New combined anteversion technique in hybrid THA: cup-first procedure with CT-based navigation
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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.
KeywordsCombined anteversion Hybrid THA CT navigation Cup protrusion
This study was approved by our Institutional Review Board (Nishinomiya Kaisei Hospital). The authors thank Mr. Devin Casadey and Miss. Rebecca Imaizumi for their assistance in editing the English manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
There is no funding source.
This article does not contain any studies with human participants or animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
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