Use of a Digital Protractor and a Spirit Level to Determine the Intraoperative Anteversion of Femoral Component during Cemented Hip Hemiarthroplasty: a Prospective Clinical Trial.

Abstract

Femoral stem anteversion during hip arthroplasty is generally estimated by eye intraoperatively and has proven to be different from targeted values. This study aims to determine the accuracy of a novel technique using a digital protractor and a spirit level to improve surgeons' estimation of stem anteversion. A prospective non-randomized study was conducted among 93 patients with femoral neck fracture who underwent cemented hemiarthroplasty via posterolateral approach. In the control group (N=62), five experienced surgeons assessed stem anteversion related to the posterior femoral condylar plane using visual estimation with a target angle of 15°-25°. In the study group (N=31), another two surgeons assessed stem anteversion with the same target angle by placing a digital protractor on the femoral stem inserter handle while the assistant held the leg in the truly vertical position, verified by a spirit level that was attached to the shin with cable ties. Stem anteversion was measured blind, postoperatively, on 2D-CT and compared with the intraoperative results. The mean postoperative anteversion was 22.4° (-4.2° to 51.3°, SD 11.1°) in the control group and 23.0° (16.0° to 29.9°, SD 3.6°) in the study group (P=0.810). The study group had more stems positioned in 15°-25° anteversion (71.0% vs 32.3%, P=0.001) and the mean absolute value of surgeon error was -0.2° (-5.4° to 7.0°, SD 3.0°). Twenty-eight stems of the study group (90.3%) had an error within 5°. Surgeon overestimation >5° was found in 1 hip (3.2%) and underestimation >5° was found in 2 hips (6.4%). Using a digital protractor and a spirit level was reliable with high accuracy and precision to improve the intraoperative estimation of cemented stem anteversion.