Issue Description Is a condition in which the patella, or
kneecap, dislocates or moves out of its normal location. Other Names Luxating Patella, Trick Knee, Subluxation of Patella
Symptoms Most cases of patellar luxation are medial and
this is frequently a congenital problem in toy and miniature breed
dogs. Breeds showing a predisposition for medial patellar luxation
include miniature and toy poodles, Yorkshire terriers, Pomeranians,
Pekingese, Chihuahuas and Boston Terriers. Large breed dogs are also
affected and the Labrador retriever seems particularly
predisposed.Patellar luxation is less common in cats than in dogs.
Predisposed breeds include the Devon Rex and the Abyssinian. Although
the specific cause of patellar luxation is unknown in these cases, it
is generally agreed that a defect in hind limb conformation is the
It can be caused by some form of blunt
trauma, or may be a congenital defect. In congenital cases, it is
Diagnosis Diagnosis is made through palpation of the
knee. X-rays are necessary in some cases. The luxating patella often
causes no or very slight symptoms. There may be intermittent limping
in the rear leg. Osteoarthritis can develop secondarily.
There are four diagnostic grades of patellar luxation, each more
severe than the previous:
Grade I - the patella can be
manually luxated but is reduced (returns to the normal position) when
Grade II - the patella can be manually luxated or it can
spontaneously luxate with flexion of the stifle joint. The patella
remains luxated until it is manually reduced or when the animal
extends the joint and derotates the tibia in the opposite direction of
Grade III - the patella remains luxated most of the time but can
be manually reduced with the stifle joint in extension. Flexion and
extension of the stifle results in reluxation of the patella;
Grade IV - the patella is permanently luxated and cannot be
manually repositioned. There may be up to 90¼ of rotation of the
proximal tibial plateau. The femoral trochlear groove is shallow or
absent, and there is displacement of the quadriceps muscle group in
the direction of luxation.
Treatment Grades III and IV, as well as some grade II
cases, require surgery to correct, if the animal has difficulty
walking. The surgery involves a sulcoplasty, a deepening of the
trochlear sulcus that the patella sits in.
can be given with the use of pet ramps, stairs, or steps. These can
help the animal travel from one place to another, especially up and
down, without adding any pain or damage to the patella.