Osteonecrosis of the Knee

Osteonecrosis of the knee is a condition in which bone dies. Bone can due when a section of bone no longer has a blood supply. This is a relatively common cause of knee pain. Most patients who experience this condition are older than 60, and women are affected three times as much as men.

Causes

The knobby part of the knee is most often affected. The exact cause is unknown, but there are theories. A stress fracture in combination with trauma or specific activity is thought to be a cause. It is also thought that if fluid builds up in the bone, this conditions can result from pressure being put on blood vessels, which in turn diminishes circulation.

Certain treatments and conditions may cause this condition. These may include sickle cell anemia, kidney transplant, obesity, lupus and steroid therapy.

Signs and Symptoms

Patients may experience sudden inner knee pain. It may be brought on by a minor injury or specific activity. Pain may increase with activity or at night. The inside and front of the knee may be swollen. Pain may cause a limited range of motion. The affected area may have a heightened sensitivity to touch.

Diagnosis

Diagnosis if often made through x-rays and identifying the signs and symptoms. During stage one, the symptoms are most intense and may last as long as eight weeks, then subside. X-rays are normal so a bone scan is often done.

During stage two, x-rays will show some evidence of osteonecrosis of the knee. A bone scan or MRI is used to confirm the diagnosis. In some cases, a CT scan is done.

During stage three, around three to six months after this condition begins, the damage can be easily seen on x-rays. This means that no other tests have to be performed.

During stage four, the bone will start to collapse. The joint space narrows, the articular cartilage is destroyed, and bone spurs may form.

Treatments

During the early stages, surgery is usually not necessary. If only a small area is affected, only minor treatments may be needed. These may include:

• Pain-relieving medications
• A rehabilitation program to strengthen the thigh muscles
• Reducing pressure on the surface of the joint by using a brace
• Modifying activity to decrease knee pain

If the bone surface is more than half affected, surgery may be necessary. Surgical options include:

• Decreasing any pressure on the surface of the bone with drilling
• Total of unicompartmental knee replacement
• Debridement of the joint
• Taking weightbearing from the affected area

Resources

American Academy of Orthopedic Surgeons. (2007). Osteonecrosis of the Knee. Retrieved on February 28, 2011 from the American Academy of Orthopedic Surgeons: https://orthoinfo.aaos.org/topic.cfm?topic=a00225

Hospital for Special Surgery. (2010). Osteonecrosis of the Knee: An Overview. Retrieved on February 28, 2011 from the Hospital for Special Surgery: https://www.hss.edu/conditions_osteonecrosis-of-the-knee-overview.asp