Diagnosis:

Fracture of Left femur, right tibia and fibula

     The automobile hitting the dog created a large force that was absorbed by a 
large area of the dog's body.  The more flexible structures were able to give 
way somewhat with the force, but the force was large enough to damage some 
structures leading to the hemorrhage seen.  The force was greater than the 
elastic force of the rigid components, like the bones.  The bones absorbed the 
force through breaking.
     
     The fragments of bone should heal after they are realigned.  The first 
phase of healing is inflammation which the bone ends will be undergoing as soon 
as they are positioned.  As the vessels surrounding the area bleed the clot 
collects as a hematoma which is the first connection between the bone ends.  
This serves as a support for fibroblasts to migrate onto.  There is an increased 
blood supply from the surrounding tissues until the normal vasculature can be 
reestablished in the area.  The fibroblasts lay down fibrous tissue where the 
hematoma is formed.  Then that is replaced by cartilage followed by immature 
bone.  The bone is remodeled to be more like normal bone.  The better the bone 
is aligned the faster they will heal.  Bone can also fill in gaps if necessary, 
but this takes longer and the bones should be aligned if possible.