Abstract
In recent years, there has been a controversial discussion about whether borderline dysplastic hips should be treated with an arthroscopic procedure or rather with an acetabular reorientation. New research suggests that a classification into stable and unstable hips may be helpful. The aim of the study was to validate (1) the intra- and interobserver reliability of a newly defined radiographic parameter named the Gothic Arch Angle, (2) the association between the GAA and previously existing measurements used to define severity of acetabular dysplasia, and (3) the correlation between radiographic measurements of acetabular dysplasia with MRI findings previously suggestive of hip instability. We defined and validated the GAA in 10 standardized radiographs of asymptomatic hips by two observers and calculated intra- and interobserver coefficients at two individual dates. Subsequently, a consecutive series of 100 patients with dysplastic hips (LCEA < 25°, Toennis grade ≤ 1) were evaluated for signs of instability on anteroposterior (a.p.) pelvic radiographs and direct MR arthrography and were divided in two groups: stable and unstable. In these patients the LCEA, the AI, the FEAR index and the GAA were radiographically evaluated. Correlation analyses and a logistic regression analysis was performed to identify the predictive value of instability for each radiographic parameter. Cutoff probabilities analysis was performed using standard receiver operating characteristic (ROC) curves to rate the predictive efficiency value of the GAA. The GAA showed excellent inter- and intraobserver reliability. A correlation was found between GAA and FEAR index. A logistic regression analysis showed that LCEA, FEAR index and GAA are distinct predictors of instability in hip dysplasia. The GAA showed the largest area under the curve (AUC 0.96), indicating it to be the best predictor of instability with an optimal cutoff value of 90° (sensitivity, 0.95; specificity, 0.93). The GAA is a new available indicator for instability and is thus suggested to be used as a future radiographic parameter for the stability of dysplastic hips. Further studies are needed to understand how this parameter might additionally predict clinical outcome in the treatment of hip dysplasia.Level of evidence: Level III, diagnostic study.
Highlights
Developmental dysplasia of the hip (DDH) is defined as osseous deficiency of the acetabulum with abnormal coverage of the femoral head which may lead to an overload and joint instability with subsequent damage of the acetabular cartilage or labrum[1,2,3,4]
The tip off the gothic arch lies on the line of application of the compressive force, which is perpendicular to the weight-bearing surface (WBS) and passes through the center of rotation
We assume that the concept of the gothic arch and the Femoro-Epiphyseal Acetabular Roof (FEAR) Index should be combined in order to achieve a higher predictive capacity with regard to hip stability
Summary
Developmental dysplasia of the hip (DDH) is defined as osseous deficiency of the acetabulum with abnormal coverage of the femoral head which may lead to an overload and joint instability with subsequent damage of the acetabular cartilage or labrum[1,2,3,4]. According to Pauwels and Maquet, the epiphyseal plate orientates perpendicular to the joint reaction force in accordance with the Hueter–Volkman principle[15,17]. In dysplastic hips the tip moves medially and the WBS shifts craniolaterally steeper This in turn leads to a force directed craniolaterally, which results in increased tension on the hip capsule and to craniolateral displacement of the femoral head. We assume that the concept of the gothic arch and the FEAR Index should be combined in order to achieve a higher predictive capacity with regard to hip stability. We have revisited Bombelli’s concept, amended it by the analysis of the femoral epiphyseal growth plate and defined a new measurement parameter for instability of the hip, called the Gothic Arch Angle (GAA). The aims of this study were (1) to validate the intra- and interobserver reliability of a newly defined radiographic parameter named the Gothic Arch Angle, (2) to validate the association between the GAA and previously existing measurements used to define severity of acetabular dysplasia, and (3) to validate the correlation between radiographic measurements of acetabular dysplasia with MRI findings previously suggestive of hip instability
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