The dimensional accuracy of preparation of femoral cavity in cementless total hip arthroplasty.

OBJECTIVE To observe the accuracy of femoral preparation and the position of the cementless prosthesis in femoral cavity, and to compare the results between the computer-assisted surgical group (CASPAR) and the conventional group. METHODS Ten femoral components were implanted either manually or by CASPAR in cadaver femurs. The specimens were cut to 3 mm thick slices. Microradiograms of every slice were sent to a computer for analysis with special software (IDL). The gaps and the medullary cavities between component and bone, the direct bone contact area of the implant surface, the gap width and the percentage of gap and bone contact area were measured in every slice. RESULTS In the proximal implant coated with HA of the CASPAR group, the average percentage of bone contact reached 93.2% (ranging from 87.6% to 99.7%); the average gap percentage was 2.9% (ranging from 0.3% to 7.8%); the maximum gap width was 0.81 mm and the average gap width was only 0.20 mm. While in the conventional group, the average percentage of bone contact reached 60.1% (ranging from 49.2% to 70.4%); the average gap percentage was 32.8% (ranging from 25.1% to 39.9%); the maximum gap width was 2.97 mm and the average gap width was only 0.77 mm. The average gap around the implant in the CASPAR group was only 9% of that in the manual group; the maximum and average gap widths were only about 26% of those in the manual group. On the other hand, the CASPAR group showed 33% tighter bone contact than the manual group. CONCLUSION With the use of robotics-assisted system, significant progress can be achieved for femoral preparation in total hip arthroplasty.