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Combined anteversion (CA) technique (stem-first procedure) has become generally accepted as an ideal means to achieve optimal CA value in THA. However, we hypothesized that CA technique for patients with various native femoral anteversions could pose a risk of anterior or posterior cup protrusion. In the present study, we examined whether it is possible to use the taper wedge stem to change the stem version to achieve optimal CA while avoiding cup protrusions with the cup-first procedure through minimally invasive (MIS) antero-lateral approach. Eighty-one patients underwent cup-first THA with a taper wedge stem. The acetabular cup was placed following the preoperative planning of the cup alignment to avoid anterior cup protrusions using CT-based navigation. Following the CA theory, anteversion of the taper wedge stem was changed to the target anteversion from the patient’s native femoral anteversion. The native femoral anteversion, the change in version angle of the stem, postoperative CA and the length of anterior cup protrusions were evaluated in postoperative CT measurements. The native femoral anteversion averaged 25.7° ± 8.9° (range 8°–45°). Cases with increased and decreased stem anteversion were observed in 42 hips (51.8%) and 33 hips (40.7%), respectively. The amount of increased and decreased version angles averaged 7.7° ± 4.8° (range 2°–21°) and 7.8° ± 5.1° (range 2°–20°), respectively. Postoperative CA values averaged 36.7° ± 3.4° (range 29.4°–44.2°) and anterior cup protrusion length averaged 2.0 mm ± 2.6 mm (0 ~ 8.8 mm) in axial view and 0.4 mm ± 1.0 mm (0 ~ 3.6 mm) in sagittal view. Anterior cup protrusion of more than 10 mm was not observed in any hips. This procedure can be considered as an option to achieve optimal CA anteversion while avoiding anterior cup protrusion in THA.

Combined anteversion (CA) technique (stem-first procedure) is generally accepted as the optimal technique to attain an appropriate CA value in total hip arthroplasty (THA). However, cup anteversion is strongly influenced by the native femoral anteversion. Accordingly, anterior protrusion of the cup in the acetabulum might occur. The purpose of the present study is to investigate the achievement of the optimal CA while avoiding anterior cup protrusion and examine the significance of our new CA technique with cup-first procedure in hybrid THA. Seventy-nine hybrid THAs with the cup-first procedure used a CT-based navigation system for cup positioning. In the preoperative planning, cup anteversion was aimed at approximately 20°. However, in actuality, sufficient cup coverage in the original acetabulum based on individual anatomy is given priority over cup placement based on CT-based planning to ensure adequate cup coverage. The target stem anteversion was determined following Widmer’s mathematical formula (37.3 = femoral stem anteversion × 0.7 + cup anteversion). Cemented stem was inserted according to the target stem anteversion angle. Regarding the assessment of overall alignment, the calculated Widmer’s CA values during surgery and postoperative CT evaluation were 34.1° ± 6.0° (range 20.7°–51.2°) and 35.1° ± 6.7° (range 21.6°–50.7°). There were 72 hips (91.1%) within 25°–50° of CA. Cup protrusion length averaged 2.0 mm ± 2.6 mm (0–8.8 mm) in the axial view and 0.4 mm ± 1.0 mm (0–3.6 mm) in the sagittal view. Cup protrusion length of more than 5 mm was indicated in 10 hips, and no hips observed more than 10 mm. Our new CA technique (cup-first procedure) with hybrid THA was able to achieve optimal CA value while avoiding anterior cup protrusion.