Insufficiency fractures of the medial femoral condyle.

We report six cases of insufficiency fractures of the medial femoral condyle responsible for severe mechanical pain in the medial knee compartment in the absence of any identifiable precipitating factor. Suggestive changes were seen on initial roentgenograms in only one case, whereas increased radionuclide uptake was a consistent finding on the bone scan. The diagnosis was established only by magnetic resonance imaging in five cases. All six patients were women and four were older than 75 years. Two patients had a history of osteoporotic fractures, one had laboratory test evidence of osteomalacia and one had recurrent insufficiency fractures mistakenly ascribed for several years to migratory transient osteoporosis. Bone density was subnormal in five of the six patients. Rest and standard analgesics consistently ensured a favorable outcome within three to four weeks. To our knowledge there have been no previous reports of stress fractures of the medial femoral condyle. These lesions may be underdiagnosed since they are easily mistaken for primary osteonecrosis in the absence of magnetic resonance imaging. Primary osteonecrosis of the femoral condyle shares several features with insufficiency fractures, including predominance in elderly women with factors responsible for mechanical stress (varum, obesity, trivial trauma), mechanical pain, and increased radionuclide uptake. Because some cases of primary osteonecrosis may be secondary to undiagnosed stress-related microfractures, early diagnosis and elimination of weight bearing are essential.