Periprosthetic and interimplant femoral fractures: Biomechanical analysis

Abstract

The requirements for treatment of femoral fractures are increasing with the rising age of the patients. The aim of this study was to evaluate femoral stiffness and the fracture risk after inserting different implants and implant combinations. A total of 48 cadaveric femors were harvested and 8 groups were randomized on the basis of the bone mineral density (BMD). Different osteosyntheses following prosthetic stem implantation (hip and knee prostheses) were performed and compared with native femurs. All specimens were biomechanically tested in a four-point bending until fracture. The insertion of a femoral stem decreases the stiffness by approximately 33%. Ipsilateral retrograde nailing reduces the force to failure even more. This instable situation can be stabilized by a lateral locking compression plate. The most stable situation occurred in the presence of two cemented stems. Taken together these results clearly indicate that a hip prosthesis significantly weakens the femur, whereas two stems produce the most stable situation at all. The situation of a hip prosthesis and an retrograde nail should be avoided or covered by a bridging-osteosynthesis. In clinical practice an extramedullary fixation technique for distal femoral fractures should be preferred.