Slipping Kneecap (Luxating Patella)
The patella, or kneecap, is a small bone that protects the front of the stifle joint on the rear leg. The patella is anchored in place by ligaments and slides in a groove in the femur called the trochlea. If the groove is too shallow, the patella will slip out when the knee bends.
Typically, a small dog will run, then hesitate and almost skin, then limp, and then try to stretch the leg backward to relieve the pain. With small dogs, the problem may come and go as the kneecap slips in and out of position.
Larger dogs are not as prone to slipped kneecaps. Instead, they generally have a sudden onset of lameness, which may actually indicate a torn cruciate ligament. The ligaments form an x inside the knee joint and connect to the femur (thighbone) with the tibia(the bone below the knee).
When the patella slips out to the inside of the knee joint, it is called a medial luxation. When it slips out to the outside, it is called lateral luxation.
Medial luxation is more common. It occurs in toy, miniature, and large breeds, and is apparent in some puppies when they begin to walk. It may appear later in others. The patella may slip in and out of place, resulting in a gait that is randomly abnormal. When the patella is out of place, the affected leg is usually carried with the leg bent and the foot turned inward. The conditional is bilateral (both sides) in 25% of cases.
Lateral luxation occurs in large and giant breeds at 5 - 6 months of age. A knock kneed stance is the most notable sign. The foot often twists outward as weight is placed on the limb. Both knees are almost always involved.
Luxating patella is usually an inherited developmental defect. Toy dog breeds often have problems with the kneecap slipping out of place due to the way their legs are designed. Rarely, it is acquired through trauma.
The diagnosis is made by attempting to push the patella out of the trochlear groove. The degree of luxation (movement) is graded 1 - 4, depending on how easy it is to dislocate the patella and whether the patella returns spontaneously to the trochlear groove. This manipulation should only be done by breeders or veterinarians experienced in this technique. Preliminary veterinary screening for medial patella luxation should be done on dogs of toy and small breeds at 6 - 8 weeks of age, before the pups are sent to their new homes.
- Pop the knee in - Dogs can usually pop the knee back into position if it slips out of place, but sometimes it locks. This is painful, and it prevents normal flexing of the joint. If this happens, you must help return the kneecap to the normal position.
It is best to have a second person help relax your dog while you treat the knee. The other person should hold your pet gently but with firm restraint by putting one arm around his neck and the other around his chest. If your dog is in pain or seems agitated, you may want to muzzle him as well. Loop pantyhose or a standard flat leash around his snout and knot it on top. bring the ends under his jaw and tie them again, then tie them behind his head.
to reposition the kneecap, slowly extend the leg straight out, place your fingers on the kneecap, and push it back into place. If your pet has any swelling or pain after you have popped the kneecap back into place, contact your vet.
The OFA maintains a patellar luxation registry and issues certificates to all dogs who palpatate normal at 12 months of age or older. Dogs with genetically determined patella luxation should not be bred.
Please contact your veterinarian for more information regarding this condition.
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