Chihuahuas are feisty, intelligent little dogs that typically enjoy good health and long lives. However, like every breed, the Chihuahua has genetic predispositions for certain ailments and conditions. One of the most common problems found in Chihuahuas is patellar luxation (dislocated knee caps). Although luxating patellas can result from trauma, they are usually a congenital (from birth) or developmental condition. Fortunately, this condition is never life-threatening, and it's almost always correctable.
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What is Patella Luxation?
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In healthy canine knees, the knee cap glides between grooves at the bottom of the femur (thigh bone). However, if your Chihuahua has luxating patellas, the bony ridges that form the grooves are compressed, thus creating a groove that is too shallow for proper gliding. When your Chihuahua walks or runs, his knee cap may jump (luxate) sideways out of it's groove and over the bony ridge, causing the leg to lock up and producing a fair degree of pain. Usually, once your Chihuahua has relaxed his leg, his kneecap will return to its proper place, and he will proceed as if nothing happened.
Symptoms
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It is not difficult to spot a luxating patella in a Chihuahua. Depending on the severity of the luxation, he may limp. He may appear to engage in intermittent skipping when running, or he may not be able to place any weight at all on the affected leg. He may yelp if the pain is great. You may also hear a "cracking" noise when he moves, when you hold him up against yourself or place him in your lap.
Diagnosis
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Even if your Chihuahua's luxating patellas do not seem to bother him, it's a good idea to have them evaluated. Your veterinarian will test the range of motion in your Chihuahua's legs, noting the luxation of the knee caps throughout each point of motion. He will be able to actually pop the cap back and forth within the groove. He may also opt to take x-rays. The luxation will be graded on a scale of 1 to 4: typically, a grade 1 luxation will not require surgery, grade 2 is typically a "watch it and see" scenario, and grades 3 and 4 will benefit from surgical correction.
Treatment
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If your Chihuahua has a grade 1 or 2 luxation, then conservative management will be the first line of treatment. Your Chihuahua will be able to play and exercise normally, but you should not allow him to jump up or down from high places and rough play with other dogs should be monitored closely. If your Chihuahua has a grade 3 or 4 luxation, there are several surgical procedures available: lateral imbrication (adjusts the joint capsule to prevent luxation); trochlear modification (deepens the patellar groove); and tibial crest transposition (for the most severe cases where the leg bones have also rotated inward).
Prognosis
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It is not unusual for Chihuahuas with luxating patellas to live long, normal lives without ever needing any treatment. He'll likely just need a watchful owner and healthy food that provides plenty of joint-supporting nutrients. If your Chihuahua has had surgery to correct a grade 2 or 3 luxation, prognosis is generally very good. The prognosis following surgery for a grade 4 luxation is guarded, and it will depend on the severity of the deformity and if any further knee damage is incurred.
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