[An in vitro model for producing femoral fractures and for the study of primary stability of cerclage].
OBJECTIVE
Intraoperative femoral fracture is a well recognized intraoperative complication of cementless total hip arthroplasty (THA). This study was designed to establish an in-vitro model for initiation of fractures of the femur in cementless THA and to assess the effect of fracture fixation by cerclage wiring using steel wire (Protasul).


METHODS
Ten human femur specimens were studied. Longitudinal cracks were created by pressing a well fixed conical stem deeper into the femur in a material testing machine.


RESULTS
The force necessary to propagate a longitudinal crack in the femur was 1915 N to 9288 N (median 6531 N). This forces are according to 3 to 15 times (median 11 times) body weight. There was no difference of force between left and right femurs from the same individual (U-test). The femoral cortex fractured in 5 cases ventrally, in 6 cases medially and in 1 case laterally. After monofile cerclage wire application the force required to press prosthesis 5 mm deeper into the medullary canal was 0.3 to 2.7 times body weight. After monofile cerclage wire application pressing in the prosthesis 30 mm needed 1.8 to 8.1 times body weight.


CONCLUSIONS
During insertion of a conical stem the orthopaedic surgeon should look for fractures of the medial cortex of the femur which is the most frequent location for fractures. This in-vitro model provides a reproductable method for the initiation and propagation of longitudinal femoral fractures in press-fit noncemented THA system and to assess the effect of fracture fixation in the form of cerclage wiring.
Carls
J
J
Orthopädische Klinik, Medizinischen Hochschule Hannover im Annastift e.V.
Kohn
D
D
Kirsch
L
L
Carls
G
G
D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D001696:Biomechanical Phenomena; D001864:Bone Wires; D005260:Female; D005264:Femoral Fractures / Q000503:physiopathology / Q000601:surgery*; D005269:Femur / Q000503:physiopathology; D005593:Fracture Fixation, Internal / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D007431:Intraoperative Complications / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D016474:Weight-Bearing / Q000502:physiology
Ein in-vitro Modell zur Erzeugung von Femurfrakturen und zur Untersuchung der Primärstabilität von Cerclagen.