Accuracy of intraoperative estimation of femoral stem anteversion in cementless total hip arthroplasty by using a digital protractor and a spirit level

BackgroundThe femoral component anteversion during surgery is traditionally assessed by a visual assessment of the surgeon and has proven to be imprecise. We sought to determine the accuracy of a digital protractor and a spirit level to measure the stem anteversion during cementless THA.MethodsA prospective study was conducted among 107 patients (114 hips) who underwent primary cementless THA via posterolateral approach. A pipe with a spirit level was attached to the tibial tubercle and intermalleolar midpoint. While the leg was held perpendicularly to the floor, stem anteversion was estimated by 3 methods: method A by visual assessment; method B by a digital protractor alone; and method C by a digital protractor combined with a spirit level. The angles were compared with the true anteversion measured by postoperative CT scan.ResultsThe average anteversion by method C (22.8 degrees 6.9 degrees, range -2 degrees to 40 degrees) was significantly lower than method A (24.6 degrees 5.2 degrees, range 0 degrees to 30 degrees) (p=0.033), but not different from the true anteversion (22.1 degrees +/- 8.2 degrees, range -5.4 degrees to 43.1 degrees) (p=0.445). There were no significant differences between method B (23.2 degrees +/- 8.2 degrees, range -4 degrees to 45 degrees) and method A, C or the true anteversion. The mean deviation of the intraoperative estimation from the true anteversion was 0.8 degrees +/- 3.7 degrees (range -7.1 degrees to 8.0 degrees) by method C; 1.2 degrees +/- 5.1 degrees (range -8.8 degrees to 14.3 degrees) by method B; and 2.5 degrees +/- 7.4 degrees (range -19.0 degrees to 16.0 degrees) by method A. Estimation error within 5 degrees was found in 107 hips (93.9%) with method C; 86 hips (75.4%) with method B; and 59 hips (51.8%) with method A.ConclusionAccurate estimation of stem anteversion during cementless THA can be determined intraoperatively by the use of a digital protractor and a spirit level.Trial registrationThai Clinical Trials Registry (TCTR 20180326003). Registered on 20 March 2018. Retrospectively registered.