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 hasproven to be different from targeted values. This study aims to determine the accuracy of a novel technique using adigital 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 whounderwent cemented hemiarthroplasty via posterolateral approach. In the control group (N=62), five experiencedsurgeons assessed stem anteversion related to the posterior femoral condylar plane using visual estimation with atarget angle of 15°-25°. In the study group (N=31), another two surgeons assessed stem anteversion with the sametarget angle by placing a digital protractor on the femoral stem inserter handle while the assistant held the leg in the trulyvertical position, verified by a spirit level that was attached to the shin with cable ties. Stem anteversion was measuredblind, 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 (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°). Twentyeightstems 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 theintraoperative estimation of cemented stem anteversion.Level of evidence: II