Interimplant femoral fractures: a heterogeneous fragility injury Fracture patterns, management, and outcomes of a consecutive series

Abstract Purpose Interimplant femoral fractures occur between two preexisting femoral implants and, beyond interprosthetic fractures, remain poorly defined. We analyzed their characteristics, management, and outcomes, and propose a classification encompassing all implant combinations. Methods This retrospective single-center study included interimplant fractures treated from July 2013 to August 2025, with one-year follow-up. Fractures were classified by proximal and distal implant position as intramedullary (I) or extramedullary (E): II, IE, EI, and EE. Primary outcomes were one-year mortality and local complications. Results Forty-six fractures in 45 patients were included (median age 87.0 years; 89.1% female). Interprosthetic fractures represented 45.7% and IE fractures 73.9%. A compromised proximal implant was present in 28 of 40 fractures (70.0%) with an intramedullary proximal implant and in none of the 6 with an extramedullary one (p < 0.01), whereas a distal intramedullary implant was associated with a shorter implant gap (78.0 vs 209.2 mm, p < 0.01). Fixation alone was performed in 76.1%, revision-based procedures in 17.4%, and nonoperative management in 6.5%, regardless of fracture subtype (p = 0.77) or implant compromise (p = 0.40). Revision procedures required longer surgical time (195.0 vs 127.0 minutes, p < 0.01) and had more local complications (50.0% vs 11.4%, p = 0.03), mainly mechanical, even after stratification by subtype (p = 0.04). One-year mortality was 19.6%, and 15.2% returned home. Conclusion Interimplant femoral fractures are heterogeneous fragility injuries with high mortality and functional decline. The proposed classification identifies distinct biomechanical patterns, and fixation alone appears preferable whenever implant stability allows it.