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Name
Patellar Luxation, Medial and Lateral, Canine
Short Description
Medial and lateral patellar luxation
Affected Animals: Dogs, cats, humans
Overview: Patellar luxation is usually a congenital
condition in which the kneecap, or patella, dislocates outside of
its normal trochlear groove. Dislocation, clinically referred to as
luxation, can occur on either the medial, or inside surface, or the
lateral, or outside surface, of the knee. There are varying degrees
of patellar luxation that are graded depending on whether the
patella is intermittently or constantly luxated. This abnormal
displacement of the kneecap results in pain, cartilage damage, and
arthritis. There are varying degrees of severity of this disease,
and surgery may be needed.
It is much more common for the kneecap to ride on the inside than on
the outside surface of the knee. This condition typically affects
small and miniature breeds such as the poodle, Pomeranian,
Chihuahua, Schipperke, Bichon Frise, and pug. It is also seen in the
cocker spaniel, golden retriever, Labrador retriever, and mixed
breeds.
Patella
Femur
Patellar ligament
Tibial Tuberosity
Medial Luxation of Patella
Lateral Luxation of Patella
Outside dislocation of the kneecap, or lateral patellar luxation,
occurs more often in large breeds such as the Great Dane, Saint
Bernard, and Bernese mountain dog. Lateral luxation is often
accompanied by malformation of the femur, the large bone in the
thigh. In these cases the prognosis is more uncertain, as major limb
reconstructive surgery may be needed.
Generally, the prognosis is better when corrective surgery is
performed early in the course of the disease; many of the
malformations in the bones and joint occur over time and can be
prevented with early correction.
Clinical Signs: Lameness that is often intermittent, and may be
unilateral or bilateral; thick, swollen stifles; pain on
range-of-motion; crepitus; palpable luxation; inability to jump or
walk normally; medial displacement of quadriceps muscle group;
lateral bowing of the distal third of the femur.
Symptoms: Intermittent or consistent lameness; bowlegged
stance; reluctance to walk or jump; occasionally holding a rear leg
out to the side when walking.
Description: Medial patellar luxation, or MPL, is a very
common disease of small and miniature breeds in which the kneecap
occasionally rides on the inside of its normal groove. Primarily
congenital, although occasionally acquired through trauma, MPL
causes lameness in one or both rear limbs. The degree of lameness is
determined by the severity and duration of the disease, as well as
the extent of existing arthritis.
Patellar luxation is graded on a scale from I to IV, with IV being
the most severe. The disease can progress from the less severe to
more severe grades over time. The more severe forms are often
accompanied by malformation of the femur and tibia, as well as
varying amounts of arthritis.
Dogs are frequently presented to a veterinarian for intermittent
lameness, often because it is becoming more frequent or severe. When
the patella, or kneecap, pops out of its normal trochlear groove,
the dog feels pain, and owners may report a hitch in the gait. The
dog will frequently extend the knee out from the body in order to
get the patella to pop back in to the trochlear groove. As MPL
progresses, the structures that hold the patella in place become
looser, and thus the problem becomes more frequent. This dislocation
causes pain, and as the frequency increases, so does the lameness.
Unfortunately, many of the severe Grade III or IV
cases go unnoticed for months or years because the affected animals
are usually miniature breeds that are often carried much of the time
by their owners. Their inability to jump or straighten out their
hind legs may go unnoticed because of their small size and sedentary
lifestyle.
Lateral patellar luxation, or LPL, is less common than MPL and
occurs when the kneecap occasionally rides on the outside of its
normal groove. It, too, can be congenital or acquired, with the
congenital form again being more common. While it can occur in any
dog, it is more common in large and giant breeds. LPL is frequently
accompanied by malformation of the femur and/or tibia. The disease
can produce marked lameness and progress to crippling arthritis.
Because of the accompanying bony malformations, extensive surgery
may be required to correct this problem.
Diagnosis: The examining veterinarian will often make a
diagnosis from a physical examination and history. However, x-rays
are needed to determine the degree of arthritis, and evaluate for
any malformation of the femur and tibia, the two major bones in the
leg, which are joined together at the knee.
Prognosis: The prognosis for a Grade I patellar luxation is
very good. These dogs may not need surgery. However close
observation for signs of worsening is important. If surgery is
indicated and performed early on, most animals regain normal
functionality.
The prognosis for Grades II and III depends on how much arthritis
and malformation have occurred. If caught and treated early, both
have a good to excellent prognosis. If there is significant bony
malformation or arthritis, the prognosis is guarded to fair.
The prognosis for Grade IV patellar luxation is guarded. Most of
these animals have moderate to severe bony malformations and
significant arthritis. If correction is performed, it is important
to initiate early physical therapy to help restore function.
Transmission or Cause: The congenital condition is probably genetic in
nature, and as such, affected animals should not be bred. Trauma or
injury can also cause patella luxation.
Treatment: Treatment involves replacing the kneecap into the
groove, and preventing it from popping in and out. The following
procedures can be used alone or in combination as necessary to
maintain the proper function of the knee.
Imbrication Tightening the joint capsule, known as
imbrication, is done on the opposite side of the luxation to prevent
the kneecap from having enough slack to pop out of the trochlear
groove. Thus a medial patellar luxation is treated with a lateral
imbrication, and vice-versa. Additionally, the joint capsule can be
loosened on the side of the luxation; this is called a release
incision. This procedure relieves the tension that the joint capsule
is placing on the patella, thus allowing it to ride in the trochlea. In severe cases a synthetic suture is sometimes
necessary to keep the kneecap in place. This suture is placed on the
side opposite the luxation, and goes from behind the femur to the
patellar tendon. It also prevents the kneecap from popping over to
the other side.
Trochleoplasty Deepening of the trochlear groove, or
trochleoplasty, can be accomplished with a variety of techniques. A
chondroplasty technique involves cutting out a taco-shaped wedge of
cartilage, removing a small portion of bone beneath it, and then
replacing the cartilage. The result is a deeper groove. This
procedure can only be performed on very young dogs, because their
cartilage is thicker.
Trochlear recession involves cutting out the
cartilage and bone in such a way as to create a deeper trough. This
trough will then fill in with scar tissue over time. Because this
scar tissue is not as good as cartilage for joint function, this
technique has given way to others that attempt to preserve normal
cartilage. It can, however, be useful in carefully selected cases.
Wedge recession creates a taco-shaped piece of cartilage and
underlying bone. Then, the bone below the wedge is removed and the
wedge is replaced, forming a deeper groove. Block recession is
identical in principle to wedge recession, except that a rectangular
piece of cartilage and bone, rather than a wedge, is removed.
Tibial Tuberosity Transposition The kneecap attaches to the lower leg via its
patellar tendon at a bony site called the tibial tuberosity. Many
times this site forms abnormally on the inside, as with MPL, or on
the outside, as with LPL. In this procedure, the surgeon moves the
tibial tuberosity back into proper alignment and secures it in place
with a pin or wire. Realigning the joint, kneecap, and tendon
prevents dislocation from reoccurring.
Osteotomy In severe cases, with malformation of the tibia
or femur, corrective bone cuts known as osteotomies may be required.
