title: What is the risk of stress risers for interprosthetic fractures of the femur? A biomechanical analysis.
abstract: OBJECTIVE
  Due to increasing life expectancy we see a rising number of joint replacements. Along with the proximal prosthesis in the femur, more and more people have a second implant on the distal ipsilateral side. This might be a retrograde nail or a locking plate to treat distal femur fractures or a constrained knee prosthesis in the case of severe arthrosis. All these constructs can lead to fractures between the implants. The goal of this study was to evaluate the risk of stress risers for interprosthetic fractures of the femur.
  
  
  METHODS
  Thirty human cadaveric femurs were divided into five groups: (1) femurs with a prosthesis on the proximal side only, (2) hip prosthesis on the proximal end and a distal femur nail, (3) femurs with both a hip prosthesis and a constrained knee prosthesis, (4) femurs with a hip prosthesis on the proximal side and a 4.5-mm distal femur locking plate; the locking plate was 230 mm in length, with ten holes in the shaft, and (5) femurs with a proximal hip prosthesis and a 4.5-mm distal femur locking plate; the locking plate was 342 mm in length, with 16 holes in the shaft.
  
  
  RESULTS
  Femurs with a hip prosthesis and knee prosthesis showed significantly higher required fracture force compared to femurs with a hip prosthesis and a distal retrograde nail. Femurs with a distal locking plate of either length showed a higher required fracture force than those with the retrograde nail.
  
  
  CONCLUSIONS
  The highest risk for a fracture in the femur with an existing hip prosthesis comes with a retrograde nail. A distal locking plate for the treatment of supracondylar fractures leads to a higher required fracture force. The implantation of a constrained knee prosthesis that is not loosened on the ipsilateral side does not increase the risk for a fracture.
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246, Hamburg, Germany. wlehmann@uke.de
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lehmann
authors.forename: Martin
authors.initials: M
authors.lastname: Rupprecht
authors.forename: Jacob
authors.initials: J
authors.lastname: Nuechtern
authors.forename: Daniel
authors.initials: D
authors.lastname: Melzner
authors.forename: Kai
authors.initials: K
authors.lastname: Sellenschloh
authors.forename: Jan
authors.initials: J
authors.lastname: Kolb
authors.forename: Florian
authors.initials: F
authors.lastname: Fensky
authors.forename: Michael
authors.initials: M
authors.lastname: Hoffmann
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.forename: Michael
authors.initials: M
authors.lastname: Morlock
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Rueger
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001858:Bone Nails / Q000009:adverse effects; D001860:Bone Plates / Q000009:adverse effects; D002102:Cadaver; D005260:Female; D005264:Femoral Fractures / Q000209:etiology*; D006622:Hip Prosthesis / Q000009:adverse effects; D006801:Humans; D007720:Knee Prosthesis / Q000009:adverse effects; D008297:Male; D057068:Periprosthetic Fractures / Q000209:etiology*; D012307:Risk Factors; D013314:Stress, Mechanical