Spontaneous Osteonecrosis of the Knee
Diane Wilkinson, M.D.
James Stevan Nagel, M.D.
October 7, 1986
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.
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.
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
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
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
- Aglietti P, Insall JN, Buzzi R, Deschamps G. Idiopathic osteonecrosis of the knee. J Bone Joint Surg (Br) 1983; 65:588-597.
- 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.
- Muheim G, Bohne WH. Prognosis in spontaneous osteonecrosis of the knee. Investigation by radiography. J Bone Joint Surg (Br) 1970; 52:605-612.
- Rozing PM, Insall J, Bohne WH. Spontaneous osteonecrosis of the knee. J Bone Joint Surg (Am) 1980; 62:2-7.
- Collier D, et al. Chronic knee pain assessed by SPECT: comparison with other modalities. Radiology 1985; 157:795-802.
J. Anthony Parker, MD PhD, email@example.com