Diagnosis

	The diagnosis is hypertrophic viable delayed union of the third and fourth 
metacarpal of the left front leg.  Unfortunately, the original cast placed on the leg did not 
align the fragments of the bone properly, resulting in the valgus deformity seen on physical 
exam. The instability of the cast, the large fracture gaps, and the localized infection all 
support that the valgus deformity is a result of the fracture and not a congenital deformity.  
However, to confirm that the valgus deformity is not congenital, we recommend taking an 
anterior/posterior radiograph before continuing with treatment.  Assuming that the fracture 
caused the valgus deformity, we would expect the fracture to be the only deformity on the 
radiograph and normal conformation of the proximal and distal ends of the metacarpus.
	There is a good blood supply to the fracture site as evidenced by the hypertrophy 
seen.  In fractures with a good blood supply and some movement, pleuropotential cells 
become fibroblasts which results in fibrous tissue formation between the bone fragments.  
This fibrous tissue must then mineralize and ossify.  This process is slow as the 
mineralization is ossified by creeping substitution.  
We are concerned about the quality of the blood supply to the distal portion of the 
fracture, as the hypertrophy is not as great as in the proximal fracture.  If, in fact, the blood 
supply is poorer, it is likely that the pleuropotential cells become chondroblasts.  The 
ossification of the cartilage would then occur by enchondral ossification.