A comparative study of two cerclage systems.

Intraoperative femoral fracture is a well recognized technical complication of cementless total hip arthroplasty (THA). The aim of this study was 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. An in vitro comparison of two methods of cerclage fixation was performed using steel wire (Protasul) versus multifilament Vitallium alloy cable. Ten fresh human femur specimens were studied. Longitudinal fractures were created on a material testing machine. The force to create a longitudinal fracture in the femur was 1915 N to 9288 N (median 6531 N). This force corresponds 3 to 15 times (median 11 times) the body weight. The femoral cortex was fractured in 5 cases ventrally, in 6 cases medially and in 1 case laterally. After monofile cerclage wire application, the force required to press the prosthesis 5 mm deeper into the medullary canal was 0.3-2.7 times body weight. After Vitallium alloy cable application in other specimens, the force was 1.3-2.7 times body weight. The difference was not statistically significant. After monofile cerclage wire application, a force of 1.8-8.1 times body weight was necessary to press the prosthesis 30 mm deeper into the medullary canal. After polyfile Vitallium alloy cable application in other specimens, the force was 7.7-12 times body weight. The difference was statistically significant (U-test, alpha < 0.025).