Implant positioning is one of the critical factors influencing postoperative outcomes in total hip arthroplasty (THA). Several studies have reported that the postoperative antetorsion (AT) measurement for the femoral stem inserted without navigation showed wide variability. The current authors developed a simple instrument, the Gravity-guide (G-guide), for intraoperative assessment of stem AT and adjustment. They evaluated the effectiveness of the G-guide with postoperative computed tomography (CT) examination. Ninety patients (96 hips) who underwent primary THA using the G-guide for stem adjustment were evaluated. The G-guide consists of 2 parts: one attached to the lower leg and the other attached to the handle of the rasp. The G-guide was used to evaluate the AT at the time of inserting the final rasp. In addition, the AT value in the G-guide evaluation system required correction by the angle obtained in the preoperative epicondylar view. Intraoperative stem AT was defined as the sum of the intraoperative G-guide value and the correction angle. Postoperative AT was evaluated by CT examination. The discrepancy between the intra- and postoperative measurements was 4.6°±4.1°. Acceptable accuracy with discrepancy of less than 5° and 10° was achieved in 66 (69%) hips and 85 (89%) hips, respectively. The use of the G-guide could effectively reduce the variability of stem anteversion compared with manual adjustment. This study proved the effectiveness of the newly developed G-guide system in intraoperative stem AT adjustment.
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