Hip Avascular Necrosis (AVN): Overview

Hip Avascular Necrosis (AVN): Overview

Avascular necrosis, A V N for short, also referred to as osteonecrosis of the hip, is a condition where there is a lack of blood supply to the ball of the thigh bone, known as the femoral head. Without nutrients that the blood supply provides, the bone cells in this area start to die off. This leads to changes of the bone structure and eventually arthritis.

Avascular necrosis can affect other joints in the body too, but the hip is most common. Ten thousand to 30,000 new cases of avascular necrosis of the hip are diagnosed each year in the United States. Although people of all ages are affected by AVN, it most commonly occurs between the ages of 30 and 65 years old.

As previously mentioned, avascular necrosis results from the lack of blood supply to the hip joint. There have been numerous risk factors identified that result in this disruption, including traumatic injury to the hip joint, such as a break in the upper thigh bone, or dislocation of the hip joint.

Other risk factors include alcohol abuse, high-dose steroid use, autoimmune diseases, or any other underlying medical condition which can result in compromise to the blood supply in the body. However, in a number of cases, a specific cause is not identified.

Let us take a closer look at the anatomy of the hip joint. The hip joint is a ball and socket joint, the upper portion of the thigh bone, the femur, has a ball-shaped projection referred to as the femoral head. The femoral head is surrounded by the cup part of the pelvis called the acetabulum.

The surface of both the ball and socket are covered with smooth connective tissue called cartilage. Cartilage surrounds both the ball and socket, which allows for the hip joint to move smoothly and pain-free, since it does not contain any nerve fibers.

The blood supply to the femoral head is supplied by small arteries called retinacular vessels. In avascular necrosis, blood flow to these small arteries is disrupted and the bone in the femoral head starts to collapse.

As the bone cells die off due to lack of support by the underlying bone, the cartilage surface becomes irregular, leading to collapse and eventually arthritis. However, this process does not happen overnight and usually will take months to years.

In fact, patients with AVN of the hip may not have symptoms at first. As the condition progresses, hip pain begins, most commonly in the groin. However, pain can also occur in the thigh, knee, buttock, or low back. This pain can occur either with activity or even at rest.

When seeing a healthcare provider, they will carefully consider the patient's medical history. During a physical exam, the provider will watch the patient walk to see if there is a limp. They will also assess the motion of the hip.

Often pain will be provoked with movement of the hip, which also may be limited as the condition progresses. For a provider to make the diagnosis of avascular necrosis, imaging studies are required.

X-rays are the initial imaging test ordered, which in later stages, signs of bone collapse can be identified. In this example you can see the blue line outlining the normal shape of the femoral head. Now in red, we can see how the femoral head becomes misshapen as bony collapse occurs.

Early on, there may be no signs detected on x-ray. MRI studies are best for early detection where the lack of blood supply to the ball of the hip joint can be seen. After thorough review of the imaging tests and correlation with the patient's medical history and symptoms, the doctor will determine and communicate the next course of action for treatment.