Hip Involvement in Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease which primarily affects axial skeleton including the sacroiliac joints and spine but also involves other joints. Some patients, however, are mainly affected in the peripheral joints such as the hip and, less commonly, the knee joints. Hip joint accounts for 25–50% in peripheral involvement of AS, 50–90% patients of which have bilateral diseases, leading to stiff hip and loss of joint function. AS was once believed to mainly affect females, but recent studies tend to reveal similar prevalence between males and females. Male patients generally have more progressive spine and hip deformities, whereas females have more peripheral involvement with milder symptoms and thus higher rate of misdiagnosis and underdiagnoses. Young age at onset is a risk factor for severe disease. Loss of hip function and severe pain often lead to remarkable disability.