Arthroplasty versus internal fixation for displaced femoral neck fractures in older patients with dementia: a target trial emulation study

BACKGROUND AND PURPOSE: Target trial emulation can improve design transparency in observational comparative-effectiveness studies. We applied the framework to compare the outcome after arthroplasty with that of internal fixation (IF) in patients with dementia and displaced femoral neck fracture regarding recorded reoperation, mortality, length of stay, and postoperative mobility. METHODS: Using nationwide Danish registries, we emulated a target trial among patients aged ≥ 70 years. Patients were classified by index treatment (arthroplasty or IF) and analyzed according to the intention-to-treat estimand. Recorded reoperation in the Danish National Patient Registry within 365 days was the primary outcome. Secondary outcomes included major reoperation, mortality, length of stay, early mobilization, and mobility decline. Stabilized inverse probability of treatment weighting balanced measured covariates. We estimated weighted cumulative incidences accounting for competing death and weighted cause-specific hazard ratios (HRs) with 95% confidence intervals (CIs). RESULTS: The emulated target trial included 3,161 patients, of whom 2,231 received arthroplasty and 930 IF. At 365 days, recorded reoperation occurred in 298/2,231 vs 68/930 patients receiving arthroplasty or IF, respectively; weighted incidences were 13% (CI 13-14) vs 7.6% (CI 7.0-8.3) (HR 0.52, CI 0.39-0.69). Major reoperation occurred in 191/2,231 vs 68/930; weighted incidences were 8.6% (CI 8.2-8.9) vs 7.6% (CI 7.1-8.2) (HR 0.84, CI 0.63-1.10). Death occurred in 1,040/2,231 vs 421/930; weighted estimates were 47% (CI 46-48) vs 43% (CI 42-44) (HR 0.86, CI 0.77-0.98). Length of stay was modestly longer after arthroplasty, whereas early mobilization and postoperative mobility were similar. CONCLUSION: IF was associated with fewer recorded reoperations and lower mortality than arthroplasty in routine care. Active-comparator target trial emulation enabled a transparent comparison of the treatment strategies, but residual confounding and differential outcome ascertainment limited causal and clinical interpretation.