Hypothesis 2: 

Congenital Abnormalities 

Predisposing to patellar luxation, trauma and/or degenerative changes.  We chose 
this 
hypothesis because of the breed.  Pomeranians are predisposed to congenital 
abnormalities of the stifle joint. 

There are a number of possible congenital abnormalities that can cause problems 
in the 
stifle joints.  We suspect from our physical exam that both stifles are affected 
which 
supports our congenital abnormality hypothesis.  We are focusing on the medial 
luxation 
of the patella found on physical exam in this hypothesis.  We are hypothesizing 
that this 
luxation could cause the joint to be instable and predispose the dog to injury 
when it fell 
off the bed and possible degenerative changes.

1. Shallow trochlear notch can cause poor articulation of patella and femur.  
This causes 
instability in the stifle joint, allowing patella to luxate freely.  
2. Misalignment of muscle groups involving the joint, especially quadriceps.  
The 
quadriceps could be attached medial to the midline of the patella, pulling the 
patella 
medially upon extension.
3. Medial condyle of femur develops improperly, allowing the patella to slide 
medially.