Avascular necrosis of the femoral head (ANFH) is a degenerative condition which causes the upper ends of the thigh bones (femurs) to break down due to a disrupted blood supply and poor bone repair. It can lead to pain and limping, hip collapse, and cause the legs to be of unequal length.

The development of ANFH is associated with steroid use, alcohol use, smoking, auto-immune disorders, and other medical conditions such as sickle cellanemia. Less commonly, ANFH can occur as the result of trauma to the hip, such as a hip fracture or hip surgery. Around 20,000-30,000 cases are reported each year in the United States.

This condition mainly affects young, active adults, but can occur in children as well. In children, ANFH is known as Legg-Calves-Perthes disease. Most people with ANFH do not have a family history of this condition, but there are some very rare inherited forms of ANFH.

ANFH is usually diagnosed by X-rays or an MRI. Treatment depends on how much damage is present in the bone, and may involve surgery. Total hip replacement is an option for those with advanced ANFH. Early diagnosis is associated with a better outcome, but is difficult because ANFH doesn’t cause any symptoms in its earliest stages.

Although rare, there are some families that have an inherited form of ANFH. Genetic changes in the type II collagen gene (COL2A1) cause ANFH in a few families. This gene is responsible for making a protein that helps build cartilage. One other family was found to have a genetic change in the transient receptor potential vanilloid 4 gene (TRPV4). This gene makes a protein that helps regulate blood flow.

In the non-inherited types of avascular necrosis of the femoral head, the cause is not clear. These are some of the factors have been associated with an increased chance to get ANFH:

• Steroid use
• Alcohol use
• Chemotherapy
• Auto-immune disease
• Medications that suppress the immune system
• Sickle cellanemia and other disorders of the blood
• Disorders that affect how the blood clots
• Too much fat in the bloodstream (hyperlipidemia)

ANFH can also develop in a person who has had a hip injury (like a fracture or dislocation) or hip surgery.

Most cases of avascular necrosis of the femoral head (ANFH) are not inherited in families. In a few rare families, ANFH is inherited in an autosomal dominant pattern. All individuals inherit two copies of each gene. In inherited ANFH, an individual has a disease-causing mutation in only one copy of the gene that causes the person to have the disease. The mutation can be inherited from either parent. There is nothing either parent can do, before or during a pregnancy, to cause a child to have this.

Each child of an individual with an autosomal dominant condition has a 50% or 1 in 2 chance of inheriting the mutation and the condition. Offspring who inherit the mutation will have the condition, although they could be more or less severely affected than their parent.