Lower mortality in distal femoral fractures in the presence of a knee arthroplasty: an observational study on 2,725 fractures from the Swedish Fracture Register

BACKGROUND AND PURPOSE: Distal femoral fractures (DFF) in older patients have mortality rates comparable to fractures of the proximal femur. An ageing population combined with an increasing number of patients undergoing total knee arthroplasty (TKA) will make periprosthetic distal femoral fractures (pDFF) more common. We investigated whether a pre-existing TKA influences mortality rates. PATIENTS AND METHODS: All patients ≥ 60 years registered in the Swedish Fracture Register with a DFF sustained between March 20, 2011 and December 31, 2020 were included. The study cohort comprised 2,725 patients, of which 650 had a pDFF. Unadjusted 90-day and 1-year mortality was estimated via Kaplan–Meier survival curves. A Cox regression model adjusted for age, sex, and treatment modality was used to investigate the association between DFF or pDFF and mortality. RESULTS: Mean age was 80 years and 82% were females. The most common injury mechanism was a simple fall (75%). The pDFF and DFF group were similar with regards to age, sex, and trauma mechanism. Unadjusted 90-day and 1-year mortality was 11% (95% CI 10–12) and 21% (CI 19–23), respectively. Kaplan–Meier survival analysis demonstrated a slightly lower mortality for pDFFs, especially in patients ≤ 70 years. The Cox regression model showed a lower hazard ratio (HR) for mortality in the pDFF group (HR 0.82, CI 0.71–0.94). INTERPRETATION: In a large cohort of patients ≥ 60 years with a distal femoral fracture, mortality rates at 90 days and 1 year post-injury were 11% and 21%, respectively. Periprosthetic fractures were associated with a lower mortality.