Coxa magna following transient synovitis of the hip.

In a prospective clinical study of 109 children with transient synovitis of the hip, 32.1% had asymptomatic overgrowth of the femoral head of 2 mm or more (coxa magna) after a follow-up period of one year. Synovial effusion was confirmed with the use of ultrasonography, joint aspiration, or measurement of intraarticular pressure in 93 children and suggested clinically and radiographically only in 16. The most important independent risk factor for later development of coxa magna was radiographic widening of medial joint space with 1 mm or more at admission, which was seen in 42.1% and the presence of which gave a sensitivity of 0.74 and a specificity of 0.73 for coxa magna. At the one-year follow-up examination, the joint space was still wide in 10.1% of the children. The high frequency of coxa magna in these patients and its possible role in the development of degenerative arthritis indicate that transient synovitis of the hip should not be considered a harmless disease until further epidemiologic studies are available.