Patellar luxation is often referred to as
“trick knee cap”
Small (toy) breed dogs, such as the Poodle,
Yorkshire Terrier and Chihuahua are most commonly affected
Larger breeds and cats are less commonly affected.
Most pets are born with the condition but
occasionally it is caused by trauma.
It typically results in intermittent hindleg
lameness which progresses slowly over months to years.
The knee joint (stifle) has a number of important
parts illustrated below:
The patella (knee cap) is found within the
patellar ligament which attaches femur muscles to the tibial tuberosity.
When properly aligned, as seen at left, the
patella tracks in the femoral groove and gives the knee stability and normal
When improperly aligned, as seen at right,
the patella “pops out” of the femoral groove.
Refers to the condition which occurs when
the knee cap “pops out” or dislocates out of the femoral groove.
Usually the result of misalignment of the
tibial tuberosity with the patellar groove at birth.
Occasionally, a traumatic event results in
luxation of the patella.
The patella can luxate toward the inside (more
common) or outside of the knee (less common).
As a result of luxation, the femoral groove
becomes shallow and narrow.
Knee instability, pain, lameness, joint swelling
and eventually arthritis result.
Some animals with patellar luxation also have
other knee abnormalities such as cranial cruciate ligament rupture.
Diagnosis is made by examination of the
knee joint and identifying patellar luxation. Sometimes sedation
or anesthesia is required to make a definitive diagnosis. Occasionally,
findings on X-Rays are utilized to support suspicion of patellar luxation
and to rule-out other causes of hind leg lameness.
Initial treatment is usually rest and
anti-inflammatory medications. Some small breed dogs do very well
with rest and anti-inflammatory medication. However, many small breed
dogs and most medium and large breed dogs require surgery to resolve lameness.
As a general rule, if a pet remains lame, or again becomes lame, after
2-4 weeks of initial treatment, surgery will eventually be necessary.
Surgical repair of Patellar Luxation
is described below.
Patellar Luxation Repair
Goals of Surgery:
Many dogs need surgical repair for resolution
A successful outcome with surgery is expected
in 90-95% of cases.
Even with surgery, some arthritis will develop
in the knee.
General anesthesia is utilized for the procedure
The faint scar remaining after surgery usually
becomes covered with fur again.
An overnight stay is required so discomfort
can be controlled with injectable pain medication.
Relieve pain associated with the patellar
Prevent damage to ligaments and cartilage
within the knee.
Decrease the amount of arthritis which will
inevitably develop in the knee.
Limit stress put on the opposite limb and
other limbs and joints.
Repair of patellar luxation involves three
Exploration of the knee joint to identify
any ligament or cartilage damage.
Realignment of the tibial tuberosity
with the femoral groove.
Formation of a normal femoral groove
by deepening and widening it.
The recuperative period typically lasts for
a total of 8-12 weeks.
Pets gradually begin to put weight on the
operated leg over the first 14 days.
Physical therapy comes in the form of progressively
longer leash walks over the following weeks.
Outcomes, Complications, and Risks:
Initially, exercise is limited to walks to
Skin sutures are removed 10-14 days after
Exercise on leash is gradually increased over
the following weeks; swimming is also excellent exercise.
Pain medication and antibiotics are administered
for several days after surgery.
No running, jumping or playing is permitted
for at least 8 weeks following surgery.
Cost of the Procedure:
Most pets are permitted to resume normal activity
several months after surgery.
5-10% of dogs have lameness after surgery
which is controlled with medication.
Occasionally, pins placed as part of the realignment
procedure need to be removed.
Rarely, infection after surgery makes additional
Cost for surgery is dependent on pet weight
and typically includes examination, pre-anesthetic bloodwork, anesthesia,
surgery, hospital care, post-operative medications, and two follow-up examinations.
Please ask your veterinarian for a detailed
surgical estimate for your pet.