Factors affecting visualization of posterior rib fractures in abused infants.

Rib fractures frequently are encountered in abused infants and commonly occur in the posterior rib arcs. Fractures occurring near the costovertebral articulations are rarely identified radiographically in the acute phase, and callus formation usually is the first indication of injury. To assess the factors influencing the visibility of fractures near the costovertebral articulations in abused infants, 103 posterior rib fractures occurring in 16 abused infants were studied radiologically. The plain radiologic studies were correlated with the pathologic findings in 15 ribs from four patients. The limited visibility of fractures relates to (1) the frequent superimposition of the transverse process over the rib fracture site, (2) a fracture line that crosses at an obliquity to the radiographic beam, and (3) nondisplacement of rib fragments due to preservation of the posterior periosteum. Fresh fractures invisible on a frontal projection are clearly defined when the rib is viewed axially with postmortem radiography. These findings explain the reported superior sensitivity of radionuclide bone scans vs radiography in the identification of fresh posterior rib fractures. A knowledge of the factors influencing the visibility of these important injuries is useful in planning an appropriate diagnostic evaluation in cases of suspected infant abuse.