Bone infarcts: Unsuspected gray areas?
There is agreement to label as bone infarcts avascular necrosis (AVN) occurring in the metaphyses or diaphyses of long bones, the terms AVN or osteonecrosis being used at the epiphyses. One might expect bone infarction to hold no mysteries. Oddly enough, however, scientific evidence about bone infarcts is extraordinarily scant. The prevalence of bone infarcts is unknown. The main sites of involvement are the distal femur, proximal tibia, and distal tibia. In patients without sickle cell disease or Gaucher's disease, involvement of the upper limbs and lesions confined to the diaphysis are so rare as to warrant a reappraisal of the diagnosis. Although widely viewed as a generally silent event, bone infarcts causes symptoms in half the cases. Standard radiographs are normal initially then show typical high-density lesions in the center of the marrow cavity. A periosteal reaction is common and may be the first and only radiographic change. Magnetic resonance imaging consistently shows typical features and therefore, in principle, obviates the need for other investigations. Bone infarcts are multifocal in over half the cases and, when multifocal, are usually accompanied with multiple foci of epiphyseal avascular necrosis. Thus, bone infarcts, whose prognosis is good per se (with the exception of the very low risk of malignant transformation), are usually a marker for systemic avascular necrosis. Consequently, patients with bone infarcts must be investigated both for known risk factors and for other foci of avascular necrosis, which may, in contrast, have function-threatening effects.