The Etiology of Osteoarthritis of the Hip

Abstract

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°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 middleaged 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 of Evidence: Level V, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

The prevalence of radiographic femoroacetabular impingement in younger individuals undergoing total hip replacement for osteoarthritis

“…Cam impingement is characterized by a bony prominence at the femoral head-neck junction. With hip flexion or internal rotation, the cam lesion is forced against the acetabular rim, potentially leading to cartilage avulsion and damage [3,4] (Fig. 1a).…”

“…In contrast, pincer impingement involves acetabular over-coverage of the femoral head. Impingement occurs at the limit of hip movement as the femoral head is forced against the protruding acetabulum, leading to circumferential labral injury and cartilage damage [2][3][4] (Fig. 1b).…”

“…1b). Cam impingement is more commonly found in younger athletic males, while pincer impingement occurs typically in middle-aged females [3,5]. Often, patients present with features of both impingement types [6].…”

What Ape Proximal Femora Tell Us About Femoroacetabular Impingement: A Comparison

“…For example, both coxa profunda and coxa recta are morphotypes associated with femoroacetabular impingement [6,7]. However, such variability in the shape of the human proximal femur does not appear to be present in nonhuman apes (Figs.…”

“…1), and some variations (or hip morphotypes) such as coxa profunda and coxa recta (cam type hip) are associated with femoroacetabular impingement and the development of osteoarthrosis [6,7]. Currently, however, this variability is unexplained.…”