Protrusio acetabuli in seronegative spondyloarthropathy.

Protrusio acetabuli (PA) is a complication of many disorders involving the hip joint. Its frequency and clinical features in seronegative sponyloarthropathy (SNSA) are unknown. The prevalence and characteristics of PA were studied in 50 adults and 25 children with SNSA (40 ankylosing spondylitis, 24 psoriatic arthropathy, and 11 Reiter's syndrome).