The most likely cause of lameness due to joint laxity in this case is a medial luxating patella.  The finding 
on physical exam that the patella is able to be moved out of the trochlear notch when the right hind leg is 
flexed and pops back on extension places this in a grade II/IV.  Small toy breeds like Pomeranians are 
genetically susceptible to this malformation.  It can be caused by a reduced coxofemoral angle, lateral 
bowing of the femur, internal rotation of the tibia, shallow trochlear groove, hypoplasia of the medial 
femoral condyle, or medial dysplasia of the quadriceps muscle mass.   The luxated patella causes a skipping 
gait as the patella pops in and out of place on flexion and extension.  The pain seen could be due solely to 
degenerative changes in the joint from the instability caused by the deformity, or due to secondary factors 
that increase the joint instability such as a torn cranial cruciate ligament or torn/displaced medial meniscus.  
Lack of cranial drawer in the awake patient does not rule out cruciate tear.  These inuries would probably be caused by trauma and will be further explored under hypothesis 2.  The unstable joint has friction 
in places not designed to handle it and as a result begins to break down.  As articular cartilage is lost from 
the joint surfaces increased pressure is placed in focal areas in the joint leading to increased breakdown of 
subchondral bone.  The movement of the patella back and forth in this case could also cause pain since the 
bones are not designed to move in this fashion.  The back of the patella could become rough and not glide 
easily in the trochlear notch causing abnormal friction and pain as the abnormal friction breaks the joint 
down.  Inflammation in the area can further lower the threshold for painful stimuli and cause an increased 
amount of pain to be felt by the patient.  A luxating patella can be caused by trauma or present 
congenitally.  In the case of trauma the pain would be from the damaged joint capsule.