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Your hip is a ball-and-socket joint. The socket is formed by the acetabulum, which is part of the large pelvis bone. The ball is the femoral head, which is the upper end of the femur (thighbone).
The surface of the ball and socket is covered with articular cartilage, a smooth, slippery substance that protects the bones and enables them to glide easily across each other.
Osteonecrosis of the hip occurs in the femoral head, which is the ball of ball-and-socket hip joint.
Osteonecrosis of the hip develops when the blood supply to the femoral head is disrupted. Without adequate nourishment, the bone in the head of the femur dies and gradually collapses. As a result, the articular cartilage covering the hip bones also collapses, leading to disabling arthritis.
Osteonecrosis can affect anyone, but is more common in people between the ages of 40 and 65. Men develop osteonecrosis of the hip more often than women.
In osteonecrosis, the bone in the head of the femur slowly dies
It is not always known what causes the lack of blood supply, but doctors have identified a number of risk factors that can make someone more likely to develop osteonecrosis:
Osteonecrosis develops in stages. Hip pain is typically the first symptom. This may lead to a dull ache or throbbing pain in the groin or buttock area. As the disease progresses, it becomes more difficult to stand and put weight on the affected hip, and moving the hip joint is painful.
It may take from several months to over a year for the disease to progress. It is important to diagnose osteonecrosis early, because some studies show that early treatment is associated with better outcomes.
The four stages of osteonecrosis. The disease can progress from a normal, healthy hip (Stage I) to the collapse of the femoral head and severe osteoarthritis (Stage IV).Reproduced and adapted from Beaule PE, Amstutz, HC: Management of ficat stage III and IV osteonecrosis of the hip. J Amer Acad Orthop Surg 2004; 12: 96-105.
After discussing your symptoms and medical history, your doctor will examine your hip to discover which specific motions cause your pain.
Patients with osteonecrosis often have severe pain in the hip joint but a relatively good range of motion. This is because only the femoral head is involved in the earlier stages of the disease. Later, as the surface of the femoral head collapses, the entire joint becomes arthritic. Loss of motion and stiffness can then develop.
During the exam, the doctor will move your hip in different ways to learn more about your pain.Reproduced from JF Sarwark, ed: Essentials of Musculoskeletal Care, ed 4. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2010.
Imaging studies will help your doctor confirm the diagnosis.
X-rays. X-rays provide images of dense structures, such as bone. X-rays are used to determine whether the bone in the femoral head has collapsed and to what degree.
(Left) An x-ray of a healthy hip joint. (Right) In this x-ray, the osteonecrosis has progressed to collapse of the femoral head.
Osteonecrosis is typically seen as a wedge-shaped area with a dense whitish sclerotic border in the superior lateral portion of the femoral head. On the lateral view, a lucent line called a “crescent sign” can often be seen just below the surface of the femoral head.
Magnetic resonance imaging (MRI) scans. Early changes in the bone that may not show up on an x-ray can be detected with an MRI scan. These scans are used to evaluate how much of the bone is affected by the disease. An MRI may also show early osteonecrosis that has yet to cause symptoms (for example — osteonecrosis that may be developing in the opposite hip joint).
Although nonsurgical treatment options — such as anti-inflammatory medications, activity changes, and using crutches — can help relieve pain and slow the progression of the disease, the most successful treatment options are surgical. Patients with osteonecrosis that is caught in the very early stages (before the femoral head collapses) are potential candidates for hip-preserving procedures.
There are several different surgical procedures used to treat osteonecrosis of the hip.
This procedure involves drilling one larger hole or several smaller holes into the femoral head to relieve pressure in the bone and create channels for new blood vessels to nourish the affected areas of the hip.
When osteonecrosis of the hip is diagnosed early, core decompression is sometimes successful in preventing the collapse of the femoral head and the development of arthritis.
Core decompression is often combined with bone and cartilage grafting to help regenerate healthy bone and support cartilage at the hip joint. A bone graft is healthy bone tissue that is transplanted to an area of the body where it is needed. The tissue may be taken from a donor (allograft) or from another bone in your body (autograft).
There are also several synthetic bone grafts available today.
Another surgical option is a vascularized fibula graft. In this procedure, a segment of bone is taken from the small bone in your leg (fibula) along with its blood supply (an artery and vein). This graft is transplanted into a hole created in the femoral neck and head, and the artery and vein are reattached to help heal the area of osteonecrosis.
Core decompression prevents osteonecrosis from progressing to severe arthritis and the need for hip replacement in some cases. This depends upon the stage and size of the osteonecrosis at the time of the procedure.
Core decompression achieves the best results when osteonecrosis is diagnosed in its early stages before the bone collapses. In some of these cases, the bone heals and regains its blood supply after core decompression. It takes a few months for the bone to heal and, during this time, you will need to use a walker or crutches to avoid putting stress on the damaged bone.
Patients with successful core decompression procedures typically return to walking unassisted in about 3 months and have complete pain relief.
When osteonecrosis is diagnosed after collapsing of the bone, core decompression is not usually successful in preventing further collapse. In this situation, the patient is best treated with a total hip replacement. Total hip replacement is successful in relieving pain and restoring function in the majority of patients with osteonecrosis.