• Wolfgang Lehmann, Martin Rupprecht, Jacob Nuechtern, Daniel Melzner, Kai Sellenschloh, Jan Kolb, Florian Fensky, Michael Hoffmann, Klaus Püschel, Michael Morlock, and Johannes M Rueger.
• Department of Trauma, Hand and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246, Hamburg, Germany. wlehmann@uke.de
• Int Orthop. 2012 Dec 1;36(12):2441-6.

PurposeDue 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.MethodsThirty 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.ResultsFemurs 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.ConclusionsThe 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.

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