Osteonecrosis is a condition in which death of a section of bone occurs because of lack of blood supply to it. It is one of the most common causes of knee pain in older women. Women over the age of 60 years of age are commonly affected, three times more often than men.
Osteonecrosis of the knee is most commonly seen in the femoral condyle, usually on the inner side of the knee (the medial femoral condyle). 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.
The exact cause of the osteonecrosis of the knee is unknown. However 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 result in 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.