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.

Background: 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.

Methods: 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.

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 (). The study group had more stems positioned in 15°-25° anteversion (71.0% 32.3%, ) 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%).

Conclusion: Using a digital protractor and a spirit level was reliable with high accuracy and precision to improve the intraoperative estimation of cemented stem anteversion.