Luxating Patella

Patellar luxation is the dislocation (slipping) of the patella (kneecap).  In dogs the patella is a small bone that shields the front of the stifle joint.  This bone is held in place by ligaments.  As the knee joint is moved, the patella slides in a grove in the femur.  The kneecap may dislocate toward the inside (medial) or outside (lateral) of the leg.  This condition may be the result of injury or congenital deformities (present at birth).  

Patellar luxation can affect either or both legs.  The most common occurrence of luxating patella is the medial presentation in small or miniature dog breeds, though there has been a marked increase in certain Bull Breeds more notably the heavier Bull Breeds and  breeds with well sprung hind quarters particularly the Staffordshire Bull Terrier.  Shallow femoral groove, weak ligaments and malalignment of the tendons and muscles that straighten the joint are all conditions that will predispose a dog toward luxating patellas.           

Indications of patellar luxation are; difficulty in straightening the knee, pain in the stifle, limping, or the tip of the hock points outward while the toes point inward. 

The diagnosis of this condition can usually be confirmed (by a veterinarian) by manipulating the stifle joint and pushing the patella in and out of position. 

Patellar luxations fall into several categories: 
 
Categories 1, 2, and 3 are either hereditary or strongly suspected of being inheritable. 
Beyond the categorization of patellar luxation there are 4 grades of deviation for this condition: In any case breeding from any dog with this condition should be strongly discouraged.

Grade 1 are patella luxations that are found on physical exam by  
looking for them when the dog shows little to no clinical signs -- the patella 
can be luxated manually but doesn't do this much on its own. 

Grade 2 luxations occur when there is occasional spontaneous lameness  
but the patella returns to normal positioning easily enough that the dog 
usually isn't pained much by it. This is typically the dog that 
occasionally carries a rear leg for two or three steps on occasion but 
then puts it back down and goes as if nothing was wrong. 

Grade 3 luxations is usually used to describe dogs who are beginning to  
have a loss of function due to the luxation of the patella. They have 
more frequent "skipping" episodes, may not want to jump up onto things, they 
may have pain and the patella doesn't always return to normal positioning 
when it is deliberately pushed out of its groove during a physical 
examination. 

Grade 4 luxations are when the legs are painful enough that the dog  
tries not to use them, when the leg can not be fully straightened manually 
and the dog shows evidence of chronic pain or disability, including poor to 
no ability to jump. 

Grade 5 (or severe grade 4 depending on the grading scheme) is when the  
dog won't use the legs or when the gait is stiff legged due to the patella 
being underdeveloped or permanently dislocated and fixed in place 
outside its normal position. 

Concurrent cruciate ligament injury may be present in dogs that have a dislocating kneecap, therefore this may also need to be addressed

Prognosis generally is very good - the higher the grade of the patellar luxation, the greater the failure rate unless more corrective surgeries are done   Clinical signs

Lameness  

a skipping gait  

pain  

stiffness of the hind limb  

Some pets show only a single sign, whereas others show many signs of the condition  

Failure to treat the condition could lead progressive debilitating arthritis of the joint  

  
Surgery

If the groove that the patella rides in is shallow or misshapen, it is surgically deepened; we usually use an advanced technique to perform this called the block osteotomy  

If the attachment of the patellar ligament to the tibia, called the tibial crest, is in the wrong position, it is repositioned  

The capsule of the knee joint is tightened; this tightens the femoropatellar ligament  

In some dogs the femur bone is fairly twisted and needs to be cut and realigned  

A support bandage is usually not used after surgery so that physiotherapy can be started soon after surgery  

 

Convalescence

By 10 to 14 days after the surgery your pet should be touching the toes to the ground at a walk  

By 2 to 3 months after surgery your pet should be using the limb well  

If your pet does not follow a normal progression of recovery, the surgeon should be notified  

 
Prognosis

Surgery has approximately a 90% success rate. Success is defined as the return of good function of the limb  

Unfortunately surgery will not remove the arthritis that may already be present in the knee. As a result, your pet may have some stiffness of the limb in the mornings or after laying down for a nap. In addition, your pet may have some lameness after heavy exercise  

By having the surgery done earlier, the chance of developing significant arthritis is decreased  

Dogs that have a higher grade of patellar luxation may have increased risk for reluxation of the patella  

Large breed dogs that have patellar luxation may have increased risk for reluxation of the patella if a corrective femoral osteotomy is not performed  

 
Potential complications

There is an inherent risk of anesthetic death with any procedure requiring anesthesia, however, this is very small  

Infection of the surgical site, although not common, can occur  

Cage rest is vital, if exercise is not minimized for 8 weeks after the surgery, breakdown of the repair may occur, thus requiring  a second surgery.