A simple angle-measuring instrument for measuring cemented stem anteversion during total hip arthroplasty

Background During total hip arthroplasty (THA), the accurate placement of the femoral components is an important determinant of the success of the procedure. This study assessed the accuracy of cemented stem placement using a new angle-measuring instrument. The primary objective was to investigate the accuracy of the intraoperative measurements of cemented stem anteversion obtained using the angle-measuring instrument. Our secondary objective was to evaluate the accuracy of stem positioning performed using the angle-measuring instrument. Methods We compared the intraoperative stem anteversion measurements obtained using the angle-measuring instrument with postoperative stem anteversion measurements obtained using computed tomography in 149 hips (measurement accuracy). We also compared the target angle and postoperative stem anteversion in 105 hips (implantation accuracy). Results The mean amount of intraoperative stem anteversion was 37.9 degrees +/- 10.1 degrees, and the mean amount of postoperative stem anteversion was 37.0 degrees +/- 10.4 degrees. The mean measurement accuracy was 0.9 degrees +/- 6.1 degrees, and the absolute measurement accuracy was 4.9 degrees +/- 3.7 degrees. The correlation coefficient for the relationship between the intraoperative and postoperative stem anteversion measurements was 0.824 (p = 0.000). The mean amount of target angle was 37.4 degrees +/- 7.6 degrees, and the mean amount of postoperative stem anteversion was 35.9 degrees +/- 9.1 degrees. The mean implantation accuracy was 1.4 degrees +/- 5.6 degrees, and the mean absolute implantation accuracy was 4.3 degrees +/- 3.6 degrees. The correlation coefficient for the relationship between the target angle and postoperative stem anteversion was 0.795 (p = 0.000). Conclusions The angle-measuring instrument measured intraoperative stem anteversion accurately, and cemented stem was implanted accurately during THA with the angle-measuring instrument.