Combined anteversion of the total hip arthroplasty implanted with image-free cup navigation and without stem navigation

In total hip arthroplasty (THA), combined anteversion (CA), the sum of cup anteversion (AV) and stem antetorsion (AT) are used as parameters to assess the appropriateness of overall prosthetic alignment. In this study, we evaluated the CA value based on the post-operative computed tomography (CT) measurements in our patient population who underwent THA using the OrthoPilotTM image-free navigation system (B/BRAUN-Aesculap, Tuttlingen, Germany). During surgery, cup alignment was adjusted with the use of the navigation system while the positioning of the femoral stem was arbitrarily adjusted by the surgeon. Seventy-nine THAs were included in the study. Post-operative CT assessment for the prosthetic alignment showed the average cup inclination and AV values to be 40.5 degrees +/- 4.1 degrees and 20.6 degrees +/- 4.6 degrees, respectively, demonstrating the effectiveness of the navigation system by small values of standard deviation. By contrast, the AT value measured for the stem showed wide variability (mean 23.6 degrees +/- 11.2 degrees). Consequently, the resulting CA was also inconsistent (mean 44.4 degrees +/- 11.2 degrees) and only 61 of the 79 THAs (77.2%) were defined as satisfactory.