Irritable hip and Perthes' disease.

One hundred fifty patients with 160 irritable hip episodes and 120 patients with Perthes' disease who were treated between 1976 and 1986 were compared. The ratio of males to females was 2.1:1 for patients with irritable hip and 3:1 for patients with Perthes' disease. On the average, patients with irritable hip were aged 3 years and patients with Perthes' disease were aged 7 years. The duration of symptoms in patients with irritable hip averaged 6 days and 6 weeks in patients with Perthes' disease. One patient developed Perthes' disease 2 months after the irritable hip episode. The mean intraarticular pressure in 10 of the hip patients was 17 mm Hg in the neutral flexion/extension position. The pressure decreased to a mean of 7 mm Hg at 90 degrees of flexion and increased to 10 mm Hg at 45 degrees and to 16 mm Hg at 30 degrees of flexion. There was a positive correlation between the amount of aspirated fluid and recorded intracapsular pressure. Pressure tamponade in the irritable hip syndrome is probably not responsible for Perthes' disease.