Loose Patella

Loose patella (also known as luxated patella, patella laxity or slipped stifles) is a common condition which generally affects small dog breeds.  It is more common in females than males, though the reason is unknown.  The Patella is another name for the rear knee joint and it is very similar to a human knee.  In a normal knee, the upper and lower leg bones are lined up so that the patella (kneecap) and the tendon ride in a smooth groove.  The function of the patella is to protect the large tendon that runs from the upper leg bone to the lower leg bone.  When the knee is extended and bent, the patella should ride smoothly to protect the tendon.  

Patella luxation occurs when the joint is not in proper alignment.  This allows the tendon and patella to slip out of the groove and ride instead on the inner or outer surface of the joint.  When this occurs, the upper leg muscle is unable to extend the leg, resulting in lameness and abnormal gait.  Over time, the patella will become damaged due to contact with the rough surface of the bone instead of the smooth surface of the groove .  This can lead to arthritis and permanent damage to the joint.  This action also leads to a twisting of the leg caused by the upper leg muscle.  The additional strain on the joint may also lead to other damage to the joint.

Signs of luxation may be present at birth or may not present themselves until later in life.  A dog may begin with intermittent lameness, carrying of one or both rear legs, or a “skipping” motion while walking or running.  There are four Grades of patella luxation ranging from the ability to manually move the patella, which is the least severe and often graded as Grade I.  Grade IV is the most severe and the dog's leg appears bowed and is carried off the ground much of the time. 

Patella luxation can be fixed by varying means including surgery.  However, the higher grades may be more difficult to fix and in some cases,  the joint may never be normal.  Some affected dogs are born without the groove (trochlea) in which the tendon and patella ride.  In this case, the surgery to repair the condition is very costly and may require the removal of bone in order to build a groove.  The recovery time for this type of treatment is long and may never result in a proper joint.  It can also be a very costly procedure that may require internal pinning as well as temporary external pinning of the joint.  

Screening of breeding dogs is one way to prevent this congenital disease.  Choosing to avoid the breeding of affected animals is the best way to reduce the number of animals affected by patella luxation.  Sound breeding of dogs that do not carry the gene for patella luxation allows for the least chance of carrying this condition down through generations of dogs.