Measures of anterior hip coverage in adult patients with hip dysplasia / 中华骨科杂志

ABSTRACT

Hip dysplasia occurs when the acetabulum does not cover the femoral head sufficiently, causing hip instability and pain. Acetabular coverage of the femoral head is an important index to evaluate the stability of the hip joint. Further, anterior hip coverage is as important as lateral coverage in the stability of the hip joint. However, the measurements of anterior hip coverage received less attention and enjoyed less consensus than those of lateral hip coverage. The existing measurements of the adult hip joint can be divided into 2 categories, namely three-dimensional (3D) measurements and two-dimensional (2D) measurements. 2D measurements include the anterior central-edge (ACE) angle and the anterior acetabular head index on false-profile radiographs, the ACE angle on sagittal CT radiographs, and the anterior wall index, the rule of thirds, the crossover sign and the crossover index on standing pelvic anteroposterior radiographs. Among the above indexes, the ACE angle and anterior acetabular head index can be directly measured on false-profile radiographs, which can reproduce the weight-bearing function of the standing hip joint. Currently, these indexes are widely used in the clinical practice to determine the stability of hip joints. Some evidence indicated correlation of these indexes with satisfied clinical outcomes. The ACE angle on CT sagittal radiographs acquired from CT data reproduces the patients' status in the supine position. It is used for determining the potential femoroacetabular impingement after hip correction. The anterior wall index, rule of thirds, crossover sign and crossover index are obtained on standing pelvic radiographs, which can reproduce the weight-bearing status of hip joints and reduce the need for a false-profile radiograph. The surgeon can reach a preliminary judgment from these measurements in a short time. However, due to some potential influence factors, the accuracies of these 2D measurement indexes are limited. Further, their clinical relevance according to published studies is not consistent. 3D measurements include real 3D measurement based on CT and the simulated 3D (2.5D) measurement based on statistical models. The details of acetabular morphology are most accurately described in 3D measurements. They are used to determine the influence of acetabular osteotomy on the range of motion and to predict the risk of postoperative iatrogenic femoroacetabular impingement. Although 2.5D measurement based on statistical models is more accurate than that based on 2D measurements, it is still based on the anteroposterior radiographs of the pelvis. Therefore, the drawback caused by using anteroposterior radiographs cannot be eliminated completely. In summary, the ACE angle on false-profile radiographs is the most commonly method in clinical practice.