Abstract
Introduction
Malpositioning of the acetabular cup during total hip arthroplasty increases the risk of dislocation, edge loading, squeaking and can be responsible for early wear and loosening. We hypothesized that the use of three-dimensional visualization tools showing during surgery the planned cup position relatively to the acetabular edge would increase the accuracy of cup orientation. The purpose of this study was to compare 3D planning-assisted with freehand insertion of the acetabular cup.
Methods
A randomized, controlled, prospective study of two groups of twenty eight patients each was performed. In the first group, cup positioning was guided by 3D views of the cup within the acetabulum based on a three-dimensional preoperative planning (Figure 1). In the control group, the cup was placed freehand. All of the patients were operated on by the same surgeon through a direct anterior approach in supine position. Cup anteversion and abduction angles were measured on three-dimensional computed tomography reconstructions for each patient by an independent observer. We analyzed the accuracy of both methods. The main evaluation criterion was the percentage of outliers according to the Lewinneck safe zone.
Results
There was no difference in surgery time between the two groups. The cup anteversion angle was restored with a higher accuracy in the 3D-assisted group (−2.7 ± 5.4°) comparatively to the freehand-placement group (6.6 ± 9.5°, p<0.0008) (Figure 2). The percentage of outliers was twice lower in the 3D guided group (21%, 6 patients) comparatively to the control group (46%, thirteen of twenty eight p=0.04). According to the Callanan safe zone, the percentage of outliers was also lower in the 3D guided group (32%, versus 75%, p = 0.001) (Figure 3). The surgeon tends to position the cup with a higher anteversion than the native acetabulum anteversion.
Conclusions
The use of a 3D preoperative planning can improve cup positioning in total hip arthroplasty by increasing the accuracy of the anteversion restoration and reducing the percentage of outliers. When using a direct anterior approach in supine position, the surgeon may tend intuitively to implant the cup with a higher anteversion value comparatively to the native acetabulum anteversion because of the postero-caudal overcoverage of the cup that gives a false impression of cup retroversion.
