Higher femoral anteversion restoration accuracy after total hip arthroplasty with a proximally fixed anatomic stem than with a generic straight double-tapered stem.

Abstract

Femoral antetorsion in uncemented hip replacement hardly can be modified and the restoration of the anatomic anteversion might be difficult with standard stems. We compared femoral anteversion restoration of a generic straight stem with a proximally fixed anatomic stem that included a dual sagittal curvature and a proximal torsion. It was hypothesised that the restoration of the anteversion was more accurate with the anatomic stem. In this comparative study data were collected prospectively of 80 consecutive patients with total hip arthroplasty for primary osteoarthritis. In the first 40 patients (Group I) a cementless proximally fixed anatomic stem with 15° antetorsion of the shaft and a dual sagittal curvature was used. Its design was based on a database of 3D CT images of 600 hips. For comparison a cementless generic straight double-tapered stem was implanted in the next 40 patients (Group II). All operations were performed by one experienced surgeon. All patients had a preoperative 3D planning. A low-dose CT scan was performed at 3 months postoperatively to determine the postoperative stem anteversion. The demographics were similar in both groups. In group I the mean postoperative femoral anteversion was similar to the preoperative one (22.1° ± 10.2° vs. 20.4° ± 9°; p = 0.2). In Group II, the mean postoperative femoral anteversion was lower (12.9° ± 10.8°, vs. 18.3° ± 12°; p = 0.02). Uncemented standard femoral stems tend to reduce femoral anteversion. The used anatomic stem restored femoral anteversion better. The clinical impact of this finding has to be proven.