New combined anteversion technique in hybrid THA: cup-first procedure with CT-based navigation.
PURPOSE
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.


METHODS
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.


RESULTS
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.


CONCLUSION
Our new CA technique (cup-first procedure) with hybrid THA was able to achieve optimal CA value while avoiding anterior cup protrusion.
['Masumoto|Yoshinobu|Y|', 'Fukunishi|Shigeo|S|', 'Fukui|Tomokazu|T|', 'Yoshiya|Shinichi|S|', 'Nishio|Shoji|S|', 'Fujihara|Yuki|Y|', 'Okahisa|Shohei|S|', 'Okada|Taishi|T|', 'Kanto|Makoto|M|', 'Goshi|Ariha|A|', 'Morio|Futoshi|F|', 'Takeda|Yu|Y|']
D000077:Acetabulum D000328:Adult D000368:Aged D000369:Aged, 80 and over D019644:Arthroplasty, Replacement, Hip D005260:Female D006622:Hip Prosthesis D006801:Humans D008297:Male D008875:Middle Aged D015641:Radiography, Interventional D014057:Tomography, X-Ray Computed
Combined anteversion Hybrid THA Cup protrusion CT navigation