When disease or injury prevents the blood supply from flowing freely to a bone, cells in the bone begin to die. As the bone withers, the surrounding cartilage begins to deteriorate, producing pain and other symptoms. This condition, called avascular necrosis or osteonecrosis, is most commonly found in the top of the thighbone. It usually strikes between the ages of 30 and 60, but can affect anyone at any age. The disease, which has many causes, gets worse over time.
Avascular necrosis of the hip occurs when blood flow to the top portion of the thighbone (femur) is interrupted. The affected portion of the bone consists of the head (the ball-shaped piece of bone that fits into the socket of the hip) and neck (the portion of the thighbone just below the head). When it’s deprived of blood, this part of the bone begins to “die,” breaking down and causing the cartilage on top of it to collapse.
Avascular necrosis can follow a hip fracture or a hip dislocation. It can also result from diabetes, sickle cell anemia, kidney disease, alcoholism, gout, and Gaucher’s disease (a hereditary disorder that causes many problems, including erosion of the outer layer of the long bones and pelvis). High doses or prolonged use of steroid medications can lead to the problem. So can decompression sickness (which occurs when a person moves from a high-pressure environment to a low-pressure environment, as when a deep-sea diver ascends to the surface). Sometimes, no cause can be found.
Although rest and exercise can sometimes heal the affected portion of bone, surgery is usually needed.
In as many as 80% of patients with early disease, an operation called core decompression can spark regeneration of the bone. In this procedure, the surgeon drills out the damaged section of bone up to the head of the femur. This opens up channels for blood vessels to reach the diseased area and foster the production of new bone. Hip pain is relieved, and as many as 75% of patients avoid joint replacement later on.1
Early in the disease, osteotomy has been used to redistribute weight and prevent collapse and deformation of the femoral head. In patients with large areas of dead bone, however, osteotomy may hinder bone healing. In those patients—as well as for those with osteoarthritis or pain unrelieved by other treatments—total hip replacement is most often the treatment of choice.