Healing patterns of metaphyseal fractures.

Metaphyseal fractures having different degrees of stability were produced in rats, rabbits, and dogs. The progress of healing various radiologic patterns, observed by correlated roentgenographic and histologic observations, show that the appearance on radiographs of one or two broad, ill-defined bands of increased density indicates a normal healing process. Cortical healing lags behind cancellous bone healing. No external callus develops. The appearance of two dense, well-defined bars bordering a radiolucent gap indicates delayed union or nonunion and usually can be attributed to instability at fracture site. The appearance of an external callus and the elaboration of a fibrocartilaginous bridging by callus portrays delayed union, secondary to gross instability and/or displacement. Similar patterns appear when there is an avascular fragment, in which case osteogenic activity is limited to one fracture line. Radiologic criteria based on histologic observations permit assessment of metaphyseal fracture healing.