Client Education

Medial Luxation of Right Patella

Titan has a fairly common condition we see in a 
variety of small breed dogs, 
like Pomeranians.  The 
extensor mechanism (the anatomic features that 
allow muscle contraction to 
extend the dogŐs knee joint) of 
the stifle joint is abnormal.  Consequently, 
abnormal forces generated during 
movement of the joint allow 
the dogŐs patella (kneecap) to dislocate medially 
(inwards towards the dogs 
body).  This luxation of the 
patella can inhibit normal movement of the joint 
and affect the animalŐs gait.  
To walk normally again, the 
patella must pop back into place.  This extensor 
mechanism is composed of the 
quadriceps muscle group, 
the patella, trochlear groove of the femur, 
straight patellar ligament, and the 
tibial tuberosity.  A normal 
stifle maintains a straight line through this 
extensor mechanism for normal 
motion.  A variety of 
musculoskeletal abnormalities, either present 
congenitally or acquired through 
trauma, can disrupt the 
straight line and upset normal motion of the 
stifle.  TitanŐs radiographs were 
normal.  We saw no bony 
changes or abnormalities.  Consequently, we might 
suspect a soft tissue problem, 
possibly a congenital medial 
displacement of the quadriceps or injury to this 
muscle that caused scarring and 
contracture.  Trauma could also have caused injury 
to TitanŐs joint capasule, 
which could compromise the normal support to the 
joint.  This could 
disrupt the straight line of the extensor mechanism 
and cause the patella to be 
pulled medially out of the 
trochlear groove when the stifle is extended and 
the ligaments arenŐt taunt.  We 
grade patellar luxations, 
and TitanŐs is relatively mild, a Grade I-II.  The 
patella luxated when we 
extended the dogŐs leg and put 
pressure on it with our thumb.  Normally, we just 
monitor Grade I luxations 
since minimal clinical signs 
are associated with the disorder.  In order to 
treat clinical lameness, 
we recommend surgery to stabilize the dogŐs 
patella.  Exercise will need to be restricted 10-12 
weeks post-operatively.  Titan will be able to use 
the leg almost immediately, however, a gradual 
return to full joint motion is to be expected.