[Partial resection of the ulna as a diaphyseal bone defect model in the dog]

A 25-mm periosteal cylinder was removed from the middle of the ulna in fully grown mongrel dogs. A silastic block was interposed and the defect was fixed by a plate. Eight weeks later, the block was removed. During the following 24 weeks, spontaneous bone regeneration was evaluated by radiologic and histomorphometric evidence. In a second series, three screws were placed transversely to the longitudinal axis from the ulna into the radius to stabilize the partial resected ulna. The observation period after silastic removal was 16 weeks. Evaluation was based on radiology and on Indian ink stain of the vessels. Plate fixation provides an essentially stable defect model, with partly considerable bone apposition to the proximal area of resection. This is explained by the entry of the only nutrient artery into the proximal diaphyseal third. No instance of spontaneous defect healing following plate fixation was observed. The transverse fixation of the ulna revealed early radiologic signs of instability.