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Luxating Patella

Liaison: Deb Thompson
Email: Deb.Thompson@sas.com

Luxating patella or dislocation of the knee, is a condition where the patella or kneecap moves out of its normal location. The patella, or knee cap, should be located in the center of the knee joint.  There are two types of luxation:

  • Medial: Also known as MLP, is the most common. This is where the patella slips to the inside. MLP is congenital in origin, and appears most often in smaller breeds. Typically shows up in the first year of life and is usually bilateral (both knees are affected).
  • Lateral: Patella slips to the outside. Typically caused by some type of trauma or injury but can be congenital.

Dislocation of the kneecap is painful and may result in lameness. When the patella luxates (jumps) out of the trochlear groove of the femur, it usually cannot return to its normal position until the quadriceps muscle relaxes and increases in length. This is why the affected dog may be forced to hold his leg up for a few minutes or so after the initial incident. While the muscles are contracted and the patella is luxated from its correct position, the joint is held in the flexed or bent position. The yelp is from the pain caused by the knee cap sliding across the bony ridges of the femur. Once the patella returns back into the groove the pain is gone and the dog will usually resume normal activities. Lameness is often intermittent and may be non-existent in some dogs.

 

 


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Signs and Symptoms

  • Lameness
  • A skipping or a stiff gait, almost as though the leg can not be bent.
  • The leg may be turned inwards, and a lump may be obvious by feeling along the inner or outer leg.
  • Pain
  • Sudden crying out in pain when running. The affected leg will be extended rearward, and for a while, the dog is unable to flex it back into the normal position.
  • Stiffness of the hind limb
  • Arthritis can develop as a secondary symptom.
  • Some pets show only a single sign, whereas others show many signs of the condition

Dogs with Luxating Patellar can be divided into 3 classes:

  1. Neonates and older puppies often show clinical signs of abnormal hind-leg carriage and function from the time they start walking; these present grades 3 and 4 generally (see below for explanation of grading system). Uncommon in Samoyeds.
  2. Young to mature animals with grade 2 to 3 luxations usually have exhibited abnormal or intermittently abnormal gaits all their lives but are presented when the problem symptomatically worsens. Less common in Samoyeds.
  3. Young to mature animals with grade 1 and 2 luxations may exhibit sudden signs of lameness because of further breakdown of soft tissues as result of minor trauma or because of worsening of degenerative joint disease pain. Most common type in Samoyeds.

 

Signs vary dramatically with the degree of luxation. In grades 1 and 2, lameness is evident only when the patella is in the luxated position. The leg is carried with the stifle joint flexed but may be touched to the ground every third or fourth step at fast gaits. Grade 3 and 4 dog’s exhibit a crouching, bowlegged stance with the feet turned inward and with most of the weight transferred to the front legs.

Veterinarians may use either a 1-5 (some sources use 1 to 4) grading system:

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. Dog may have no symptoms.

Grade 2 luxations occur when there is occasional spontaneous lameness but the patella returns to normal positioning easily enough that the dog usually shows little pain.  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 on as if nothing was wrong.

Grade 3 luxations are usually used to describe dogs that 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 cannot 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. 


Causes

Luxation may result from traumatic injury or congenital (present at birth) deformities. A birth defect where the legs turn inward may also be a cause. If the trochlear groove that the patellar ligament (knee cap) rides in is too shallow or if the distal attachment of the patellar ligament is medial instead of central, the patella will dislocate medially when the knee is bent.  When this occurs, the dog has difficulty bearing weight on the leg until the ligament snaps back into place.  Sometimes only one knee is involved, but the disease can become bilateral (involving both legs) in about 50% of cases.

 


Risk Factors

Patellar luxation is most common in toy and miniature dog breeds.


Diagnostic Tests

Patellar luxation is diagnosed based upon history, physical exam findings (palpitation of the knee), and may use x-rays to confirm the diagnosis.

 

 


Treatment Guidelines

Note: Treatment of animals should only be performed by a licensed veterinarian. Veterinarians should consult the current literature and current pharmacological formularies before initiating any treatment protocol.

Medical therapy has little corrective ability in this disorder and surgery is therefore the treatment of choice. Surgical treatment is not necessary in every individual with this condition. Surgery is performed to improve function of the leg; therefore, if the animal is not lame, surgery is not indicated.

The decision to perform surgery on dogs with patellar luxations is based on many factors including the degree of lameness, the grade of patellar luxation, the age of the animal, and the presence of concurrent problems with the knee.

A low grade MLP, which has been present all of the animal's life, without a history of lameness, would not indicate surgery is needed. Arthritis may develop, whether or not surgery is performed.

Patellar luxation may also be found in conjunction with other injuries to the knee which require surgery, most commonly, rupture of the cranial cruciate ligament. Often the surgeon will discuss correction of the patellar luxation at the same time the other injury is repaired.

Most veterinary orthopedic surgeons recommend repairing dogs in Grade 3+ without question and advocate fixing grade 2 dogs frequently. Most dogs generally get worse over time and move from Grade 1 to Grade 2 or from Grade 2 to 3, for example. The changes may not happen until later in life, though. A lot of dogs with Grade 1 or Grade 2 patella luxation early in life will have pretty stiff knee joints by the time they are old. This probably is at least partially due to arthritis from the years of luxating patellae.

 

If the surgery is performed before arthritis occurs, the prognosis is excellent.  Your dog should regain full use of its leg.  However, if arthritis has already occurred, your dog will experience pain in the joint, especially in cold weather.

 

Surgery will alter both the affected structures and the movement of the patella. The groove at the base of the femur may be surgically deepened to better contain the knee cap (called a block osteotomy). The capsule of the knee joint is tightened; this tightens the femoropatellar ligament. The knee cap itself may be 'tied down' laterally (on the outside) to prevent it from deviating medially (toward the inside). The bony protuberance at the site of the attachment of the quadriceps tendon on the tibia may be cut off and then re-attached in a more lateral position.

 

All of these procedures work well and the type performed depends on the individual case and the Surgeon.  Recovery time post-surgery is varied and depends upon weight and age of the pet, pet’s physical activity, and degree of involvement of the surgical procedure. 

 

Most pets will begin touching their toes to the floor in 2 to 4 weeks.  By 2 to 3 months after surgery your dog should be using the limb well.

 

If your dog requires surgical correction of both knees, they will generally be operated approximately 6 weeks apart. This is to allow the one leg to recover from surgery and strengthen prior to performing surgery on the second side. In smaller dogs they may operate on both knees at the same time, but this would not be advisable in a Samoyed or other larger dog.

 


Management

With Surgery

  • 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 dog 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.
  • Dogs that have a higher grade of patellar luxation may have increased risk for reluxation of the patella. Larger dogs also may have increased risk for reluxation of the patella if a corrective femoral osteotomy is not performed
  • If a dog licks his incision it will actually delay the healing process because they usually lick too much and traumatize the area. Licking can remove stitches and cause the incision to open, it can also cause infection. Licking can become a severe habit that is difficult to break.  Dogs will frequently lick the incision when the owner is not watching such as at night time; if the skin looks red or excoriated the most common cause is from licking.
  • To stop your dog from licking the following can be tried:
    1. Elizabethan collar can be placed on the neck; this will not help stop your pet from scratching at the region
    2. Cervical collar (bite not collar) is a less awkward device and can be effective at stopping a pet from licking the surgical site
    3. Bitter apple can be applied around the incision; many dogs will continue to lick  after application of this topical
    4. Bitter Apple and Liquid HeetTM (obtain this from a drugstore...it is used for sore muscles) mixed in a 2:1 ratio can be applied around the skin incision
  • The standard post-operative recommendations are to use a padded bandage for 3 to 7 days after the surgery to control swelling and provide some support. After the bandage is removed, it is recommended most frequently that leash walking only be allowed for 4 to 6 weeks. Some texts recommend passive physical therapy (moving the joint through its range of motion manually for 40 to 50 times once or twice a day) as well. Swimming is occasionally recommended, after the incision has healed.
  • There are some patients who simply don't respond to surgeries as expected. Sometimes even when the
    surgery goes well, the post-operative care was good but the surgical outcome was still not optimum. This is probably more common in orthopedic surgeries than in other forms of surgery, since there can be
    hidden changes in bone or joints and sometimes fixing one problem creates pressures or problems in other areas.

Without Surgery

  •  Activity may be normal to restricted based upon severity of disease.
  • Weight control is important in treating this disease condition.  Excess weight increases the load and stress on the knee joints.
  • Anti-inflammatory medications may be given for inflammation and pain control. 
  • Nutritional supplements are available to help decrease arthritis and maintain as normal and healthy of a joint as possible. 
  • Additional help can be given with the use of pet ramps, stairs, or steps. These can help the dog travel from one place to another, especially up and down, without adding any pain or damage to the patella.   

Support Groups

 

Orthodogs Yahoo support group http://tech.groups.yahoo.com/group/orthodogs/


Suggested Links

OFA Registration

The Orthopedic Foundation of America will issue registration numbers to dogs whose patellar have been examined and manipulated by a vet, forwarded to the OFA, and found to be normal. For More Information visit the Orthopedic Foundation of America

 

ACVS - Medial Patellar Luxations  three bones rating

http://www.peteducation.com/article.cfm?cls=2&cat=1569&articleid=457 two bones rating

http://www.vetsurgerycentral.com/patella.htm  two bones rating

http://www.ovrs.com/docs/brochures/PatellarLuxation_surgery.pdf    two bones rating 

http://www.offa.org/pl_overview.html   three bones rating

http://www.cpvh.com/2011/07/27/luxating-patella-knee-cap/  two bones rating

Merck Veterinary Manual Online - Patellar Luxations four bones rating


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