In total hip arthroplasty (THA), the concept of combined anteversion is accepted as one of best indicators of prosthetic joint stability. Technical parameters may influence the stem and cup anteversion. We therefore investigated if stem anteversion could be influenced by surgical approaches in cementless THA using a tapered wedge stem with stem-first technique.

We postulated that the type of approach, posterolateral (PLA) or anterolateral approach (ALA), would influence stem anteversion in dysplastic hip patients. We asked (1) whether stem anteversion was higher in the PLA group and (2) how postoperative stem anteversion was correlated to preoperative femoral anteversion in each group.

We retrospectively compared two groups of hips that underwent THA using a tapered wedge stem with the posterolateral (PLA group; 154 hips) or anterolateral (ALA group; 81 hips) approaches. Computed tomography was utilized to measure femoral neck and stem anteversion. To investigate related factors that affect stem anteversion, a stepwise regression analysis was performed.

The stem anteversion in the PLA and ALA groups was 43.7°±9.8° and 34.0°±12.3°, respectively (p<0.01). The stepwise selection process resulted in a model involving femoral neck anteversion and surgical approach (p<0.01). The stem anteversion of the ALA group (r=0.75, p<0.01) was better correlated to femoral neck anteversion than that of the PLA group (r=0.52, p<0.01).

The stem implantation through the ALA is thought to be more restricted than that through the PLA due to the difference of difficulty in femoral exposure. Tapered wedge stems, which are relatively thin and flat, have a high degree of freedom in the femoral canal. Consequently, in cementless THA using a tapered wedge stem, the surgical approaches affected stem anteversion differently. Stem anteversion was more anatomically restored to femoral neck anteversion through the ALA than through the PLA.

III, retrospective case-control study.