Coxa magna after open reduction for developmental dislocation of the hip.

We studied coxa magna after open reduction of developmental hip dislocation, including the etiology, incidence, and influence on the long-term results and acetabular development. Forty-seven hips in 47 patients were radiographically examined for at least 10 years, and another 20 hips in 20 patients were examined arthrographically at an early stage after open reduction. At follow-up, the incidence of coxa magna, which was defined as a femoral head with a size > or = 20% greater than the opposite side, was 34.0%, and that seemed to be one of factors that worsened the long-term results. One of the most important causes of coxa magna is to overwiden the acetabular capacity by excising the limbus; another cause is the surgical invasion and synovitis of the hip joint after operation.