The hip joint is a ‘ball and socket’ joint. The top of the leg bone is rounded and fits into a cup shaped socket in the hip bone. All bones need a blood supply, and the ball of the hip joint gets its most of its blood supply from the bone below it through several small blood vessels in the upper leg bone (femur).
The term ‘avascular’ means without blood supply, and necrosis means the bone or tissue dies, in this case because of no blood supply. The bone cells die and this causes the ball portion of the joint to die. Over time the normally round ball may flatten and collapse.
The pain from AVN often is felt in the groin area at the top of the leg. It usually is worse standing and walking. It begins gradually and slowly increases as the damage worsens. Much of the pain is relieved sitting or lying down unless the disease is in its late stages.
Injuries may damage the fragile arteries taking blood into the ball (the femoral head). Other risk factors for AVN of the hip include long term use of prednisone (a cortisone-like medicine), sickle cell disease, excessive alcohol consumption, autoimmune diseases, small blood clots or even air bubbles (in scuba divers who get ‘the bends’).
X-rays at first may be normal, but in the later stages may show the ball has become damaged and flattened on the top. If the joint seems tender and avascular necrosis is thought to be possible, a test called a bone scan may be ordered. MRI scans also may show early bone changes due to avascular necrosis.
Unfortunately avascular necrosis may be difficult to cure. Non-steroidal anti-inflammatory medications such as ibuprofen or naproxen may be helpful for pain relief. Resting the leg is usually suggested, with limited weight bearing. In the early stages (especially in younger patients), several types of surgical procedures may be attempted to improve reduce blood supply which may be successful. In particular, a procedure called a core decompression where a plug of bone is removed creating a hole into the ball may be tried. If the disease is in the late stages, and the symptoms are severe and unresponsive to other treatments, a partial or total hip replacement may be necessary.