title: Biomechanical evaluation of peri- and interprosthetic fractures of the femur.
abstract: BACKGROUND
  Because of an increasing life expectancy of patients and the rising number of joint replacements, peri- and interprosthetic femoral fractures are a common occurrence in most trauma centers. This study was designed to answer two primary questions. First, whether the fracture risk increases with two intramedullary implants in one femur; and second, whether a compression plate osteosynthesis is sufficient for stabilizing an interprosthetic fracture.
  
  
  METHODS
  Twenty-four human cadaveric femurs were harvested and four groups were matched based on the basis of bone density using a peripher quantitative computer tomography (pQCT). All groups-(I) hip prosthesis with a cemented femoral stem; (II) hip prosthesis and retrograde femoral nail; (III) hip prosthesis, retrograde femoral nail, and lateral compression plate; (IV) all three implants with an additional simulated interprosthetic fracture-were biomechanically tested in a four-point bending in lateral-medial direction.
  
  
  RESULTS
  The second group with two intramedullary implants exhibited 20% lower fracture strength in comparison with group 1 with proximal femoral stem only. The stabilization of an interprosthetic fracture with a lateral compression plate (group IV) resulted in a fracture strength similar to femur with prosthesis only.
  
  
  CONCLUSIONS
  Two intramedullary implants reduce the fracture strength significantly. If an interprosthetic fracture occurs, sufficient stability can be achieved by a lateral compression plate. Because two intramedullary implants in the femur may decrease the fracture strength, the treatment of supracondylar femoral fractures with a retrograde nail in cases with preexisting ipsilateral hip prosthesis should be reconsidered.
authors.affiliation: Department of Trauma, Hand, and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg 20246, Germany. wlehmann@uke.uni-hamburg.de
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lehmann
authors.forename: Martin
authors.initials: M
authors.lastname: Rupprecht
authors.forename: Nils
authors.initials: N
authors.lastname: Hellmers
authors.forename: Kai
authors.initials: K
authors.lastname: Sellenschloh
authors.forename: Daniel
authors.initials: D
authors.lastname: Briem
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.forename: Michael
authors.initials: M
authors.lastname: Amling
authors.forename: Michael
authors.initials: M
authors.lastname: Morlock
authors.forename: Johannes Maria
authors.initials: JM
authors.lastname: Rueger
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D001696:Biomechanical Phenomena; D015519:Bone Density; D001858:Bone Nails; D001860:Bone Plates; D002102:Cadaver; D005260:Female; D005264:Femoral Fractures / Q000503:physiopathology*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D014057:Tomography, X-Ray Computed