The hip is a ballandsocket joint. Normally, the femoral head is well covered by the hip socket or acetabulum. Hip dysplasia, sometimes referred to as acetabular dysplasia, occurs when one or more areas of the hip joint have not developed properly. The abnormality causes stress on the soft tissue that lines the hip socket and also strains the hip cartilage and bone. If hip dysplasia is not treated, the cartilage may wear away, and arthritis may develop.