Biomechanical stability of four-part intertrochanteric fractures in cadaveric femurs fixed with a sliding screw-plate.

Three factors affecting the stability of four-part intertrochanteric fractures were considered; the type of reduction, the quality of bone as assessed by the Singh Index, and the position of the sliding screw within the head fragment. The stability of two different reductions of four-part intertrochanteric fractures created in paired cadaveric femurs was tested after fixation with sliding screw-plates. Cyclic loading over the range 1-6 times body weight was used to simulate physiological forces. The same loading regimen was applied to femurs with deliberately misplaced implants. Bone quality did not affect the incidence of failure. The type of reduction did not affect the incidence of failure, although it affected the mode of failure. Misplacing the implant greatly impaired the stability of the fracture. Thus, to minimize the risk of disruption of the reduced fracture every attempt must be made to ensure that the tip of the nail or plate lies between 5 and 12 mm from the subchondral bone of the femoral head and the shaft of the device in the central third of the neck on both anteroposterior and mediolateral radiographs.