Histomorphometry of distraction osteogenesis during experimental tibial lengthening

Objectives: The aim of the current study was to analyze distraction osteogenesis histomorphometrically to investigate the amount of enchondral ossification adjacent to intramembranous ossification. Study Design: Species-specific, longitudinal time study. Methods: Lengthening of 25% of the right tibia was performed in 24 beagle dogs by callus distraction after osteotomy and application of a ring fixator. Distraction was started at the fifth postoperative day with a distraction rate of 0.5 mm twice a day. Twelve dogs were killed at the end of the distraction phase of 25 days (group A) and the remaining 12 dogs after an additional consolidation period of 25 days (group B). The tibia was removed from the distracted right leg and from the left control side of each animal, and longitudinal sections were cut and stained with Pentachrome. In all tibiae, an area of 0.5 x 2.4 cm within the endosteal bone was evaluated histomorphometrically with a Metz grid, and the results were compared between distraction and control side as well as between the dogs of group A and group B. Results: On the distraction side, the typical signs of an increased de novo bone formation with a significant increase of osteoblasts and osteoid in group A, as well as an additional significant increase of bone volume and trabecular thickness in group B, were found. In all distraction cases, islands of cartilage formation, which underwent enchondral ossification, were found, besides membranous ossification. The ratio between membranous and enchondral ossification was found to be five to one. Conclusion: Bone formation during distraction osteogenesis results from both membranous and enchondral ossification.