ABSTRACT
The hip is a ball-and-socket joint formed by the head of the femur and the cup-shaped acetabulum. The joint allows a considerable range of movement in different planes and is still inherently stable because of its bony anatomy and the static and dynamic stabilisers. Avascular necrosis (AVN), or osteonecrosis of the femoral head, occurs because of an interruption in the blood supply to the femoral head, leading to bone death. AVN usually affects men aged 35–45 and is bilateral in over 50% of patients. A weight-bearing anteroposterior radiograph of the pelvis along with a lateral radiograph will show the classical features of AVN, including increased sclerosis in the early stages and the crescent sign indicating subchondral bone resorption. Femoroacetabular impingement has recently been recognised as a cause of hip pain in the young adult and may lead to secondary hip osteoarthritis. Hip dysplasia is a condition in which there is under-coverage of the femoral head, secondary to a shallow acetabulum.
