title: Biomechanical evaluation for mechanisms of periprosthetic femoral fractures.
abstract: BACKGROUND
  There are a number of biomechanical tests for various treatment options of periprosthetic femoral fractures, but different loading modalities prelude their direct comparison. This study was designed to develop an experimental model of osteoporotic bone fractures near the femoral stem that is based on a simple testing protocol to increase the reproducibility. In addition, we wanted to clarify whether a femoral prosthetic stem reduces the femoral fracture strength.
  
  
  METHODS
  Twenty human cadaveric femurs were harvested, and five groups were randomized on the basis of the bone mineral density using a pQCT device. The specimens of three groups were provided with a cemented Exeter V40 stem and loaded to failure with torsion (I), anterior (II), and lateral load (III). The femurs of groups IV and V remained uninstrumented and were tested in a four-point bending assay similar to groups II and III. All biomechanical testings were realized with a servohydraulic testing machine (MTS).
  
  
  RESULTS
  There was no significant difference regarding bone mineral density of all groups. Torsional testing generated proximal intertrochanteric fractures and anterior loading resulted exclusively in supracondylar fractures. Introducing the force from the lateral side, all fracture lines occurred close to the tip of the stem, similar to a Vancouver-B fracture. Assuming that lateral load application is a main responsible mechanism of periprosthetic femoral fracture near the tip of the stem, the fracture strength of instrumented femurs was significantly reduced (group III: 4,692 N vs. group V: 6,931 N; p < 0.05).
  
  
  CONCLUSIONS
  Prosthetic stems reduce femoral fracture strength significantly. In an osteoporotic bone model, a four-point bending test with lateral load application seems to be a suitable approach.
authors: Department of Trauma-, Hand-, and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors: Martin
authors: M
authors: Rupprecht
authors: Kai
authors: K
authors: Sellenschloh
authors: Lars
authors: L
authors: Grossterlinden
authors: Klaus
authors: K
authors: Püschel
authors: Michael
authors: M
authors: Morlock
authors: Michael
authors: M
authors: Amling
authors: Johannes M
authors: JM
authors: Rueger
authors: Wolfgang
authors: W
authors: Lehmann