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 comp artment in the absence of any identifiable precipitating factor. Sugge stive changes were seen on initial roentgenograms in only one case, wh ereas increased radionuclide uptake was a consistent finding on the bo ne scan. The diagnosis was established only by magnetic resonance imag ing in five cases. All six patients were women and four were older tha n 75 years. Two patients had a history of osteoporotic fractures, one had laboratory test evidence of osteomalacia and one had recurrent ins ufficiency fractures mistakenly ascribed for several years to migrator y transient osteoporosis. Bone density was subnormal in five of the si x patients. Rest and standard analgesics consistently ensured a favora ble outcome within three to four weeks. To our knowledge there have be en no previous reports of stress fractures of the medial femoral condy le. These lesions may be underdiagnosed since they are easily mistaken for primary osteonecrosis in the absence of magnetic resonance imagin g. Primary osteonecrosis of the femoral condyle shares several feature s with insufficiency fractures, including predominance in elderly wome n with factors responsible for mechanical stress (varum, obesity, triv ial trauma), mechanical pain, and increased radionuclide uptake. Becau se some cases of primary osteonecrosis may be secondary to undiagnosed stress-related microfractures, early diagnosis and elimination of wei ght bearing are essential.