Diagnosis:  Congenital/Traumatic Patellar Luxation

Miniature toy breed dogs are predisposes to medial patellar luxation.  The 
pathophysiology of this condition can stem from a congenital or a traumatic origin.  In 
our case since the dog did face a traumatic incident within the past year we feel that the 
patient had a congenital weakness that was aggravated by trauma and these two factors 
contributed to medial patellar luxation of the right stifle.      

When the patient fell a year ago the right stifle joint was stressed.  The joint capsule, 
patellar ligament and the lateral collateral ligament were over-extended during the 
traumatic incident.  Due to the compromise of these ligaments and the joint capsule the 
joint became unstable.  The instability in the joint permitted the stifle to rotate.  In 
addition the fact that the radiographs show a shallow  trochlear groove (congenital 
abnormality) all so predisposed the patient to patellar luxation .  The fact that we see mild 
torsional abnormalities in the femur indicate that this is more than likely an intermittent 
rather than permanent luxation.