Hip osteonecrosis, also called avascular necrosis, is a problem with the blood supply to bone of the hip joint. This condition occurs when there is an interruption of the blood supply to the head of the femur (the ball, of the ball-and-socket hip joint). The lack of normal blood supply to the bone cells causes a decrease in delivery of oxygen and nutrients to the bone, and the bone cells subsequently die. When the bone cells are damaged, the strength of the bone is greatly diminished, and the bone is susceptible to collapse.
Causes of Hip Osteonecrosis
No one know exactly what causes hip osteonecrosis. When hip osteonecrosis occurs, the bone collapses and the joint surface, the cartilage, looses its support. Because the cartilage looses the support of the bone underneath, the joint surface is quickly worn away, and arthritis quickly progresses.
Most patients with hip osteonecrosis are associated with either alcoholism or steroid use. Other risk factors for developing hip osteonecrosis include sickle cell disease, trauma to the hip (dislocation or fracture), lupus, and some genetic disorders.
Symptoms of Hip Osteonecrosis
Hip osteonecrosis usually has few warning signs. Patients often complain of new onset hip pain and difficulty walking. Common symptoms of hip osteonecrosis include:
- Aching pain in the groin
- Pain with movement of the hip
- Difficulty walking or limp
The two tests that are most helpful in diagnosing and treating hip osteonecrosis are x-rays and MRIs. The x-ray may be completely normal, or it may show severe damage to the hip joint. If the x-ray is normal, an MRI may be performed to look for early signs of hip osteonecrosis.
Treatment of Hip Osteonecrosis
Treatment of hip osteonecrosis is difficult because the problem tends to progress quickly despite intervention. In the early stages of hip osteonecrosis, crutches and anti-inflammatory medications can be helpful.
Surgical options in the early stages of hip osteonecrosis include hip decompression and bone grafting. Hip decompression is done to relieve increased pressure within the femoral head that may be contributing to the lack of normal blood flow. A hip decompression is done with the patient asleep in the operating room. Small holes are drilled into the area of hip osteonecrosis to relieve the pressure within the femoral head. The vascularized bone graft moves healthy bone from the lower leg (along with the blood vessels attached to the bone), and places this into the area of hip osteonecrosis. The goal of this surgery is to deliver normal blood flow to the affected hip. Surgeons have also experimented with other types of graft (including cadaver bone and synthetic grafts) to stimulate healing of the bone in the femoral head. These procedures are done only in the early stages of hip osteonecrosis; if the cartilage has already collapsed, they will be ineffective.
The most common surgical treatment of hip osteonecrosis is total hip replacement. If there is damage to the cartilage of the joint, then hip replacement is probably the best option. While hip replacement works well, the replacements will wear out over time. This presents a significant problem in young patients diagnosed with hip osteonecrosis. Another option for younger patients is called hip resurfacing surgery. This procedure is similar to a standard hip replacement, but removes less normal bone.
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CJ Lavernia, RJ Sierra, and FR Grieco "Osteonecrosis of the femoral head" J. Am. Acad. Ortho. Surg., Jul 1999; 7: 250 - 261.