Femoral fracture risk in hip arthroplasty: smooth versus toothed instruments

Compaction of cancellous bone with smooth tamps in total hip arthroplasty has been shown to improve initial implant fixation. It is not known, however, whether this improved fixation occurs at the expense of an increased risk of intraoperative femoral fracture. The current authors explore this issue by comparing the risk of fracture in 10 pairs of femurs prepared with either smooth tamps or conventional toothed broaches. Using one pass for each size, smooth tamps were advanced incrementally into one femur of each pair and toothed broaches were advanced incrementally into the contralateral femur. A controlled impulse, representative of a typical impact during surgery, was applied to the instruments by a drop tower (mean starting force, 3017 N). When the instruments no longer advanced distally, the applied force was increased incrementally. Instrument sizes were increased until a femoral fracture was observed or the impact exceeded 8000 N without causing a femoral fracture. At preoperative templated size, significantly more femurs that had tamps had fractured (eight of 10), compared with femurs that had broaches (two of 10). Smooth tamps therefore increased the risk of intraoperative femoral fracture in vitro in this particular implant design developed for cemented fixation of the femoral component.