Typically a developmental disorder of the hind limb(s), where improper bone and ligament conformation allows the patella (kneecap) to become displaced out of it’s normal position. This can affect normal limb function, resulting in discomfort, lameness and in some cases, crippling deformity, loss of joint mobility and painful osteoarthritis. This problem can also be the result of traumatic injury or made worse through repetitive athletic strain to the joint.
Symptoms: Abnormal gait due to dislocation of the patella, skipping, hopping in one or both hind limbs or keeping the affected limb raised and not using it. Palpation of the limb may reveal that the patella can be moved out of it’s normal position to the inside or outside of the femoral groove in the knee joint. Some dogs may be seen to extend or shake their hind leg in order to ‘pop’ a temporarily dislocated patella back into it’s proper position. Dogs affected by more severe cases where the patella is permanantly out of place, often will move with their hind legs in a crouching, bowlegged position, with hind feet turning inward and weight being carried more in the front. If the problem is injury related, the joint may be swollen and painful and may also involve a strain or tear to the cruciate or other ligaments of the joint.
Patellar Luxation can vary widely in severity and has been graded for evaluation on a scale from 1-4:
- Grade 1 Patella can be manipulated out of its groove, but returns to its normal position spontaneously.
- Grade 2 Patella moves out of its groove occasionally and can be replaced in the groove by manipulation.
- Grade 3 Patella remains out of its groove most of the time but can be replaced in the groove via manipulation.
- Grade 4 Patella stays out of its groove all the time and cannot be replaced inside the groove.
Grades 1 and 2 may remain asymptomatic and can be treated conservatively with little or no intervention unless there is progression to more severe conditions. Athletic activities may produce this result, increasing risk for painful damage to cartilage (chondromalacia) and ligaments of the joint.
Grade 3 and 4 often requires surgical correction and physical therapy and if left untreated there is greater risk for permanent loss of joint function and lameness.
Mode of Inheritance: unknown in Cardigans, but in other breeds it is thought to be an autosomal recessive with polygenic and environmental factors. There is evidence that it is linked to limb development, particularly in the depth of the femoral trochlear groove and balance in bone, muscle and ligament development, particularly the rectus femoris muscle. In larger, heavier boned breeds the shape and angle of the femoral head in approximation to the hip joint may play a role.
Age of onset: Variable, but can typically be identified by palpation before age 1. Grade 3 and 4 luxation may be identified as early as 3-4 weeks and puppies with any grade of luxation can begin to exhibit symptoms by 5-6 months of age.
- Cardigan: yes
- Pembroke: yes
- Other Breeds: yes, many breeds and mixed breeds.
Incidence in Cardigans: According to OFA, 7.1 percent of the 42 cardigans evaluated before December, 2011 were identified as having an abnormal rating. Out of the three cardigans identified with patellar luxation in the open database, two are Grade 1 and one is Grade 2. Other cases of more severe luxation have been reported informally, but not submitted to OFA.
- Cardigans: no
- Other breeds: yes, primarily Pomeranians and Flat Coated Retrievers, but including Bichon Frise, Shar Pei and Chihuahuas.
- Active?: no
Registry: yes, the OFA offers a Patellar registry and health clinics including Patella evaluations for OFA submission have been offered at shows by some kennel clubs.
Links to register: OFA’s Patellar Registry Application.
Tests Available: Some genetic markers have been explored, but there are no DNA tests currently available. Phenotypical testing can be done to identify affected individuals. Testing involves a physical palpation of the patellae by a qualified veterinarian, which can be done as part of a regular visit. No anesthesia is necessary and the cost to submit to the OFA registry is very affordable, with no charge for submission of affected individuals.
Published papers and Articles:
- Incidence and genetic aspects of patellar luxation in Pomeranian dogs in Thailand.
- Patellar luxation: Pathogenesis and surgical correction
- Human research: Knee osteoarthritis, lumbar-disc degeneration and developmental dysplasia of the hip – an emerging genetic overlap
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