Summary

The femoral and acetabular torsion cannot be predicted from x-rays, the anteversion of the acetabulum correlates with the acetabular inclination angle, the hip lateralization index and eventually the beta angle in dysplastic hips

Abstract

Background

To assess the degree of hip dysplasia two conventional radiographies of the pelvis (AP), including one axial view of the affected hip are performed to analyze the standard measures. However, little is known about the relation between the plain radiography and the acetabular torsion as well the other measurements of the rotational profile of the lower limb. Aim of this study was to investigate the impact of acetabular, femoral and rotational alignment between dysplastic and borderline dysplastic hips compared to conventional radiography.

Methods

Between 2017 and 2019, a retrospective trial was conducted including 56 borderline- and dysplastic hips at a mean age of 28.86 years (range from 18 to 46). Inclusion criteria consisted of symptomatic patients with hip dysplasia undergoing 2-dimensional radiography as well as computed tomography. On radiography the lateral center edge angle, acetabular arc, extrusion index, acetabular index and the sharp angle were measured, and the presence of crossover sign was noted. In computed tomography the full rotational profile of the lower limb was measured by a fellowship trained musculoskeletal radiologist.

Results

Significant correlations were observed in the overall analysis between the anteversion of the acetabulum and the hip lateralization index (mean 0.56, coefficient of regression (CoR) -32.35, p=0.011) as well as the acetabular inclination angle with a mean of 11.50 (CoR 0.544, p=0.018). Similar results were found in the subgroup of dysplastic hips with an acetabular inclination angle of 13.9 (p=0.013, CoR 0.74). For the borderline-dysplastic group no significances between the pelvis radiography and rotational CT were seen.

Conclusion

Although the femoral and acetabular torsion cannot be predicted from x-rays, the anteversion of the acetabulum correlates with the acetabular inclination angle, the hip lateralization index and eventually the beta angle in dysplastic hips. For borderline-dysplastic hips such results did not show up, which makes especially in these cases computed tomography indispensable for rotational analysis.