Interimplant femoral fracture: analysis of risk factors

Interimplant fractures present a significant challenge for orthopedic surgeons. Despite a noticeable rise in these cases in recent years, our understanding of this specific fracture type remains limited. This study aims to analyze and identify the primary risk factors associated with interimplant femoral fractures. We conducted a retrospective analysis involving 20 patients with interimplant femoral fracture (case group) and 18 patients who had both proximal and distal femoral implants but did not experience interimplant fractures (control group). Our analysis focused on demographic factors (age, sex, BMI) and radiographic parameters (implant types, gap between implants, cortical thickness, femoral canal area) to identify potential risk factors. In the case group, all patients were females, whereas in the control group, 16 patients were female and 2 were males. The mean age in the case group was 88 \(\pm \) $\pm$ 9 years and in the control group was 87 \(\pm \) $\pm$ 12 years. None of the demographic differences reached statistical significance. The mean cortical thickness in the case group was 6 \(\pm \) $\pm$ 2.25 mm, whereas in the control group, it was 9 \(\pm \) $\pm$ 1.75 mm (p-value < 0.001). The median gap between the proximal and distal tips of the implants measured 194 \(\pm \) $\pm$ 126 mm in the case group and 66 \(\pm \) $\pm$ 78 mm in the control group (p-value < 0.001). Additionally, the mean femoral canal area was 284 \(\pm \) $\pm$ 102 mm² in the case group and 227 \(\pm \) $\pm$ 26 mm² in the control group (p-value < 0.010). Our data indicate that a small cortical thickness, a wide femoral canal area, and having a hip arthroplasty despite a gap between the implants exceeding 110 mm are factors that elevate the risk of interimplant femoral fracture. Notably, osteoporosis therapy emerges as a protective factor against these fractures.