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Patellar Luxation in Cavaliers: Genetic and Degenerative
The Cavalier as a breed suffers from a
recurring hereditary condition which causes luxating patellas. The disorder
is believed to affect 20% to 30% of Cavalier King Charles spaniels. The
patella is the knee cap of the Cavalier King Charles spaniel. It should be
located in its groove in the center of the stifle (knee joint) of the femur
(upper leg bone). A luxating patella is a knee cap that moves out of its
groove. Genetic conditions which cause patellar luxation are a shallow
groove, weak ligaments, and misalignment of the muscles and ligaments
between the femur, patella, and tibia (lower leg bone).
If the condition is not corrected, it will degenerate: the patella's ridges will wear, its groove will become shallower, and the Cavalier will become progressively more lame. Arthritis will prematurely affect the joint, causing a permanently swollen knee with poor mobility.
Symptoms & Diagnosis
Veterinarians can check for patellar luxation by manipulating it. The dog is examined awake and the veterinarian classifies its degree of luxation. Adult Cavaliers should be evaluated annually, and puppies should be examined at 6-8 weeks of age prior to their release to the new owners.
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There are four grades of severity of patellar luxation, and they usually progress Grade 1: The patella is nearly normal and can be only dislocated if the stifle (knee joint) is expanded and digital pressure is applied. Grade 2: The patella can be dislocated in extension and remains out of place when the stifle is flexed (Cavaliers with this condition may suffer from joint cartilage and secondary osteoarthritis due to the patella constantly dislocating). Luxation occurs when there is occasional spontaneous lameness, but the patella returns to normal positioning easily, and the dog usually does not indicate pain. This dog typically occasionally carries a rear leg for two or three steps but then puts it back down as if nothing was wrong. Grade 3: The patella is dislocated most of the time; it can be manually repositioned, but it slips out easily again (Cavaliers with this degree can also be a high risk for rupture of the anterior cruciate ligament in the knee joint). Luxation is to the extent that the dog begins to have a loss of function. It has more frequent "skipping" episodes and may not want to jump up; it may have pain, and the patella does not always return to normal positioning when it is pushed out of its groove during a physical exam. Grade 4: The patella is dislocated all of the time. The dog's legs are painful enough that it tries not to use them, when the leg can not be fully straightened manually, and the dog shows evidence of chronic pain or disability, including poor or no ability to jump up. |
Treatment
Veterinary orthopedic surgery usually is required to correct the condition, especially if Grade 3 or 4. The groove may be surgically deepened to better contain the patella. The patella itself may be tied down laterally (on its outside), to prevent it from deviating medially (toward the inside). The bony protuberance at the point the quadriceps tendon attaches to the tibia may be cut off and then re-attached in a more lateral position.
Breeders' Responsibilities
The Canine Inherited Disorders Database (www.upei.ca/~cidd/intro.htm) recommends that any dogs with patellar luxation not be bred, nor should their parents or littermates. Because of the strong hereditary relationship, all Cavalier King Charles spaniel breeding stock should be examined by qualified veterinarians at least annually and cleared for patellar luxation, the closer the examination to the breeding the better.
Related Links: Questions for Breeders
Veterinary Resources:
Control of Canine Genetic Diseases, Padgett, G.A., Howell Book House 1998, pp. 198-199, 246.
Guide to Congenital and Heritable Disorders in Dogs, Dodds WJ, Hall S, Inks K, A.V.A.R., Jan 2004, Section II(235).
Complications Associated with Corrective Surgery for Patellar Luxation in 109 Dogs. Gareth I. Arthurs and Sorrel J. Langley-Hobbs. Vet. Surg. Aug 2006; 35:559.
Patellar luxation. Greg Harasen. Can Vet J. 2006 August; 47(8): 817–818. Quote: "Congenital luxation of the patella represents one of the most common orthopedic conditions in small animal practice. Medial luxations account for 75% to 80% of cases in all breeds. The majority of patients are small breed dogs including ... cavalier King Charles spaniels. ... The overwhelming majority of patellar luxation are congenital and certainly hereditary, although a mode of inheritance has not been described."
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