Medial patellar (kneecap) luxation may be
congenital (present at birth) or acquired.
The congenital form is most common in toy
and miniature breeds such as Miniature Poodle,
Yorkshire Terrier, Toy Poodle, Chihuahua,
Pomeranian, and Pekingese and may occur
simultaneously with other pelvic limb deformities.
While the definitive sequence of events which leads
to these deformities has not yet been established,
the age at which the syndrome occurs does play
an important role in the severity of the degenerative
changes in the joint.
When patellar luxations are present early in life,
the major muscle groups of the thigh pull toward
the inside of the leg, putting abnormal pressure on
the knee joint cartilage. The result is a bowlegged
stance and an abnormal pull on the patella
(see illustrations below). Thus, a number of
anatomic pelvic limb deformities can result from
the structural manifestation of medial patellar
luxation. These include bowed legs,
coxofemoral (hip) joint abnormalities, and outward rotation of the limb.
When the patella is in its normal position, its cartilage surface glides smoothly
and painlessly along the cartilage surface of the trochlear groove with little or no
discomfort. As the patella pops out of its groove, these cartilage surfaces rub
each other. The animal may cry and try to straighten the leg to pop the patella
back into position or may hold the limb up until muscle relaxation allows the
kneecap to reposition itself. This resembles an intermittent lameness. There is
little or no discomfort until the cartilage is eroded to a point where bone touches
bone. From this point on, each time the patella pops out into its abnormal,
luxated position, it will cause pain. This explains why many dogs have no
clinical lameness until they reach adulthood when progressive cartilage wear
creates an acutely painful condition.
Because there is great individual variation in the pathologic deformities seen, a
graded classification of medial patellar luxation (Putnam 1968) has been
formulated as a basis for recommending which type of surgical repair is most
appropriate for each individual. In the following description each classification
is addressed:
GRADE I
The anatomic alignment of the stifle is normal with the patella luxating only
when pushed out of the socket.
GRADE II
The patella luxates upon flexion of the joint and remains luxated until returned
by manual pressure.
GRADE III
The patella is permanently dislocated but can be reduced manually with the limb
extended.
GRADE IV
The patella is permanently dislocated and cannot be manually reduced.
Treatment
The procedures for repair of medial patellar luxation deal with repositioning and
stabilizing the kneecap in the patellar groove of the femur. Depending on the
severity of the deformities, the technique may be as simple as soft tissue
reconstruction or as complicated as multiple corrective osteotomies
(straightening the bone).
The most commonly accepted surgical procedures include:
* Deepening the trochlear groove.
* Tightening the tissues around the joint.
* De-rotating the femur or tibia.
* Repositioning the patellar ligament attachment to the tibia.
Postoperative Care
After surgery is completed, the affected leg(s) will be bandaged for three to six
weeks. Passive physical therapy is begun immediately after bandage removal to
work out the stiffness and reestablish a normal range of motion in the joint.
During the next three to four weeks, light walking around the house or
supervised short walks outside must be strictly controlled until a progressive
building of muscular support and stamina leads to unrestricted normal function.
Please visit our page on post-op MPL care for more information
Medial Patella Luxation
