Osteonecrosis of the Knee

There are three different types of osteonecrosis of the knee. There is Spontaneous Osteonecrosis of the Knee, Post Arthroscopic Osteonecrosis of the knee, and Secondary Osteonecrosis of the knee. Osteonecrosis is further classified by severity using Ficat Stages of Knee Osteonecrosis. In Stage I, the x-ray appears normal. Stage II, Sclerosis of the condyle is present. In Stage III, the crescent sign is found as well as a subchondral fracture. Stage IV, there is a collapse of subchondral bone.

ficatSpontaneous Osteonecrosis of the Knee typically occurs in females older than 55. Usually one joint and one compartment is affected (medial femoral compartment). No etiology is known. Symptoms typically consist of a sudden onset of severe pain with decreased range of motion as well as swelling in the knee. X-rays will probably appear to be normal. An MRI is helpful, the provider may find a crescent shaped lesion. This conditionspontaneous can cause arthritis. If severe knee pain is present in a middle aged or elderly female patient, and the x-ray is negative, the provider should order an MRI to rule out osteonecrosis of the knee. Treatment consists of protected weightbearing as well as therapy and NSAIDs. An arthroplasty may be required when conservative treatment fails. A unicompartmental knee arthroplasty will be performed for small lesions. A total knee arthroplasty will be completed for large lesions or collapse.

Post Arthroscopy Osteonecrosis of the Knee most commonly occurs in middle aged secondarywomen after a knee arthroplasty. Secondary Osteonecrosis of the knee is common in women under 55 years of age and has associated risk factors. This condition involves more than one compartment or the metaphysis of the knee. Secondary Osteonecrosis occurs bilaterally in 80% of cases and multifocal lesions may be seen. There is a cause for Secondary Osteonecrosis of the knee, which is why it can be bilateral, multiple, and everywhere. Risk factors include:

  • Alcohol use
  • Sickle cell disease
  • Steroid usedissecans
  • Trauma
  • HIV medications
  • Gaucher Disease


These patients should be screened for other joint involvement. The lesion is a subcondylar insufficiency fracture and the patient will have severe pain with weight bearing either standing or sitting. An x-ray may show a wedge-shaped lesion and MRI is the better study. A differential diagnosis is Osteochondral Dissecans, which is located in the lateral aspect of the medial femoral condyle in younger patients. Other differentials include: Occult trauma, bone bruise and overuse, as well as transient osteoporosis which is found more in middle-aged men and usually in the hip rather than the knee. Treatment consists of NSAIDs, a decrease in activity and weightbearing, and physical therapy. A scope surgery may be necessary to remove loose fragments or core decompression for lesions not extending to the joint. An Osteocondylar allograft may be performed for large, painful lesions in younger patients. A total knee replacement may be done for larger lesions, for collapse, or if multiple compartments are involved. Conservative treatment is not as successful with secondary avascular necrosis. Without surgery, secondary AVN will advance to osteoarthritis. Bisphosphonates have no effect on knee osteonecrosis.

Osteonecrosis of the Hip

Osteonecrosis or Avascular Necrosis of the hip is death of a segment of bone in the femoral head due to disruption of the blood supply. The etiology of this condition is not fully understood. There are several risk factors associated with osteonecrosis of the hip. The condition occurs bilaterally in about 80% of patients. It is important for the physician to check both hips, even if one is asymptomatic. An early diagnosis is important because during the early stages of osteonecrosis, a femoral head preserving procedure can be done. In the late stages of osteonecrosis, the femoral head collapses and cannot be saved. The femoral head may need to be replaced. Obtain AP and Frog Leg Lateral views of the hip. The Frog Leg Lateral view will show the crescent sign.

An MRI is the imaging of choice, especially when the patient has persistent hip pain, the radiographs are negative, and the diagnosis of osteonecrosis is suspected.

osteonoThe Ficat Classification is a commonly used system to stage osteonecrosis of the hip. Stage I classifications will have a normal appearing x-ray and an MRI will detect the lesion; changes in the marrow. Stage II classifications are identified by sclerosis and cyst formation. Characteristics of the Stage III classifications are a subchondral fracture and the appearance of a crescent sign and flattening of the femoral head. Stage IV classifications will show advanced lesions with arthritis, osteophyte formation, and a loss of the joint space.



For early stages of osteonecrosis of the hip, initial trial of nonsurgical treatment is usually done. Surgery may be needed if nonsurgical methods are not successful. Nonoperative treatment typically consists of bisphosphonates.

femoral head collapsedThese drugs may be used before the femoral head collapses and are still in the experimental stages. In regards to traditional surgical treatment, when the lesion is small a head preserving procedure can be done. For stages I & II, a core decompression is used. The surgeon can make a single large hole or multiple small holes in the femoral head. It decompresses the head and stimulates a healing response. The lesion is done anteriorly and superiorly.

bonegraft222If the surgeon chooses to perform a core decompression with bone graft, they will debride the necrotic area and insert the bone graft into the open space. Vascularized Fibular Grafts are done in younger patients. Complications include: donor site pain and leg dysfunction as well as tibial stress fractures on the side the graft was taken. Stages III and IV will require a total hip arthroplasty (cementless cup and stem) or total hip resurfacing; however, resurfacing is not commonly used. A total hip replacement is considered to be the traditional procedure for advanced stages of osteonecrosis of the hip. Total hip resurfacing is considered to be controversial because the patient will need adequate bone stock to support the femoral component. The result is not as good when compared with a patient with osteoarthritis.totalhip