Distraction epiphysiolysis as a method of limb lengthening. II. Morphologic investigations.

Distraction epiphysiolysis as a means of lengthening bone has been studied in sheep tibiae by histologic, histochemical and microradiographic and electron microscopic methods. The tibiae have been studied 1, 2, 3 and 4 weeks and 2, 4, 6 and 12 months after the induction of this procedure. Distraction epiphysiolysis occurs in the following stages: development of a fracture along a line dividing the maturing from the hypertrophic chondrocytes, with the formation of a hematoma between the fracture surfaces; downward displacement of the metaphyseal cartilaginous fragment and gradual resorption of the hematoma, which is replaced by fibrous tissue; elongation of the fibrous tissue; with the formation of collagen bundles oriented parallel to the tensile force of distraction; calcification and ossification of these bundles, with the formation of longitudinal and parallel bone trabeculae; development of periosteal bone, which becomes a new diaphyseal shaft. The results show that distraction epiphysiolysis actually lengthens the bone segments; bone structure is completely restored, without serious changes occurring in the soft tissues. Restoration of endochondral ossification in the epiphysis tends to be unpredictable, however, so that the procedure is reliable only in subjects that have almost reached skeletal maturity.