Toy breeds are very prone to lateral luxating patellas.
Patellar luxation is most common in Poodles, Yorkshire Terriers, Pomeranians, Pekingese, Chihuahuas, Miniature Pinschers and Boston Terriers. Females have the highest risk for this condition.
Diagnosis is relatively simple for a veterinarian familiar with orthopedics. It involves palpation of the joint and manual luxation of the patella. Care must be exercised with the examination to avoid injuring the joint, or making an incorrect diagnosis. Patellar luxation may be classified in four grades, with grade I being the mildest. This grading system is subjective so it is important in the present of luxation to have the same veterinarian perform the follow-up screening. Mild patellar luxation (grade 1-2) may be discovered as an incidental finding especially in a growing dog or a female in season. In addition, patellar luxation may occur in any breed because of trauma.
Patella luxation (also called slipped stifles) results from abnormalities in the bones of the rear legs, such as a shallow trochlear groove. This condition is easily checked by manipulation by a veterinarian. Patella luxation is graded into 4 degrees of severity.
The four degrees are:
Grade 1 - the stifle joint is almost normal and luxation is found on examination. Usually there is no gait abnormality.
Grade 2 - the patella lies loosely in its normal position but will luxate when the joint is flexed. Dogs with a Grade 2 may have a "bunny hop" gait where the patella moves out of the trochlear groove and the dog hops along on the good leg trying to kick the bad leg straight to move the patella back in place.
Grade 3 - the patella is dislocated much of the time but can be manipulated back into the joint when the leg is extended.
Grade 4 - the patella is dislocated all of the time and needs surgery to correct.
In both Grade 3 and 4 the dog shows varying degrees of lameness, often with a bowlegged appearance with the toes pointed in due to the deformity of the rear legs.
Pain is usually not associated with this condition unless it is the result of trauma or until degenerative arthritis has occurred due to chronicity of disease.
The treatment and long-term outcome (prognosis) depend on the severity of disease. Severity is determined how often the kneecap slips out of place, and how easily it slips back into the normal position. Treatment is based upon severity of signs and the affected Cavalier’s age, breed and weight. Conservative therapy (non-surgical) and veterinary observation is often the treatment of choice. However, if the patellar luxation has persistent lameness, or other knee injuries occur secondary to the luxation, then surgery intervention needs to be evaluated.
Cavaliers used for breeding should have within normal limits patellas as determined by an OFA examination at age one. The patellas should be reevaluated as the Cavalier’s ages.