WHAT CAUSES THIS TO OCCUR?
The
muscles of the thigh attach directly or indirectly to the top of the
knee-cap. There is a ligament, called the patellar ligament, which
runs from the bottom of the knee-cap to a point on the tibia (shin
bone) just below the knee joint. When the thigh muscles contract,
the force is transmitted through the patella and through the
patellar ligament and results in extension (straightening) of the
knee joint. The patella stays in the centre of the leg because the
point of attachment of the patellar ligament is on the midline and
because the patella slides in a groove on the lower end of the femur
(the thigh bone).
The patella luxates because the point of attachment of the patellar
ligament is not on the midline of the tibia. It is almost always
located too far medial (toward the middle of the body). As the thigh
muscles contract, the force is pulled against the groove on the
inner side of the femur. After several months or years of this
abnormal movement, the inner side of the groove wears down and the
patella is free to move out of the groove or dislocate. When this
occurs, the dog has difficulty bearing weight on the leg. It may
learn how to kick the leg and snap the patella back into its normal
location. However, because the side of the groove is gone, it
dislocates again easily.
DOES
A LUXATING PATELLA CAUSE ANY LONG-TERM PROBLEMS FOR MY DOG?
Some
dogs can tolerate this problem for many years, some for all of their
lives. Since the joint surfaces are very slick and bathed in a
slippery joint fluid, there is usually little or no discomfort early
in the process. However, this abnormality predisposes the knee to
other injuries, especially torn cruciate ligaments. Also, with
advancing age, the joint may become arthritic and painful. The bones
may actually curve in response to the abnormal location of the
kneecap..
CAN A LUXATING PATELLA BE
CORRECTED?
Surgery
should be performed if your dog has a persistent lameness or if
other knee injuries occur secondary to the luxation.
The methods used for surgical repair depend on how far the process
has gone before intervention. Surgical repair may include any or all
of the following:
1) The point of attachment of the patellar ligament is cut from the
tibia and transplanted to its proper location to correct the in
correct alignment.
2) The groove in the femur is deepened so the patella will stay in
place.
3) The capsule around the joint is tightened. This last step is
important because the joint capsule will have stretched during the
period of luxation. If the surgery is performed before arthritis
occurs, the prognosis is excellent. Your dog should regain full use
of its leg. However, if arthritis has already occurred, the joint
will still be somewhat painful, especially in cold weather.
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