Regeneration after physeal distraction of the radius in sheep.

In 18 sheep, gradual physeal distraction of the distal radius was performed by external fixation. Separation of the physis from the metaphysis occurred in all the sheep. Prior to bone formation, collagen fibers were organized according to the direction of the distraction, and lamellar bone was formed if the collagen bundles were lineally organized. In the area where the collagen was disorganized, and also near the periosteum, woven bone was first formed, which was then remodeled into lamellar bone. In some sheep separate groups of chondrocytes were isolated in the metaphyseal area after the distraction. In 2 animals a double physis was formed in the metaphyseal area. This was obviously due to the separation of proliferative chondrocytes in the metaphysis as a result of distraction. After consolidation of the distraction area, this zone of chondrocytes, located in the metaphysis, was still producing new bone 20 weeks postoperatively.