Histologic evaluation of regenerate bone in cases of limb lengthening by the Ilizarov technique. An experimental study in dogs.

The histology of bone regeneration in cases of limb lengthening was studied in eight adult dogs. Following an osteotomy of the right fibula, an Orthofix (four dogs) or an Ilizarov external fixator (4 dogs) was installed and an osteotomy of the right tibia performed. Lengthening was started seven days after the surgery at the rate and rhythm of 0.5 mm every 12 hours for three weeks and was then followed by compression of 1 mm. The animals were then sacrificed in pairs 3, 6, 9 and 12 weeks after the start of lengthening. Histological evaluation of regenerate bone was performed using hematoxylin and eosin, trichrome and Von Kossa stain (decalcified). New bone at the site of distraction seemed to be formed mostly through intramembranous, and to a lesser extent, through endochondral ossification as evident by the presence of cartilaginous islands within the distraction gap of old specimens. However, these foci of cartilage cells did not have the appearance of growth plates. From the third week of lengthening, collagen fibers were laid down along the longitudinal axis of distraction. Mineralization of these fibers started at the bone ends and during the following weeks, progressed towards the center of the distraction gap. New bone was formed from both the medullary cavity and the periosteum.