The patella (knee cap) is a movable bone located over the knee that connects the muscles of the
thigh to the lower leg. When the patella functions correctly, the dog can use the leg well. Patellar
luxation is a dislocation of the kneecap most often seen in small dogs. Most of these animals are
born with this problem and usually both knees are affected. A fall or twisting injury may
aggravate the already existing condition. A common symptom of this “trick knee” condition is a
dog that occasionally holds the leg while running but spontaneously starts using it again. This
happens as the kneecap pops in and out of place. Often the dog will give out a short cry or yelp
when this happens.
We classify luxating patellas depending on the severity. A Grade I is when the kneecap is mostly
in place and pops out on occasion. As the ridge wears down, the kneecap starts moving in and
out of place more often and is now a Grade II. When the cap is out of place more than in place, it
becomes a Grade III. And finally, when the cap is out all of the time, the knee is classified as a
Surgery is usually recommended if your pet is in a great deal of discomfort a lot of the time.
Several different types of surgery have been developed and your doctor will describe the one he
or she feels will help your pet. Remember, even if your pet does not appear to be in pain,
luxations make them more prone to rupturing their cruciate ligaments inside the knee later
in life due to the abnormal strain placed on them with this condition. This can lead to a
more expensive surgery and causes lifelong arthrtitis to develop within the knee joint. If the
end of the femur is starting to “bend” in very young patients, surgery should be done
immediately, otherwise it should be done around six to eight months of age when growth is
complete and healing is fast compared to older patients..
What Options are Available for Treating Patellar Luxation?
Patellar luxations that do not cause any clinical sign should be monitored but do not typically
warrant surgical correction, especially in small dogs. Surgery is considered in Grades II and over
(See above). One or several of the following strategies may be required to correct patella
Reconstruction of soft tissues surrounding the knee cap to loosen the side toward which
the patella is riding and tighten the opposite side
Deepening of the femoral groove so that the knee cap can seat deeply in its normal
Transposing the tibial crest, bony prominence onto which the tendon of the patella
attaches below the knee. This will help realign the quadriceps, the patella and its tendon.
Correction of abnormally shaped femurs is occasionally required in cases where the knee
cap rides outside of its groove most or all the time. This procedure involves cutting the
bone, correcting its deformation and immobilizing it with a bone plate.
The procedures that will best address the problem are selected on an individual basis by the
surgeon that has examined the patient. Since there is a genetic predisposition to this condition, pets that have patella luxations that are not due to trauma should not be bred.