Medial Luxating Patella in Dogs


What is a Medial Luxating Patella?

A medial luxating patella, is an extremely common problem in toy breed dogs. An owner typically notices a little skip in the dog’s step. The dog may even run on three legs, holding one hind leg up, and then miraculously be back on four legs as if nothing has happened.

However in some cases, something has happened: the kneecap (patella) has slipped out of the smooth groove in which it normally rides up and down. It has slipped medially towards the other leg. With the patella dislocated (or luxated) medially, the knee cannot extend properly and stays bent.

With luck, some patients will be able to slip the kneecap back where it belongs and be back to normal in only a few steps. For some dogs, getting a kneecap back where it belongs and normal extension of the rear leg is a mere dream only attainable with surgical correction. Approximately 50 percent of affected dogs have both knees involved while the other 50 percent has only one knee involved.

Grading the Severity

In dogs, medial patella luxation's are graded to assess severity and therefore correction options.

Grade 1:

The kneecap can be moved out of place manually but will fall back into its natural position once the manipulator lets go.

Grade 2:

The kneecap occasionally slips out of its groove, spontaneously creating an intermittent lameness. The kneecap will go back in place on its own. Whether or not it needs surgery depends on several factors: how often lameness is a problem and how long the lameness lasts when it is a problem. Another reason to proceed with surgical intervention is for prevention. If the ridge of bone on the inside of the knee wears down, the Grade 2 will progress to Grade 3. This progression can be prevented with surgery.

Grade 3:

The patella is out of place all the time but can be manipulated back into its normal position manually (though it will not stay there). At this point, the dog may seem to crouch or slant down in the rear. Lameness or rear weakness may be persistent. The dog may have a bow-legged appearance.

Grade 4:

The patella is out of place all the time and no amount of manipulation can return it to its proper place. Such a dog has extreme difficulty extending his knees and walks with his knees bent virtually all the time in a somewhat crouched position. In this situation, the rotation in the long bones that accompanies the luxation will interfere with surgical correction and total resolution of the lameness may not be possible.

Does my Dog Require Surgery?

Dogs with Grade 1 - Do not require surgical repair. Often they can be managed with weight control and periodic anti-inflammatory medications.

Dogs with Grade 2 – Surgery is very beneficial in the long term health and comfort of your dog but is elective.

Dogs with Grade 3 or 4 - Surgery is required.


Risks Should Surgery Not be Performed

It is not a good thing to have one’s knee cap out of place; the entire weight-bearing stress of the rear leg is altered which, in time, leads to changes in the hips, long bones, and ultimately arthritis. How severe the changes are depends on how severe the luxation is (i.e., the grade as described above) and how long that degree of luxation has been going on. In time, the legs will actually turn outward with its muscles turning inward, making the dog bow-legged. The luxation is not considered a painful condition but after enough time and conformational change, arthritis sets in, which is indeed painful.


Surgery for Medial Luxating Patella's

Surgery for a medial luxating patella is a procedure that not all veterinarians are comfortable performing. Maraboon Veterinary Surgery has done extensive training in this field and are extremely competent in correcting these types of abnormalities.

One major reason why we recommend dog's luxating patella's to be repaired is that there is an extremely high correlation in dogs with luxating patella's going on to tear their cruciate ligaments.  Although correcting the luxating patella does not guarantee that your dog will not rupture its ligament, it improves the anatomy of the joint and therefore decreases the risk.  If your Veterinarian has diagnosed your dog with concurrent luxating patella's and a torn cruciate ligament, please click here for more details on the repair required.


What Happens During the Surgery

There are 3 small corrections done during surgery to correct these luxating patella's, they are all done in one surgery and provide the most favourable outcome.

Lateral Imbrication

When the patella slips out of its groove, the joint capsule surrounding it is stretched to allow this motion. Imbrication simply involves making a tuck in the joint capsule. The tightened joint capsule does not allow for the slipping of the kneecap and the kneecap is confined to its proper groove.

Trochlear Modification

The patella rides in a groove at the bottom of the femur (thigh bone). In toy breed dogs this groove is shallow, which allows the patella to slip. If the groove is deepened, the patella stays where it belongs. The normal groove in the femur is lined by slippery lubricated cartilage, called hyaline cartilage. This cartilage is peeled or cut away, so the bone underneath is sliced out to form a deeper groove, and the cartilage is replaced.

Tibial Crest Transposition

If the knock-kneed conformation has already started to set in, the tibias (or leg bones) will have rotated. In particular, the crest on the tibia where the thigh muscle (the quadriceps femoris) attaches may have migrated inward. If this is the case, the crest will have to be removed and pinned back where it belongs to straighten out the leg.


Cost of Surgery

The cost of these procedures varies based on the size of the dog, age, and if has concurrent cruciate rupture.

Costs for correction of a simple luxating patella are as follows:

  • Under 10kg dog - Surgery is approximately $2350
  • 10kg-20kg dog - Surgery is approximately $2550
  • 20kg-30kg dog - Surgery is approximately $2750
  • Over 30kg dog - Surgery is approximately $2950 

The cost of the surgery includes:

  • Includes a series of 4 cartrophen injections, which provides pain relief by acting on the pathology within the joint that causes pain and lameness. These are given weekly for 4 weeks (first injection is done on the day of surgery then again on days 7, 14, 21 during the post op checks).
  • Includes post op rechecks at time, (when cartrophen injections are given) and includes a discussion about physiotherapy and return to exercise options.
  • Includes post op take home medications.
  • Includes post op radiographs (done on day of surgery).
  • Includes post op radiographs required at 8 weeks post surgery.
  • NOTE the above price EXCLUDES any additional post op checks and medications (which are not typically required) if post op instructions are not followed!
  • Surgery can be preformed at Maraboon Veterinary Surgery.

Note if your dog is unfortunate enough to have a luxating patella and a torn cruciate ligament please click here to get information on the repair of the cruciate ligament and options for repair.  Costs vary depending on what technique you choose for repair.

Should both Knees be Repaired at the Same Time or should they be Staged?

Most surgeons feel that doing one leg at a time, 8 weeks or more apart, is beneficial as the patient will have one good rear leg which they can use to walk on. 

Post-operative Care

Expect six to eight weeks of confinement. During this time easy walking (no running or jumping) is helpful. The dog should be using the leg by two weeks post-operation, though some dogs must be retrained to use the leg after surgery. Physical therapy will be required if the dog is not using the leg after one month.