Diagnosis

This calf had a viable delayed union.  It is hypertrophic because there is a large callus formed at the proximal fracture end.  Delayed union is common in large animals because of their size and weight.  Rigid stabilization is difficult to provide even with internal or external fixation.  This instability, along with the large fracture gap, is a factor that has led to the delayed union.  Because open wounds are present, this fracture is considered open.  This local infection will cause further compromise to the healing of the fracture.  
	Ideally, the fracture would have begun repair with the help of rigid fixation, a good blood supply, and no infection.  A good blood supply with some movement at the fracture site will encourage fibroblast formation from the pleuropotential cells.  The fibroblasts will begin fibrous tissue formation at the fracture ends.  This tissue is then destroyed and replaced by dystrophic, calcified tissue.  This is then slowly ossified.  
	The open wounds are infected with Staphylococcus aureus and Escherichia coli.  These are localized infections that have not gained access to the rest of the body.