Hip resurfacing has recently become an alternative for total hip replacement, especially for younger and more active patients. Although early results are encouraging, there are reports of failure as a result of malpositioning of the femoral component. To help overcome this problem we developed a CT-guided computer-assisted system for the planning and guidance of the femoral component during hip resurfacing. 3D isosurface models were generated from a CT scan of the pelvis and proximal femur. By superimposing virtual prosthetic components, the surgeon preoperatively determined the size, position and orientation of the femoral component. Intraoperatively, an optoelectronic navigation system was used for realtime CT-guidance of the insertion of the alignment pin for the femoral component. In a laboratory study, the precision of the intraoperative guidance system was investigated. One experienced and one inexperienced surgeon performed one posterior and one anteriolateral approach on 10 different plastic bone models. After each procedure, the alignment-pin orientation was compared to the planned orientation. In a preliminary clinical study, 27 patients underwent the computer-assisted method and 13 patients were operated on using conventional technique. Both posterior and anteriolateral surgical approaches were used. Pre-operative and postoperative neck-shaft angles were compared using Student’s t-test. In the laboratory study, the mean deviations between planned and navigated alignment-pin orientation was 0.65° (StDev 0.9°) for the experienced surgeon, and 0.13° (StDev 0.7°) for the inexperienced surgeon. The mean deviation of anteversion angles were measured as 0.31° (StDev 0.8°) for the experienced surgeon and 0.01° (StDev 0.9°) for the inexperienced surgeon. In the clinical study, we measured the neck-shaft angle in the computer-assisted group to be an average of 133° preoperatively and 134° postoperatively (p=0.16), and in the conventional group to be an average of 136° pre-operatively and 135° postoperatively (p=0.79). There were no significant differences between pre-operative and post-operative measurements between the groups. However, there was a significantly lower standard deviation in the postoperative computer-assisted group: it was 6.6°, compared to 13.3° in the conventional group (Levene’s test for equality of variances, p=0.004). We conclude, based on our results, that a CT-guided system can help to prevent femoral misalignment during a hip resurfacing by increasing the intraoperative precision.
