The effect of distraction upon bone, muscle, and periosteum.

Bone lengthening was achieved on rabbit tibias by means of callus distraction (callotasis) using a dynamic external fixator. The periosteum and the muscle fascia were labeled with metal markers; changes in position of these markers during slow progressive distraction were monitored by soft radiography. During the waiting period before commencing distraction, the periosteal markers around the osteotomy site were elevated from the bone surface by newly formed external callus. There was an apparent lag period until the periosteal reaction occurred after osteotomy. Subperiosteal callus was first formed in an uncalcified state and subsequently became calcified. As distraction began, longitudinal migration of the periosteal markers was observed. It appears that the periosteum slides over the bone cortex, mitigating local stretching of the muscle around osteotomy site. The elongation of muscle occurs throughout the muscle substance and not simply at the site of osteotomy.