In acetabular dysplasia, the acetabulum (socket) is too shallow or deformed. The acetabular cup is the component which is placed into the acetabulum (hip socket). The bony surfaces of the femur head and of the acetabulum are covered by cartilage. In this position the ligament also keeps the femoral head pressed into the acetabulum. The acetabulum (cotyloid cavity) is a concave surface of a pelvis. This is what holds the head of the femur securely in the acetabulum. The pedicels of the ilium are short, resulting in a low axially long acetabulum. Anterior to the acetabulum, the integumental surfaces are devoid of spines. The labrum lines the circumference of the acetabulum to provide stability and shock absorption. The pubic branches supply the pelvic surface of the acetabulum. They join each other in a Y-shaped portion of cartilage in the acetabulum. The superior portion of this bone forms approximately one third of the acetabulum. Protrusio acetabuli is an uncommon defect of the acetabulum. The acetabulum, the hip-joint, is open. The caput is not deeply and tightly held by the acetabulum.