Experimental lengthening of tibial diaphysis: gap healing with or without gradual distraction.

Stepwise distraction of the rabbit tibia after a transverse diaphyseal osteotomy was performed in an external fixator. The goal was to clarify the fine-structural parameters of long-bone lengthening. The tibias were vertically cut and studied 5 weeks after the osteotomy, and the specimens with an initial gap without further lengthening were compared with those with a gap and stepwise distraction. The role of periosteal bone induction was essential for the ossification of a growing gap, whereas the ossification of a simple gap proceeded equally by the endosteal and periosteal routes. The distraction resulted in vertical organization of the premature callus tissue at the proximal pole of the distracted gap, while the distal part of the gap area was deficiently filled by endosteal bone but preliminary fixed by a bridge of periosteal callus tissue.