For hip resurfacing arthroplasty, precise planning and implantation of the components is necessary for long-term success. Earlier studies have shown that a computer-assisted technique can achieve higher accuracy than conventional technique. However, many of the proposed computer systems add additional complexity, time and cost to the surgery. This study investigated the use of rapid prototyping as an accurate, fast and cost-effective solution for computer-aided hip resurfacing. From a CT scan of each patient, a 3-dimensional computer model of the proximal femur was produced and the drilling trajectory for the central pin of the stem was planned. To transfer this plan to the patient, surface-matched plastic drilling templates were created using a rapid prototyping machine. Depending on the surgical approach, these templates contained a mirror-image of parts of the anterior or posterior femoral head and neck. These mirror-image templates helped to exactly position the drilling guide on the bone during surgery, which ensures a precise transformation of the preoperative plan into the surgical field. To test the accuracy and reproducibility of this system, we created plastic models of three cadaver femurs using the rapid prototyping machine. For each of these femurs one anterior and one posterior drilling template were generated. Each template was applied three times to the femur model and the direction of the drilling target was recorded and axis deviations measured. The average deviation between the planned and the template-guided drill direction was 1.3° for the anterior approach and 1.2° for the posterior approach. The reproducibility for the drilling axis was measured for the anterior approach as 0.4° and posterior 0.3°. In comparison to previous published results for computer-assisted hip resurfacing, our results show similar or better accuracy. Further in-vitro and in-vivo experiments will be performed to obtain statistically significant accuracy measurements and intraoperative feasibility tests. Our early results show great potential for this technique for accurate and in-expensive guidance for hip resurfacing.
