How Are Dysplastic Hips Different? A Three-dimensional CT Study

The etiology of osteoarthritis of the hip has long been considered secondary (eg, to congenital or developmental deformities) or primary (presuming some underlying abnormality of articular cartilage). Recent information supports a hypothesis that so-called primary osteoarthritis is also secondary to subtle developmental abnormalities and the mechanism in these cases is femoroacetabular impingement rather than excessive contact stress. The most frequent location for femoroacetabular impingement is the anterosuperior rim area and the most critical motion is internal rotation of the hip in 90 degrees flexion. Two types of femoroacetabular impingement have been identified. Cam-type femoroacetabular impingement, more prevalent in young male patients, is caused by an offset pathomorphology between head and neck and produces an outside-in delamination of the acetabulum. Pincer-type femoroacetabular impingement, more prevalent in middle-aged women, is produced by a more linear impact between a local (retroversion of the acetabulum) or general overcoverage (coxa profunda/protrusio) of the acetabulum. The damage pattern is more restricted to the rim and the process of joint degeneration is slower. Most hips, however, show a mixed femoroacetabular impingement pattern with cam predominance. Surgical attempts to restore normal anatomy to avoid femoroacetabular impingement should be performed in the early stage before major cartilage damage is present. Level V, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

A new periacetabular osteotomy of the pelvis has been used for the treatment of residual hip dysplasias in adolescents and adults. The identification of the joint capsule is performed through a Smith-Petersen approach, which also permits all osteotomies to be performed about the acetabulum. This osteotomy does not change the diameter of the true pelvis, but allows an extensive acetabular reorientation including medial and lateral displacement. Preparations and injections of the vessels of the hip joint on cadavers have shown that the osteotomized fragment perfusion after correction is sufficient. Because the posterior pillar stays mechanically intact the acetabular fragment can be stabilized sufficiently using two screws. This stability allows patients to partially bear weight after osteotomy without immobilization. Since 1984, 75 periacetabular osteotomies of the hip have been performed. The corrections are 31 degrees for the vertical center-edge (VCE) angle of Wiberg and 26 degrees for the corresponding angle of Lequesne and de Seze in the sagittal plane. Complications have included two intraarticular osteotomies, a femoral nerve palsy that resolved, one nonunion, and ectopic bone formation in four patients prior to the prophylactic use of indomethacin. Thirteen patients required screw removal. There was no evidence of vascular impairment of the osteotomized fragment.

More than 90% of patients with so-called primary or idiopathic osteoarthritis of the hips in whom sufficient data were available to make an assessment of the normality of the hip joint at the cessation of growth clearly showed demonstrable abnormalities in the hip joint. The most common are mild acetabular dysplasia and/or pistol grip deformity. This latter deformity is associated with mild slipped capital femoral epiphysis (recognized or unrecognized at the time), Legg-Perthes' disease (recognized or unrecognized at the time), multiple epiphyseal dysplasia, spondyloepiphyseal dysplasia, and/or the presence of an intraacetabular labrum, as well as, in certain instances, acetabular dysplasia. When these abnormalities are taken in conjunction with the detection of other metabolic abnormalities that can lead to osteoarthritis of the hip and which may not be recognized readily, such as hemochromatosis, ochronosis, calcium pyrophosphate disease, and monarticular rheumatoid arthritis, it seems clear that either osteoarthritis of the hip does not exist at all as a primary disease entity or, if it does, is extraordinarily rare.