Hypothesis #1  -- Trauma

     The initial injury resulting from the fall could have ruptured the medial collateral 
ligament of the stifle joint, resulting in the RR lameness and patellar luxation. Subsequent 
fibrosis of rupture allowed clinically normal signs of 5 months duration; wear and tear to 
the fibrosed ligament lead to recurring lameness.

     Initial injury could have been fracture to the distal femur (trochlear ridge). Without 
veterinary intervention, the bone healed abnormally, resulting in disproportionate joint 
configuration and articular cartilage damage. The abnormal joint alignment weakened the 
supportive structures of the joint, and allowed patellar luxation and disproportionate weight 
bearing. 

     The absence of pain sensation in the RR limb post trauma, suggests possible nerve 
involvement around the stifle joint capsule. Ligament damage and subsequent repair could 
have compromised nociception to the joint; the presence of pain on the left hind rules out 
spinal cord damage. 

      Muscle damage from initial trauma may have repaired abnormally and disrupted normal 
joint kinetics, fibrotic scarring and muscle contracture could lead to abnormal weight 
bearing, patellar luxation, and progressive joint disease.