Beyond age and comorbidities: frailty and cognitive impairment are associated with early medical complications after surgery for lumbar spinal stenosis in patients aged 75 years and older.

BACKGROUND: Risk assessment before surgery for lumbar spinal stenosis in the very elderly relies largely on age and comorbidity scores. We asked: (1) is frailty (modified 5-item Frailty Index, mFI-5) associated with 30-day medical complications beyond age and comorbidity burden? (2) which geriatric parameters are independently associated? (3) is frailty associated with surgical complications? HYPOTHESIS: Frailty and specific geriatric impairments are more strongly associated with early medical complications than age or comorbidity indices. PATIENTS AND METHODS: Retrospective single-center observational cohort study of 143 consecutive patients aged 75 years and older operated on for lumbar spinal stenosis between 2016 and 2024 with a complete preoperative comprehensive geriatric assessment. The primary outcome was any medical complication within 30 days; secondary outcomes were surgical complications, transfusion, Clavien-Dindo grade and mortality. Patients were stratified as robust (mFI-5 0-1) or frail (≥ 2). RESULTS: Medical complications occurred in 54 patients (38%) and surgical complications in 43 (30%). Frail patients (n = 84) had more medical complications than robust patients (n = 59): 46% versus 25% (p = 0,014). No significant association was observed with surgical complications (25% versus 37%, p = 0,139). Neither age (p = 0,639) nor the Charlson index (p = 0,661) was associated with the primary outcome, whereas obesity (49% versus 32%, p = 0,047) and a lower MMSE (p = 0,006) were. In a multivariable model specified a priori (obesity, MMSE, mFI-5, fused levels), only the MMSE remained independently associated (OR 0,82 per point, 95% CI 0,72-0,94, p = 0,004); AUC 0,71 (95% CI 0,61-0,79), Hosmer-Lemeshow p = 0,28. Thirty-day mortality was 1,4%. DISCUSSION: Neither age nor comorbidity burden identified patients at risk of early medical decompensation, whereas frailty, obesity and cognitive status did. The dissociation between medical and surgical morbidity suggests frailty reflects systemic reserve rather than technical difficulty. These findings are hypothesis-generating and apply to patients already deemed eligible for surgery. LEVEL OF EVIDENCE: III; retrospective comparative cohort study.