Anatomical Reconstruction of Femoral Torsion after Total Hip Arthroplasty: Comparing Short and Long-Stem Models

Objectives The optimal femoral stem fixation in primary total hip arthroplasty (THA) remains a challenge for surgeons and researchers. Literature has shown advantages for short-stem prostheses regarding bone stock and soft tissue preservation in comparison to straight-stem models. However, data on the reconstruction of femoral anteversion (FA) and consequently the center of rotation are rare. Our hypothesis was that curved short-stem fixation would allow for improved anatomical reconstruction of FA in comparison to a straight-stem design.

Methods We prospectively included 89 consecutive patients (38 female, 42.7 %) who underwent THA using a short-stem prosthesis (ANA NOVA Proxy^®, Implantec) at our institution (group A). A CT-scan from hip to ankle pre- and postoperatively was performed. Measurements were taken using MediCAD 3D (Hectec) software. As a control group (B), 41 patients who underwent THA using a straight stem prosthesis (Corail^®, DePuy Synthes) were included.

T-Test and Rank-Sum-Tests were used to test for group differences for parametric and non-parametric distribution. Regression analysis was used to detect differences in continuous variables.

Results and Conclusion Preoperative FA was 22.4°± 11.0°, the postoperative FA 23.4°± 10.1°. The relative difference was -0.8°±8°, and the absolute difference 6.4°±4.9°. Gender analysis revealed significant differences in preoperative FA between female (f) and male (m): 28.1°±11.2° vs. 18.4°±8.3°; p>0.001) as well as in the postoperative FA (f vs. m: 26.7°±23.5° vs. 21.0°±9.7°; p < 0.007) in group A. No such differences were found in group B when comparing the FA (f vs. m: 17.9°±9.9° vs. 15.7°±7.6°; p = 0.425). There was no difference regarding the absolute FA change from pre- to postoperative in group A (f vs. m: 7.6°±5.7° vs. 5.6°±4.0° p= 0.057). Further, there was no significant correlation between the change in pre- to postoperative FA and patient age (p = 0.657) or body-mass-index (p = 0.307) in this group. When comparing both groups, we found the postoperative FA to be larger in group A than in group B (mean 6.8°; 23,9°±10,1° vs. 16,6°±8,6°, p < 0,001).

When analyzing the short-stem cohort (group A), we found little differences regarding the pre- to postoperative change in the FA. We attribute this, as well as the differences in the gender analysis between the two groups, to a better femoral reconstruction when using a short-stem design rather than a straight-stem prosthesis. This is further underlined by the comparison of the postoperative FA between the groups.

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Artikel online veröffentlicht:
15. Oktober 2020