Spontaneous Osteonecrosis of the Knee

Diane Wilkinson, M.D.

James Stevan Nagel, M.D.

October 7, 1986

CASE PRESENTATION:

A 79 year-old woman noted the relatively acute onset of left knee pain without antecedent trauma. Physical examination revealed tenderness, but no limitation of motion. Her list of medications did not include steroids.

Findings:

Plain radiographs obtained in August 1986 showed changes of osteoarthritis in the medial compartment, and a subchondral lucency (shown by arrow) and surrounding sclerosis, findings suggestive of osteonecrosis. Bone scintigraphy (left medial | anterior | left lateral) performed one month later showed intense uptake of Tc-99m MDP in the medial condyle of the left femur (shown by arrow). These findings are diagnostic of spontaneous osteonecrosis of the knee. She was treated conservatively, as she refused the unicondylar prosthesis recommended by her orthopedic surgeon.

DISCUSSION:

The clinical symptoms and signs of spontaneous osteonecrosis of the knee vary in severity and may mimic other conditions such as meniscal tears and osteoarthritis. In most reports to date, the diagnosis was made in patients with clinical symptoms and the typical radiographic findings which include subchondral lucency in the medial femoral condyle, flattening of the medial femoral condyle, and a narrow zone of increased radiodensity adjacent to the depressed osseous surface. In these patients bone scintigraphy is positive but its role is largely confirmatory. It plays an important role in patients with symptoms and normal or non-diagnostic plain radiographs. In one study of twelve such patients, bone scintigrams showed intense uptake in the affected condyle. In two of the twelve, Craig-needle biopsy was carried out and showed spicules of dead bone without new bone formation. The patients were treatment with protected weight bearing. They became asymptomatic and the bone scans returned to normal in a few months. None of the twelve ever showed characteristic plain radiographic findings. No long term follow-up was available (1).

Bone scintigraphy in this setting may not be specific. A torn meniscus by itself was thought not to cause a positive scan (2,4). A more recent report suggests that SPECT imaging is positive in chronic meniscal tears (5). Older reports (3,4) using rectilinear scanners, subdivided the knee into quadrants and suggested the diagnosis of osteonecrosis as opposed to medial osteoarthritis if the ratio of the medial proximal to the medial distal quadrant was high. Modern planar imaging more easily demonstrates the focality of the lesion. SPECT imaging was more highly sensitive (.91) in identifying osteoarthritis in the patellofemoral compartment. The specificity was 1.00. This report did not deal with SPECT imaging in spontaneous osteonecrosis of the knee, but raises the possibility that it may play a role in demonstrating the focality of the lesion and perhaps increasing specificity. If the lesion can be identified early and therapy instituted, the prognosis should improve, as two studies show that prognosis can be based on the size of the lesion.

In summary, bone scintigraphy plays an important role in the management of patients with suspected osteonecrosis of the knee and non-diagnostic plain radiographs. Early identification of spontaneous osteonecrosis should improve prognosis of this entity.

REFERENCES:

  1. Aglietti P, Insall JN, Buzzi R, Deschamps G. Idiopathic osteonecrosis of the knee. J Bone Joint Surg (Br) 1983; 65:588-597.

  2. Lotke PA, Ecker ML, Alavi A. Painful knees in older patients. Radionuclide diagnosis of possible osteonecrosis with spontaneous resolution. J Bone Joint Surg (Am) 1977; 59:617-621.

  3. Muheim G, Bohne WH. Prognosis in spontaneous osteonecrosis of the knee. Investigation by radiography. J Bone Joint Surg (Br) 1970; 52:605-612.

  4. Rozing PM, Insall J, Bohne WH. Spontaneous osteonecrosis of the knee. J Bone Joint Surg (Am) 1980; 62:2-7.

  5. Collier D, et al. Chronic knee pain assessed by SPECT: comparison with other modalities. Radiology 1985; 157:795-802.

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J. Anthony Parker, MD PhD, jap@nucmed.bih.harvard.edu