ALIGNED FEMORAL RASPING IN CEMENTLESS TOTAL HIP > ARTHROPLASTUSING GUIDE INSIDE FEMORAL CANAL

In the cementless total hip arthroplasty, the position of the stem is pretty much determined by broach and rasping with which the is required for two reasons: one is to align the stem with the femur at the desired position and the orientation. The other is to achieve the conformity between the stem and the prepared proximal cavity surface in the femur. The robotic hip surgery can be a solution for the accurate of femoral canal shaping, but recent reports about the clinical follow-up study of the robotic hip surgery indicated frequent dislocation mainly due to the excessive soft tissue damage during robotic operation. In this paper, a guide being inserted into the femoral canal is proposed to restrict the undesired motion of the rasp inside the femur without extra incision. A set of canal guide and custom rasp for the selected stem(versys fibermetal midcoat, zimmer co.)were developed and tested with 4 synthetic femurs (model 1130, Sawbones co.). After rasping, a plastic copy of the stem was inserted into the femur and sliced at 5 mm thickness. From obtained cross sections, percentages of the gap larger than 0.3mm between the stem and the bone was measured. 6\_C\_Results: In average, 79% of bone-implant interface was close contact. Valgus/varus deviations of the stem were 0.40±0.45 degree, which means the angle of axis of straight reamer and axis of final cut. In average, 79% of bone-implant interface was close contact. Valgus/varus deviations of the stem were 0.40±0.45 degree, which means the angle of axis of straight reamer and axis of final cut. The conformity of femoral canal with the femoral stem in this approach was higher than the conventional hip surgery and comparable to those in the robotic surgery. The alignment of the stem within the femur is also as good as those in the robotic surgery(0.34±0.67 approach does require neither expensive system nor CT scan. Also this approach can be executed swiftly without extra time and unnecessary large incision compared with the robotic surgery.