Precision and bias of imageless computer navigation and surgeon estimates for acetabular component position.

Computer navigation has the potential to permit accurate placement of components. We first hypothesized acetabular inclination and anteversion using navigation would be within 5 degrees of postoperative computed tomography scans, then secondly, computer precision would be better than that of surgeons. In the first phase, we obtained postoperative CT scans in 30 hips to ascertain the computer navigation values for inclination and anteversion of the cup. In the second phase, in 99 patients with 101 hips, we determined the surgeon's precision by comparing surgeons' blind estimates for trial cup position with computer navigation values. The navigation precision for inclination was 4.4 degrees with a bias of 0.03 degrees and for anteversion was 4.1 degrees with a bias of 0.73 degrees. The experienced surgeons' precision was 11.5 degrees for inclination and 12.3 degrees for anteversion, whereas the less experienced surgeons' precision was 13.1 degrees for inclination and 13.9 degrees for anteversion. The data supported the first hypothesis as computer navigation had a bias for inclination and anteversion of less than 1 degrees with precision less than 5 degrees. The precision of computer navigation was better than that of surgeons. This imageless computer navigation system allows more accurate acetabular component placement.