Metabolic and histologic effects of recombinant canine somatotropin on bone healing in dogs, using an unstable ostectomy gap model

Objective - To investigate the effect of recombinant canine somatotropin (STH) on the metabolic and histologic aspects of bone healing in dogs, using an unstable ostectomy gap model. Animals - 8 mature dogs. Procedure - A 3-mm ostectomy of the mid portion of the radius was performed in all dogs. Implants designed to release STH at a rate of 4 mg/d were placed SC in 4 dogs (treated group [STHG]), and another 4 dogs received no implants (control group [CG]). Serum concentrations of STH, insulin-like growth factor I, and osteocalcin were determined before surgery, and weekly for 8 weeks. Scintigraphic evaluation of the ostectomy sites was performed before surgery, and at weeks 2, 4, 6, and 8 after surgery. Histologic evaluation of the ostectomy sites was performed at the conclusion of the study at week 8. Results - Significant (P < 0.05) increases in serum STH, insulin-like growth factor I, and osteocalcin concentrations were observed in dogs of the STHG during the 8-week study period. Scintigraphic activity of the ostectomy sites was increased in dogs of both groups, but dogs of the STHG had significantly (P < 0.05) greater activity, compared with dogs of the CG. Coalescence of nuclear activity across the ostectomy site was observed in dogs of the STHG, whereas dogs of the CG maintained 2 distinct areas of metabolic activity. Histologically, dogs of the STHG had bridging calluses with areas of endochondral ossification and ongoing osteogenic activity, whereas dogs of the CG had nonossified fibrocartilage typical of nonunion fractures. Conclusion - Using the ostectomy gap model, recombinant canine STH enhanced the metabolic and histologic aspects of bone healing in dogs.