Avascular necrosis (AVN) is a generic term that refers to death of bone due to a lack of blood supply. It is also called osteonecrosis. Avascular necrosis of the hip occurs when there is weakening of the bone and subsequent collapse and deformity of the femoral head. If left untreated, arthritis and chondrolysis can occur. AVN in adolescence is frequently referred to as Adolescent AVN and in children is named Perthes Disease.
In both AVN and Perthes Disease, the femoral head loses part (or all) of its blood supply and part (or all) of the bone of the femoral head dies. This dead bone is referred to as necrotic bone. The exact nature of this loss of blood is not well-understood but variety of risk factors have been identified, including:
- Hematologic Diseases (leukemia, lymphoma)
- Dysbaric Disorders (decompression sickness, "the bends")
- Marrow-replacing Diseases (Gaucher's Disease)
- Sickle Cell Disease
Avascular necrosis has also been linked to corticosteroid use and alcoholism.
Due to a loss of blood supply to the femoral head, the femoral head gradually weakens and may collapse, leading to deformation of the joint surface. This occurs because the cells that remove dead bone (osteoclasts) remove the "support structure" for the femoral head. If too much bone is removed before the cells can produce new bone (osteoblasts), the femoral head will slowly collapse and the normally sperhically-shaped femoral head will become flattened to an egg-shaped configuration.
There are approximately 20,000 new cases of avascular necrosis reported in the United States each year, and AVN accounts for 10% of total hip arthroplasties performed. It is more common in men than women and bilateral (both hip) involvement is quite common (>80% incidence). When multiple joints are affected, it is termed multifocal osteonecrosis. This, however, is quite rare (<3% incidence).
In the early stages of AVN, the patient will not feel pain and will likely be unaware of the disease progression. Patients will usually present with pain, usually located in the hip, and usually during activities like climbing stairs or inclines, and high-impact activities. Pain will continue to increase as the bone collapses.
Treatment involves preserving the function of the hip joint through reconstructing and preserving the deformed femoral head and ROM treatment to maximize motion and strength of the joint.