Purpose: The purpose of this study was to analyse the incidence of interprosthetic femoral fractures and describe risk factors for them.
Methods: Between 2009 and 2015, we selected patients who were carrying two implants (hip and knee) in the same femur. We collected demographic and clinical data and performed a radiological evaluation to analyse the gap between implants-the femoral canal area and total femoral area-in the axial plane. We defined interprosthetic fracture as that corresponding to a Vancouver type C fracture and types 1 and 2 according to the Su classification.
Results: We studied 68 patients who had total knee arthroplasty (TKA), and 44 patients who had total hip arthroplasty (THA); 24 patients an intramedullary nail. We found six interprosthetic fractures (8.8 %), all in patients with a non-cemented THA. There was a tendency towards statistical difference (p = 0.08). Patients with an additional implant at the proximal femur were statistically less likely to have an interprosthetic fracture (p = 0.04). In radiological results, we found more interprosthetic fractures in patients who had an increased femoral canal area in the axial plane just distal to the tip of the hip implant.
Conclusions: Identifying risk factors for this specific type of fracture may facilitate their prevention. Better implant stability and the presence of a gap between stems in a lower canal zone appear to hinder the occurrence of interprosthetic fractures.
Keywords: Femoral gap fracture; Interimplant fracture; Interprosthetic fracture; Ipsilateral femoral implants; Periprosthetic fracture.