The hip joint is a ball-and-socket joint that is comprised of the head of the femur (ball) and the acetabulum (socket). The surfaces of the acetabulum and femoral head are covered with articular cartilage, a shiny, smooth white tissue that enables the joint surfaces to glide over each other with ease. The health of the bone beneath the articular cartilage is important to maintain a smooth, congruent joint surface.
What is avascular necrosis of the hip?
Avascular necrosis of the hip occurs when the blood supply to the femoral head is disrupted, leading to a lack of nutrients and oxygen delivery to the bone. Without these necessities, the bone dies. Over time, the dead bone weakens and eventually collapses, interfering with the articular cartilage on the surface. This leads to progressive osteoarthritis and destruction of the hip that can be painful and disabling.
What are the symptoms of avascular necrosis of the hip?
Avascular necrosis usually presents initially with new-onset hip pain. This may progress to dull aching or throbbing pain in the groin. As the disease progresses, it is more difficult to walk or bear weight on the affected hip. It may take anywhere from a few months to a year for the disease to progress. Early diagnosis is important because some studies have shown better outcomes when treated earlier in the disease process.
Who gets avascular necrosis?
Osteonecrosis can occur in anyone, but it is most common in individuals between the age of 40 and 65. It is also more common in men than women. In many instances, both hips may be affected by the disease.
There have been several risk factors that have been identified for avascular necrosis of the hip. Most commonly, patients who develop avascular necrosis have a history of excessive alcohol use or chronic corticosteroid use. Both substances lead to fatty deposits in the bone marrow which result in decreased blood flow to the bone.
Trauma to the hip such as a dislocation or fracture is another known cause of avascular necrosis. Trauma can damage the blood vessels in the femoral head and disrupt its blood supply.
Although rarer, a handful of medical conditions have also been associated with the development of avascular necrosis. This includes Caisson disease (“the bends”), sickle cell disease, myeloproliferative disorders, Gaucher’s disease, systemic lupus erythematosus, Crohn’s disease, arterial embolism, thrombosis, and vasculitis.
How is avascular necrosis diagnosed?
The diagnosis of avascular necrosis relies heavily on imaging studies. An x-ray of the hip is the initial study to examine the bony structures of the joint. This allows your surgeon to determine if the bone in the femoral head has collapsed and to what degree. A common x-ray finding is a wedge-shaped area of dense, whitish substance in the superior lateral portion of the femoral head.
However, if the x-ray is normal, an MRI of the hip is obtained to look for early signs of avascular necrosis. An MRI has the added advantage of picking up signs of avascular necrosis that would be otherwise missed on x-ray (Image 1 and 2). This is especially helpful in discovering lesions of avascular necrosis that have not yet developed symptoms, as in a lesion on the opposite hip. MRI may also be used to determine how much of the bone is affected.
How is avascular necrosis treated?
Avascular necrosis may be treated non-surgically or surgically depending on the stage of disease. Non-surgical treatment with over-the-counter anti-inflammatory medications, activity modification, and protected weight-bearing with crutches may be appropriate in mild to moderate cases. These options may relieve pain and slow the progression of disease, but surgical options have been shown to be more effective.
The surgical options for avascular necrosis of the hip include core decompression, osteochondral grafting, vascularized fibula graft, and hip replacement:
- Core decompression is a minimally invasive procedure that involves drilling a hole into the femoral head to relieve the pressure within the bone. The decreased pressure allows the vasculature to re-supply the damaged bone. This procedure also creates new channels for blood vessels to supply nutrients and oxygen to the dead bone. Core decompression is most effective in cases that are diagnosed early before the bone collapses.
- Osteochondral grafting involves replacing the dead bone and damaged cartilage with healthy bone and cartilage from another bone in the body (autograft) or from a donor (allograft). This procedure replaces the defect, provides mechanical support, and re-introduces a smooth cartilage joint surface. Stem cells are often extracted from other parts of the body and injected into the joint during this procedure to promote bone and cartilage healing as well as reduce inflammation.
- A vascularized fibula graft involves grafting a segment of the small bone in your leg (fibula) along with its blood supply (artery and vein) and inserting it into the area of osteonecrosis within the femoral head. The artery and vein from the fibula graft is reattached to the blood supply of the hip and provides oxygen and nutrients to heal the area.
- A hip replacement is the most effective treatment in late-stage cases where the bone has already collapsed. This procedure involves removing the damaged femoral head (ball) and part of the acetabulum (socket) and replacing it with prosthetic implants that restore the function of the joint.