Current research project on patellar luxation in dogs

Patellar luxation (PL) is the lateral displacement (luxation) of the patella from its sliding groove on the femur. It occurs in many breeds of dogs and is often caused by hereditary abnormalities of the knee joint. In small dog breeds, the patella dislocates preferentially to the inside (Medial PL) of the knee. Dislocation to the outside (lateral PL) is less common and occurs mainly in large dog breeds. PL can be unilateral or bilateral. In bilateral PL, normal walking is no longer possible.
In many dog breeds, PL is thought to be hereditary. In order to better combat this orthopedic problem in breeding, a genetic test would be beneficial. We therefore collect EDTA blood samples from PL affected dogs to search for involved genes. As a reference, we also need samples from dogs that have been certified PL-free at the breeding test. Each submission brings us one step further.

Which breeds are we particularly interested in (affected according to OFA)?
Medial PL: Boston Terrier, Chihuahua, Chow Chow, Cocker Spaniel, Coton de Tulear, Dachshund, Eurasier, Fox Terrier, French Bulldog, Japan Chin, Labrador Retriever, Lhasa Apso, Puppy, Norfolk Terrier, Petit Basset Griffon Vendeen, Shar Pei, Sheltie, Shiba Inu, Scottish Terrier, Spitz, Tibetan Spaniel, Tibetan Terrier, Yorkshire Terrier
Lateral PL: St. Bernard, Great Dane, Irish Wolfhound, Pyrenean Mountain Dog

Origin
In the dogs from which samples are sent, PL should not have been caused by an accident or other injury to the knee (traumatic PL).
Hereditary PL may be apparent from birth (congenital) or may not become apparent until the first 4-6 months of life. Causes of luxation of the patella are deviations from the normal bone and connective tissue structure. These include a sliding groove of the femur that is too shallow, a ligamentous apparatus of the knee joint that is too weak, incorrectly attached ligaments and tendons, and malpositions in the knee joint.
The kneecap may slip only briefly and then slide back again (habitual PL) or be permanently displaced (stationary PL).

Diagnosis
The first indication of habitual PL is when the dog occasionally gets out of step when walking and fails to set one hind leg for a step or two. The veterinarian can test for looseness of the patella by palpation and manual pressure and make a definitive diagnosis.
Unilateral stationary PL is manifested by misalignment of the affected knee joint and results in mild to severe lameness. In bilateral stationary PL, dogs bounce or move forward in a waddling gait or with the aid of the front feet only.

Canine patellar luxation
During patellar luxation (PL) the kneecap leaves its normal position in a groove over the thigh bone. This condition is seen in many dog breeds and often has a hereditary background.
The Institute for Animal Genetics and Breeding started a project to investigate the genetic background of PL. For our moleculargenetic analysis we need EDTA-blood-samples of dogs affected by PL or attested as free of PL during a screening examination.

We are especially interested in the breeds (affected by PL according to the OFA):
Medial PL:    Boston terrier, Chihuahua, Chinese Shar-Pei, Chow Chow, Cocker spaniel, Coton de Tulear, Dachshund, Eurasier, French bulldog, Fox terrier, Japanese Chin, Labrador Retriever, Lhasa Apso, Lowchen, Norfolk terrier, Petit Basset Griffon Vendeen, Pomeranian, Pug, Scottish terrier, Shetland Sheepdog, Shiba Inu, Tibetan spaniel, Tibetan terrier, Yorkshire terrier
Lateral PL: Great Danes, St. Bernards, Irish Wolfhound, Great Pyrenees