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Canine Hind Leg Diagram

Patellar luxation, or knee dislocation, can range in severity from a knee that dislocates when extended completely and snaps back into place to a knee that is permanently dislocated medially (toward the center of the dog’s body).

Cause

One of the causes of patellar luxation is an abnormal shape of the distal end (the end furthest away) of the femur, resulting in a shallow patellar groove. The kneecap sits in this groove, allowing the kneecap to move back and forth.

The other major cause is a displacement of the quadriceps tendon's attachment to the tibia so that the patella is displaced medially (towards the middle) when the quadriceps muscle is flexed.

The tendency to luxate to the medial side causes a transient lameness, at least until the patella returns to its normal position, if possible. The extent of patellar luxation increases with time as the femur's trochlear groove becomes flatter, as increased bowing of the leg takes place, and as the structures of the stifle joint weaken.

Continued deformity of the joint results in degenerative joint disease, pain, and decreased mobility.

Patellar luxation can be caused by defects in your dog’s anatomy or by injury. It is a common condition and can be genetic, but not all cases are. It is uncommon in cats.

Some breeds have a higher incidence than others. Breeds known to have this condition include:

Severity

Dislocation is graded by severity. Four grades of dislocation are recognized:

Grade 1: The patella luxates with manual pressure and returns spontaneously. Dogs may not show any signs and may not require treatment.

Grade 2: The patella luxates with joint flexion and extension but returns to the patellar groove spontaneously. Some lameness and minimal degenerative joint disease may be present. Conservative management and supportive care may be all that is needed.

Conservative therapy includes rest, physical rehabilitation, chondroprotective agents (disease-modifying drugs used for osteoarthritis, known as DMOADs), and nonsteroidal anti-inflammatory drugs (NSAIDs).

Grade 3: The patella luxates with joint flexion and extension but can be reduced manually. Considerable lameness exists.

Grade 4: The patella is permanently luxated to the medial side. The limb or limbs are unable to extend and the dog walks while balancing their weight on the forelimbs.

Treatment

Treatment is dependent on the clinical signs, the severity of luxation, and the age of the dog.

If your dog has frequent or bothersome clinical signs (frequent or persistent episodes of lameness) of patellar luxation of any grade, your veterinarian may recommend surgery.

Dogs with Grade 3 or Grade 4 luxation most often benefit from surgery, while dogs with Grade 2 luxation may benefit if they show those signs. After surgery, the dog's activity is usually restricted for six to eight weeks.

Post-Surgical Support

Supportive therapy is implemented for mildly affected dogs and for those recovering from corrective surgical procedures. Supportive care includes analgesics, exercise restriction, physical rehabilitation, and weight reduction for overweight dogs. Various analgesics are available to relieve pain in dogs, with and without degenerative joint disease. Chondroprotective agents may also be considered.

Physical Rehabilitation 

Physical rehabilitation measures can include low-impact activities, massage, hydrotherapy, and range of motion, strength, and flexibility exercises. These techniques can help accelerate postoperative recovery.