Biomechanical evaluation of peri- and interprosthetic fractures of the femur.
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.
Lehmann
Wolfgang
W
Department of Trauma, Hand, and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg 20246, Germany. wlehmann@uke.uni-hamburg.de
Rupprecht
Martin
M
Hellmers
Nils
N
Sellenschloh
Kai
K
Briem
Daniel
D
Püschel
Klaus
K
Amling
Michael
M
Morlock
Michael
M
Rueger
Johannes Maria
JM
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