Summary:We attempted to clarify experimentally the effect of hip joint incongruity on the necrotic femoral head. Twenty‐four immature rabbits were divided into three groups: group I (12 rabbits), interruption of the epiphyseal artery and immobilization of the knee in extension for inducing subluxation of the hip; group II (six rabbits), interruption of the epiphyseal artery; group III (six rabbits), opening of the capsule (with preservation of the epiphyseal artery) and immobilization of the knee in extension. Radiographic examination of the hips of the rabbits in group I showed severe deformation of the necrotic femoral head with subluxation. These radiographic findings appeared similar to those of human hip joints affected with Perthes' disease.