PATELLA LUXATION

The patella, or kneecap is a small bone that protects the front of the stifle joint.   

Patella luxation is a relatively common condition in the Yorkie and often results in the intermittent lifting of one or both hind legs when walking or running. It is possibly recessively inherited and therefore it is sensible not to breed from afflicted animals. Today, veterinary orthopedics are such that corrective surgery is usually extremely successful.

The patella is anchored in place by ligaments and slides in a groove in the femur called the trochlea.  If the groove is too shallow, the patella will slip out when the knee bends. When the patella slips out to the inside of the knee joint, it's called medial luxation.  When it slips out to the outside, it's called lateral luxation.  

Medial luxation is more common.  It occurs in toy, miniature, and large breeds, and is apparent in some pups when they begin to walk. The patella may slip in and out of place, resulting in a gait that is sometimes normal and sometimes not.  When the patella is out of place, the affected leg is usually carried with the stifle joint bent and the foot turned inward.

Lateral luxation occurs in large and giant breeds at five to six months of age.  A knock-kneed stance is the most noticeable sign.  The foot often twists outward as weight is placed on the limb.  Both knees are almost always involved.

The diagnosis of luxation is made by attempting to push the patella out of the trochlear groove.    The degree of luxation is graded 1 to 4, depending on how easy it is to dislocate the patella and whether the patella returns spontaneously to the trochlear groove.  

Treatment:  involves surgery to deepen the trochlear groove and repair any loose or torn ligaments.  The specific operation depends on the age of the dog and the type of luxation.  Dogs with genetically determined patella luxation should not be bred.

Preliminary veterinary screening for medial patella luxation should be done on Toys and small breeds at six to eight weeks of age, before these pups are sent to their new homes.

The OFA* maintains a patellar luxation registry and issues certificates to all dogs that palpate normal at 12 months of age or older.  The GDC* maintains a medial patella luxation registry for breeds in the Terrier Group and also issues certificates to acculullate information on patella luxation based on palpating patellas when dogs re X-rayed for hip dysplasia.

Dogs with genetically determined patella luxation should not be bred.

OFA - Orthopedic Foundation for Animals

GDC - Insititute for Genetic Disease Control in Animals

Information compiled from Dog Owner's Home Veterinary Handbook and The 5-minute veterinary consult.