Rotational abnormalities in dysplastic hips and how to predict acetabular torsion

Abstract

Objectives The aim of this study was to investigate the degree to which conventional radiography can represent the acetabular and femoral rotational alignment profile between dysplastic and borderline-dysplastic hips. Methods A retrospective trial was conducted including 56 borderline-dysplastic and dysplastic hips at a mean age of 28.9 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 hip index, hip lateralization index, acetabular index angle, and the Sharp angle were measured, and the presence of a crossover sign was noted. In computed tomography, the full rotational profile of the lower limb was measured. 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 index 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 index angle of 13.9 (p = 0.013, CoR 0.74). For the borderline-dysplastic group, no significant correlations 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 index angle, the hip lateralization index, and eventually the beta angle in dysplastic hips. For borderline-dysplastic hips, such results did not show up, which strongly illustrates the need for computed tomography in these cases. Key Points • Much of the current literature focuses on rotational alignment especially with respect to the femur and tibia in healthy patients, although little is known about the acetabular, femoral, and tibial torsion in dysplastic hips. • This is the first study showing significant correlations between the anteversion of the acetabulum and the hip lateralization index as well as the acetabular inclination angle. Also, it is the first study to provide a mechanism for estimation of the torsion of the acetabulum with plain radiography in dysplastic hips. • In borderline-dysplastic hips, no significant correlation was found, which raises the question if a simple x-ray has enough validity to address the acetabular deformity with surgery.

The Impact of Hip Dysplasia on CAM Impingement

“…Left side: CE angle—between the Perkin line and the line between the center of the femoral head to the lateral edge of the acetabulum −18.8°; AI angle—between the Hilgenreiner’s line and a parallel line to the acetabular roof—12.3°; sharp angle—between the horizontal teardrop line and a line connecting the teardrop to the lateral acetabulum—43.9°; hip lateralization index—quotient between the horizontal distance of the lateral femoral head that is uncovered by the acetabulum divided by a horizontal width of the femoral head—0.54; anterior hip index—quotient of the femoral head that is covered by the acetabular roof and the width of the femoral head—73.9; CCD angle—between the axis of the femoral diaphysis and the axis of the femoral neck—137.4° and positive crossing over sign. Adopted from [ 14 , 15 ].…”

“…Figure 2. Preoperative measurements in a right-sided borderline dysplastic hip: CE angle-23.4 • ; AIA-4.9 • ; sharp angle-40.0 • ; hip lateralization-0.51; anterior hip index-82.8; CCD angle-121.0 • .Adopted from[14,15].…”