Stem torsion in total hip replacement

Methods 60 patients requiring total hip arthroplasty were prospectively enrolled in this study. Minimally invasive THR was performed (anterior approach) in a lateral decubitus position and each patient underwent a postoperative CT examination. The position of the stem was evaluated by an independent external institution. Results Stem torsion ranged from -19 degrees retrotorsion to 33 degrees antetorsion. Normal antetorsion (i.e 10-15 degrees according to Tonnis) was present in 5 of 60 patients, so the prevalence of abnormal stem antetorsion was 92% (95% CI: 82-97). We found a stem antetorsion outside the range of 0-25 degrees in 21 of 60 hips. Women had a higher mean stem antetorsion (8.0 degrees (SD 11)) than men (1.5 degrees (SD 10)). Interpretation Postoperative stem antetorsion shows a high variability and is gender-related. We suggest precise assessment of stem antetorsion intraoperatively by means of computer navigation, preparing the femur first. In abnormal stem antetorsion, the cup position can be adjusted using a combined anteversion concept; alternatively, modular femoral components or stems with retroverted or anteverted necks (retrostem) could be used.