Portable imageless navigation system and surgeon's estimate for accurate evaluation of acetabular cup orientation during total hip arthroplasty in supine position.

Abstract

This prospective study aimed to clarify whether this novel device can evaluate the cup orientation during total hip arthroplasty (THA) more closely to that measured in postoperative computed tomography (CT) compared to the surgeon's estimate using a manual goniometer. We prospectively performed 30 cementless THAs via the anterolateral approach in supine position between October 2018 and July 2019, wherein cup orientation was evaluated by both a portable imageless navigation system (HipAlign) and a manual goniometer during surgeries. Primary outcome was the absolute estimate error [the absolute value of the difference between cup angles measured by postoperative CT and those measured by HipAlign (group H) or surgeon's estimate using the manual goniometer (group S) during surgery]. The number of outliers of the absolute estimate error (> 10°) in each group was also estimated. The absolute estimate error of cup inclination in groups H and S was 3.3° ± 2.7° and 3.0° ± 2.5°, respectively (p = 0.51), whereas that of cup anteversion was 3.8° ± 3.4° and 6.0° ± 3.7°, respectively (p = 0.0008). The number of outliers of the estimate error in groups H and S was one case (3.3%) and six cases (20.0%), respectively (p = 0.04). In all six outlier cases, surgeons underestimated cup anteversion during surgeries. This portable imageless navigation system was a useful method, especially for avoiding incorrect cup anteversion. Underestimation of cup anteversion during THA in the supine position with the conventional alignment assisting device should be given attention.