Accuracy of combined anteversion in image-free navigated total hip arthroplasty: stem-first or cup-first technique?

In total hip arthroplasty (THA), combined anteversion (CA) is used as a parameter for assessment of overall prosthetic alignment. The purpose of this study was to comparatively examine the CA value in patients who underwent primary THA using the image-free navigation system either with a cup-first or stem-first technique.

Eighty-three hips undergoing primary THA using the OrthoPilot® image-free navigation system (B. Braun-Aesculap, Tuttlingen, Germany) were included in this study. The patient population was divided into two groups depending on the procedure used: cup-first technique and stem-first technique. In the cup-first group, inclination and anteversion (AV) angles were targeted at 35-45° and 15-25°, respectively, while stem antetorsion (AT) was determined for each patient based on the amount of individual native femoral AT angle. In the stem-first group, the femur was prepared first with the target angle corresponding to the native femoral AT and the cup AV was decided considering the CA calculated with Widmer's formula (aiming at the optimal Widmer's CA of 37.3°).

Better consistency in Widmer's CA values was attained in the stem-first group as indicated by the smaller SD values. In the assessment of overall alignment, Widmer's CA values were within the satisfactory range (37 ± 5°) in 41.9 and 92.3 % of the subjects in the cup-first group and the stem-first group, respectively.

The stem-first technique with image-free navigated THA could effectively achieve accurate and consistent control of the CA value and thus is expected to improve the surgical outcome.