抄録
Objective: The purpose of this study was to evaluate the accuracy of placement of implants for total hip arthroplasty (THA), which were measured by computed tomography (CT) with an ultrasound-based navigation (USBN) system.
Methods: CT evaluations were performed in 44 patients who underwent THA with USBN. The mean age at surgery was 67 years. All surgeries were performed in the supine position with the direct anterior approach. The OrthoPilot® imageless navigation system was used intraoperatively. Evaluation of the cup inclination angle (CIA), cup anteversion angle (CAA), and stem antetorsion angle (SAA) was carried out. Instead of SAA, the navigation system indicates the rasp antetorsion angle during surgery. The accuracy of the imageless navigation system was evaluated by comparison of the navigation values obtained intraoperatively with the CT measured values.
Results: The mean CIA was 39.6±4.1° (mean±sd) and the CAA was 18.5±6.1° in anterior pelvic plane with CT evaluation. USBN showed 39.0±3.2° in CIA and 18.8±5.9° in CAA intraoperatively. The mean absolute difference in CIA and CAA between navigation and CT was 2.4±2.1° and 2.2±2.7°, respectively. USBN showed a similar accuracy of placement of the cup compared to the reported accuracy with CT-based navigation. The rasp antetorsion angle was 28.6±10.0° and the mean SAA was 28.8±9.3°. A strong correlation was found between the rasp antetorsion angle and SAA (r2=0.737).
Conclusion: CT-free navigation has a definite advantage because of its easy method of pelvic and femoral registration, and no need for special preparation for surgery compared with CT or image-based navigation. USBN is a useful tool for performing accurate surgery for THA.
