total of 324 patients with a 6-month follow-up were recruited for this study. Of these, 67 patients experienced UFOs. A symptom duration > 12 months (OR 2.635, 95% CI 1.406-4.938, P = 0.002), fusion level >= 3 (OR 3.181, 95% CI 1.160-4.100, p = 0.015), the presence of major complications (OR 2.629, 95% CI 1.214-5.697, p = 0.014), and fat infiltration >= 50% (OR 2.150, 95% CI 1.155-4.005, p = 0.016) were independently correlated with UFOs at the 6-month follow-up. Similarly, A total of 241 patients with 24-month follow-up data were enrolled in this study. Among these patients, 86 experienced UFOs. A symptom duration > 12 months (OR 3.355, 95% CI 1.580-7.123, p = 0.002), PI-LL mismatch (OR 2.511, 95% CI 1.199-5.259, p = 0.015), fat infiltration >= 50% (OR 3.475, 95% CI 1.171-5.231, p = 0.018), and mECI > 5 (OR 4.836, 95% CI 1.217-6.610) were independently related to UFOs at the 24-month follow-up. Finally, using risk matrices and receiver operating characteristic curve, we visualized the cumulative impact of the respective four risk factors on the development of UFOs at 6-month and 24-month follow-ups. ConclusionIn this study, we found that there were differences in the reasons for UFOs between the 6-month and 24-month follow-ups. Our findings group patients along a spectrum of perioperative risks that inform care at an individual level.