Factors affecting visualization of posterior rib fractures in abused infants

Rib fractures in abused infants commonly occur in the posterior rib arcs. Fractures occurring near the costovertebral articulations are usually identified radiographically only once callus has formed. To assess the factors influencing the visibility of fractures near the costovertical articulations, the authors studied 103 posterior rib fractures occurring in 16 abused infants. Radiologic findings were correlated with CT findings and pathologic material from nine ribs in 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 x-ray beam, and (3) nondisplacement of rib fragments due to preservation of the posterior periosteum. Fresh rib fractures invisible on a frontal projection may be clearly defined on axial CT scans, or on postmortem radiographs. A knowledge of the factors influencing the visibility of these important injuries is useful in planning an appropriate diagnostic evaluation of suspected infant abuse