[Adaptive remodeling of bone--change of radius shape after resection of ulna in dog].

Bone changes its shape adaptively according to the mechanical environment, suggesting a close relationship between the bone remodeling and the stress induced in bones. We measured the geometries of the canine radius after partial resection of the ulna with X-ray CT and microscopic study with fluorescent labeling. The experimental animals were six beagle dogs aged three months. The midshaft of their right ulna was partially resected. The experimental period of them was 6, 12 and 24 weeks. Sectional images of their antebrachium were taken every 2 or 4 weeks with X-ray CT. The bone was labeled with Calcein and Xylenol Orange each week. From CT observation, significant bone growth was observed at cranial-lateral, caudal-medial side and resected ulnar side at 6 weeks after surgery. At 12 weeks, the thickness of cortical bone was increased. At 24 weeks, the cross-section changed to an oval or round shape. From confocal laser microscope observation, significant new bone formation was identified under the periosteum at the cranial-lateral and resected ulnar side from 2 weeks after surgery. On the control side, lamellar bone formation took place in an orderly manner, whereas on the experimental side, there was a large quantity of rapid woven bone formation filling the cavities of the resected ulna, followed by the lamellar bone formation. The bone formations took place to compensate for the mechanical functions of the lost ulna, suggesting the adaptive nature of bone remodeling.