ACR Codes: 4.4
Of all the injuries observed in child physical abuse, none is more specific than the metaphyseal fracture. First described in 1957 by the eminent pediatric radiologist John Caffey, metaphyseal fracture is virtually pathognomonic of abuse. Kleinman et al coined the term "classic metaphyseal lesion" (CML) to describe the injury. CMLs are relatively common in abused infants and are discovered in 39%-50% of abused children less than 18 months of age. Overall, CMLs most often occur in the distal femur, proximal tibia, distal tibia, and proximal humerus. They are seen almost exclusively in children less than 2 years of age.
The CML is a series of microfractures across the metaphysis; the fracture line is oriented essentially parallel to the physis, although it may not travel the entire width of the bone. Its orientation perpendicular to the long axis of the bone reveals that the precipitating force is a shearing injury across the bone end. Shearing in this manner is a peculiar force for a long bone to sustain, since it is the result of differential horizontal motion across the metaphysis and is therefore not a feature of falls or blunt trauma. The force is generated by manual to-and-fro manipulation of the extremities (eg, holding and shaking an infant by the feet or hands or shaking the infant while he is held around the chest, with the limbs whiplashing back and forth and sustaining horizontal shear forces) Because the wafer of bone that is the fracture fragment may have a very thin center, this region may be radiographically occult. The thicker peripheral rim is more readily visible and appears as a triangular fragment when viewed in profile (commonly referred to as a corner fracture). If the fragment is separated from the remainder of the long bone by a prominent fracture lucency, or if the fracture is viewed at a slightly oblique angle, the thick rim may be visible as a curvilinear structure resembling a bucket handle. Thus, the appearance varies with the length and width of the fracture fragment (ie, how far across the metaphysis the fracture extends), as well as its position at radiography.
Although skeletal injuries rarely pose a threat to the life of an abused child, they are often the strongest radiologic indicators of abuse. In fact, in an infant, certain patterns of injury are sufficiently characteristic to permit a firm diagnosis of inflicted injury in the absence of clinical information. This fact mandates that imaging surveys perfomed to identify skeletal injury be performed with at least the same level of technical excellence routinely used to evaluate accidental injuries. The "babygram" or abbreviated skeletal surveys have no role in the imaging of these subtle but highly specific bony abnormalities.