Intracapsular pressure in congenital dislocation of the hip.

Intracapsular hip joint pressure was measured in six infants with congenital dislocation of the hip (CDH) or acetabular dysplasia with hip joint instability diagnosed at an average of 4.3 months of age (range: 3-8 months). In the extension and neutral rotation position, the mean pressure was 8.9 mm Hg. After reduction, obtaining stability with the hip joints in the "frog-leg" position (i.e., maximum flexion around the axis of the neck of the femur), the mean pressure was 74.6 mm Hg. When obtaining stability with the hip joints in 20 degrees of flexion, abduction, and inward rotation, the mean pressure was 104 mm Hg, and in approximately 20 degrees of flexion, abduction, and forced inward rotation it was 160 mm Hg. We conclude that these rotational positions, often used to retain the joint in CDH or hip joint instability, induce intracapsular pressures that may cause occlusion of epiphyseal-physeal vessels and thus may be responsible for the avascular epiphyseal necrosis and growth disturbance seen in these patients.