Hypothesis 2: Both legs are fractured from the trauma and additionally soft tissue damage is significant enough to cause abnormal movement in the left limb.

Instability of the right tibia leads us to believe that bone may have been fractured by the 
accident. 
Abnormal movement of limb, crepitation and extreme swelling of left hind limb led us to 
believe that a bone in the upper left hind leg is fractured.  Since this could not be 
localized by our initial orthopedic exam, we hypothesize that it could either be the upper 
femur, the hip joint itself or the pelvis.  Since the upper femur is at the level of a bumper 
of a car, it is a common bone broken when the dog is hit.  Within the hind limbs there are a variety of soft tissue structures that could be affected including major muscle groups..quadriceps, hamstrings, etc., ligaments and tendous structures. All of these stabilize the joint and disruption may cause abnormal movement in the left limb.  Soft tissue damage also would add to the significant swelling in the limb.