Joint, Ligament and Muscle Disorders

Hip Osteonecrosis

Anatomy

The 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 formed by the femoral head, which is the upper end of the thighbone, or femur. The surfaces of both the ball and socket are covered with articular cartilage, a smooth tissue that cushions the ends of the bones and enables them to move with ease. The hip joint is surrounded with synovial membrane, a thin tissue that produces a small amount of fluid to lubricate the cartilage and eliminate nearly all friction during hip movement. The ball and socket are connected by bands of tissue called ligaments (the hip capsule) that provide stability to the joint.

Description

Osteonecrosis of the hip is a painful condition that 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. This causes the articular cartilage covering the hip bones to also collapse, leading to disabling arthritis and destruction of the hip joint.

Although osteonecrosis (also called avascular necrosis or aseptic necrosis) can occur in any bone, it most often affects the hip. Every year, more than 20,000 people enter hospitals for treatment of osteonecrosis of the hip and in many cases, both hips are affected by the disease.

Risk Factors

Osteonecrosis affects people of all ages; however, it most commonly occurs between the ages of 40 and 65, and men develop it more often than women. Although the cause of the interruption to the femoral head's blood supply is not always known, there are several risk factors that can increase the likelihood of developing this disease.

• Injury—Hip dislocations, hip fractures, and other injuries can cause damage to blood vessels and impair circulation to the femoral head.
• Alcoholism
• Corticosteroid medications—Steroids are commonly used to treat a variety of diseases, such as asthma, rheumatoid arthritis, and systemic lupus erythematosus. Research has shown that there is a connection between long-term steroid use and the development of osteonecrosis, however the reason for this has not been determined.
• Other medical conditions—Osteonecrosis is associated with other diseases, including Caisson disease (diver's disease or "the bends"), sickle cell disease, myeloproliferative disorders, Gaucher's disease, systemic lupus erythematosus, Crohn's disease, arterial embolism, thrombosis, and vasculitis.

Symptoms

Osteonecrosis develops in stages. The first symptom is typically hip pain, which may lead to a dull ache or throbbing pain in the groin or buttock area. As the disease progresses, it becomes increasingly difficult to stand and put weight on the affected hip, and moving the hip joint is painful. The amount of time required for the disease to progress through these stages varies from several months to over a year, however, some studies show that better outcomes are associated with early diagnosis and treatment.

Diagnosis

After discussing your symptoms and medical history with you, your orthopaedic surgeon will examine your hip to determine what specific motions cause you pain. Some imaging tests may be needed to help your doctor confirm the diagnosis.

• X-Rays—By creating images of dense structures, such as bone, X-rays can be used to help your physician determine whether the bone in the femoral head has collapsed and if so, to what degree.
• Magnetic resonance imaging (MRI) scans or ultrasounds—Early changes in the bone that may not show up in an X-ray can be detected with an MRI scan. An MRI may show early osteonecrosis that has yet to cause symptoms (for example, whether osteonecrosis is developing in the opposite hip joint) and can also be used to evaluate how much of the bone has been affected by the disease.

Nonsurgical Treatment

Although nonsurgical treatment, such as medications or use of crutches, can help relieve pain and slow progression of the disease, the most successful treatment options are surgical. Patients with osteonecrosis that is diagnosed in the very early stages of the disease (prior to femoral head collapse) are good candidates for surgical hip preserving procedures.

Surgery

• Core decompressionstrong> - One large hole or several smaller holes are drilled 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, this procedure is often successful in preventing collapse of the femoral head and the development of arthritis. Core decompression is often combined with bone grafting to help regenerate healthy bone and support cartilage at the hip joint.

  Many bone graft options are available today, including autografts, allografts and fascularized fibula grafts.

  Autograft: This is the standard technique for a bone graft. During an autograft, healthy bone tissue is removed, or harvested, from one area and grafted (transplanted) to another part of the body.

  Allograft: Many surgeons use bone that is harvested from a donor or cadaver, typically acquired through a bone bank. Like other organs, bone can be donated upon death. There are also several synthetic bone grafts available today.

  Vascularized fibula graft: This is an involved procedure in which a segment of bone is taken from the small bone in the leg (fibula) along with its blood supply (an artery and vein). The graft is transplanted into a hole that has been created in the femoral neck and head, and the artery and vein are reattached to promote healing in the area of osteonecrosis.

• Total hip replacement—During total hip replacement, artificial implants are used to replace damaged cartilage and bone. This is typically the most successful treatment for patients with osteonecrosis that has advanced to femoral head collapse, and it is effective in relieving pain and restoring function in 90-95% of patients. Total hip replacement is considered by many to be one of the most successful operations in all of medicine.
• Risks and complications—With any surgery, there are some risks, and these vary from person to person. Complications are typically minor, treatable and unlikely to affect your final outcome. Your orthopaedic surgeon will speak to you prior to surgery to explain any potential risks and complications that may be associated with your procedure.

Outcomes

Core decompression prevents osteonecrosis from progressing to severe arthritis and the need for hip replacement in 25-85% of cases, depending upon the stage and size of the osteonecrosis at the time of surgery. In many of these cases, the bone heals and regains its blood supply. During the several months required for the bone to heal, a walker or crutches will be needed to prevent putting stress on damaged bone. Following successful core decompression procedures, patients typically resume walking unassisted in about 3 months and have complete pain relief.

Core decompression achieves the best results when osteonecrosis is diagnosed in its early stages, before the bone collapses. When osteonecrosis is diagnosed after collapse of the bone, the best option is a total hip replacement, which relieves pain and restores function in 90-95% of patients.