Osteonecrosis of the Knee

What is osteonecrosis?

Osteonecrosis is a condition in which death of a section of bone occurs because of lack of blood supply to it. It is a common causes of knee pain in older women over the age of 60 years three times more often than men.

Osteonecrosis is most commonly seen in the medial femoral condyle (inner side of the knee). However, the condition can also occur on the outside of the knee (the lateral femoral condyle) or on top of the shin bone (the tibial joint surface), known as the tibial plateau.

What are the causes of osteonecrosis of the knee?

The exact cause is unknown. One of the theories suggests that a stress fracture or trauma results in altered blood supply to the bone. Another theory says that fluid build-up within the bone increases the pressure on the blood vessels resulting in decreased circulation. If the condition is not diagnosed and treated early, it can sometimes proceed to severe osteoarthritis. Certain conditions and treatments that are associated with osteonecrosis of the knee are obesity, sickle cell anaemia, lupus, kidney transplants, and steroid therapy. Steroid-induced osteonecrosis affects multiple joints and can be seen in younger patient groups.

What are the symptoms of osteonecrosis of the knee?

Osteonecrosis in the knee results in quite sudden onset of pain inside the knee that is often activated with a specific activity or minor injury. The pain worsens with activity and at night. Osteonecrosis may also cause swelling of the knee and sensitivity to touch and pressure, and can result in limited motion due to pain and swelling.

There are four stages of development of osteonecrosis of the knee which can be distinguished by symptoms and X-rays.

  • Stage I: The symptoms are most intense in the earliest stage, and may subside in 6 to 8 weeks. In this stage, the X-rays are normal; a positive bone scan may be required to make the diagnosis. Treatment for Stage I disease is non-surgical, focusing on pain relief and protected weight-bearing.
  • Stage II: This stage follows in a couple of months and the X-rays will show flattened edges of the once rounded thighbones. An MRI, CT, or bone scan may be utilized to diagnose the condition. Healing can still occur in this stage.
  • Stage III: At this stage, the condition becomes clearly visible on X-rays and no other diagnostic tests are required. At this point the bone itself may begin to decay away, and cartilage covering the bones loosens from other segments of the leg. Surgical treatments are considered at this stage.
  • Stage IV: In this stage, the bone collapses, joint space narrows, bone spurs form, and the articular cartilage is destroyed. The only treatment at this point is joint replacement surgery.

What are the treatment options for osteonecrosis of the knee?

In the early stage of the disease, non-surgical treatment options that include anti-inflammatory medications, braces, strengthening exercises for thigh muscles, and activity modification may be needed to reduce the knee pain.

Surgical treatment is considered in advanced stages where the bone surface is affected. Surgical treatment options include:

  • Arthroscopic debridement or cleansing of the joint
  • Drilling the area of osteonecrosis of the knee to decrease pressure on the bone surface and promote revascularization of the "dead" bone
  • Procedures to lessen the weight from the affected area
  • Unicompartmental or total knee replacement

We will discuss all the surgical options and may recommend the one appropriate for you.