Luxating patella is a condition in which the patella (kneecap) moves sideways out of its groove due to trauma or malformation of the ridges of the groove. The result is that a dog's joint "locks" in a bent position. Usually when this occurs, the patella cannot move back into normal position until the quadriceps muscle has relaxed. As long as the muscles are contracted the joint is forced to stay in a flexed position.
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Causes
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Patellar luxation may be caused by a traumatic injury or a development of cranial cruciate deficiency. In most cases, however, the cause is unknown, according to the American College of Veterinary Surgeons. A congenital misalignment can result in patellar luxation along with other problems such as hip dysplasia, malformation of the tibia or femur, and tightness of the quadriceps.
Signs/Symptoms
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Symptoms of patellar luxation include sudden pain and lameness when running. Pet Education indicates that in most cases it occurs in the rear legs of middle-age dogs. Frequently the dog will hold its leg up for a few steps before recovering full use of it. At times the dog will shake or extend the leg before using it again. According to the American College of Veterinary Surgeons, the lameness increases in frequency as the condition progresses. Young puppies with the disease will have a bow-legged look in their rear legs.
Diagnosis
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The American College of Veterinary Surgeons indicates that diagnosis of patellar luxation is made by physical examination and palpation of the knee, X-rays of the knees, pelvis and tibias, and CT scans of the rear legs. In cases where patellar luxation is diagnosed but does not cause any symptoms, the condition needs to be monitored.
Treatment
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In most cases, surgical correction is necessary to prevent progressively worsening lameness. It can eventually result in premature arthritis, deformation of the leg, and continued pain. Several surgical procedures that may be used include reconstruction of the tissues that surround the kneecap, increasing the depth of the femoral groove for better containment of the kneecap, and movement of the tibial crest to realign the patella, its tendon and the quadriceps. Surgical procedures for large dogs are often difficult, particularly when a dog has other conditions, such as hip dysplasia or cranial cruciate disease.
Risk Factors
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Small dog breeds are more prone to patella luxation, particularly toy and miniature poodles, according to Pet Education. It also occurs in Chihuahuas, Yorkshire terriers and Pomeranians. Some breeds with short legs, such as the dachshund and basset hound, have the condition secondary to an abnormal shape of its legs.
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