Distraction effects on the physis in rabbits

Gradual physeal distraction by external fixation was performed on the distal femur in 19 growing rabbits. The rate of distraction was 0.5-1 mm once daily. Distraction was continued for 1-21 days until killing. Lengthening of the femur and latitudinal growth of the distraction area were measured in radiographs. Morphologic changes in the physes were studied in histologic preparations. The length gained by distraction was maximally 5 mm. Latitudinal overgrowth was noted in specimens distracted for more than 13 days. Hyperplasia of the hypertrophic chondrocyte zone was seen after 1 day of distraction. Separation of the epiphysis from the metaphysis, mostly through the hypertrophic zone, occurred in 11 specimens. Both hyperplasia and separation were often seen in the same physis. In the separation gap, early signs of bone formation into a collagen frame were seen from the 7th day on. An accessory physis, located in the metaphysis and apparently growing interstitially, was noted in 1 specimen.