DDH is a congenital (present at birth) condition of the hip joint, occurring once in every 1,000 babies. The hip joint is as a ball and socket. In DDH the hip socket may be too shallow. In severe cases the ball of the femur can slip either partially or completely out of the socket. Mild DDH may not be picked up until adulthood when the hip becomes painful. The issue is that with a shallow socket, the forces going through the hip are concentrated over a smaller area, causing increased wear and arthritis.

This is a condition involving the end of the femur (thigh bone), where the epiphyseal plate (growth plate) weakens and the head of the femur (ball) slips downwards and backwards. This leads to the ball not being as circular as it should be, which again leads to increased frictional forces (similar to impingement) in the joint and subsequent wear.

Perthes’ disease affects the head of the femur during childhood; it affects around 1 in every 20,000 children. The blood supply to the growth plate of the bone becomes inadequate and results in the bone and cartilage softening and breaking down, a process called necrosis. This can lead to the head of the femur being deformed or flattened. The effects of this can continue into adulthood and cause osteoarthritis.

Avascular necrosis is a disease where there is cellular death (necrosis) of bone components due to interruption of the blood supply. Without blood, the bone tissue dies and the bone collapses. If avascular necrosis involves the bones of a joint, it often leads to destruction of the joint articular surfaces