Patellar Luxation

Patellar luxation is a condition in which the patella, or ‘kneecap’, is displaced from its normal location in the trochlear groove on the front of the knee. Patellar luxation may be induced by trauma but is more commonly a congenital (present at birth) condition in the toy and miniature breeds such as the Yorkshire Terrier, Chihuahua, Miniature and Toy Poodles, Pomeranian and Pekingese. Luxation (dislocation) can occur either direction, medial (to the inside edge of the knee) or lateral (to the outside edge of the knee). In smaller breeds, medial luxation is more common. Lateral luxation can occur in any dog but is more common in the large and giant breed dogs, especially Newfoundlands and Great Pyrenees. Patellar luxation may occur simultaneously with other pelvic limb deformities. While the definitive sequence of events which produces these deformities has not yet been established, the age at which the syndrome occurs does play an important role in the severity of the deformities and the degenerative changes that develop in the joint.

When the patella is in its normal position, its cartilage surface glides smoothly and painlessly along the cartilage surface of the trochlear groove. As the patella slips out of its groove these cartilage surfaces rub each other in an abnormal fashion. Your pet may cry and try to straighten (extend) its leg to pop the patella back to its normal position or may hold the limb up until muscle relaxation allows the kneecap to reposition itself. In this situation you will only see an intermittent lameness. There is little or no discomfort until the cartilage is eroded to the point where bone contacts bone. From this point on, each time the patella slips out into its abnormal, luxated position it will cause pain. This explains why many individuals have no clinical lameness until they reach adulthood. Although the problem has been present for many months or even years, progressive cartilage wear creates an acutely painful condition.

Because there is great individual variation in the deformities seen, a graded classification of medial patellar luxation (Putnam 1968) has been formulated as a basis for recommending when surgical intervention is needed.

Grade I: The anatomic alignment of the stifle is normal with the patella luxating only when pushed out of the trochlear groove. This is usually an incidental finding at your pet’s annual physical exam and does not require surgical intervention.

Grade II: The patella is usually located in the trochlear groove but will luxate upon flexion of the joint. It will remain luxated until the knee joint is manipulated or it is reduced by manual pressure. These patients may require surgical intervention if symptoms occur frequently or if they are very painful.

Grade III: The patella is permanently luxated but can be reduced manually with the limb extended. Surgery is almost always recommended for these patients. This grade is often accompanied by other rear limb deformities that may require concurrent surgical correction.

Grade IV: The patella is permanently luxated and cannot be manually reduced. This grade is frequently accompanied by other pelvic limb deformities that often require concurrent surgical correction.

Treatment

The procedures for repair of patellar luxation deal with repositioning and stabilizing the kneecap in the trochlear groove of the femur. Depending on the severity of the deformities, the techniques may be as simple as soft tissue reconstruction or as complicated as multiple corrective osteotomies (straightening the bone).

Surgical correction generally involves:

• Trochleoplasty - deepening the trochlear groove.
  
• Capsular and fascial imbrication - tightening the tissues around the joint.
  
• Tibial tuberosity transposition - repositioning the point of patellar ligament attachment to the tibia so that it is aligned with the trochlear groove.

In severe cases where concurrent deformities of the long bones of the limb (femur and tibia) are present, corrective osteotomies (cuts made in the bone to allow realignment of the limb) may be necessary.

Post-operative Care

After surgery is completed rehabilitation therapy is begun immediately to help reduce pain and to help your pet to return to full function as early as possible. This process will be continued at home. You may also enlist the services of the staff of the Animal Rehabilitation Center of Rochester for outpatient treatments and application of more advanced rehabilitation techniques that will help your pet recover faster and more completely.

Exercise restriction will be employed as determined by your doctor. For most patients this will involve crate rest and short leash walks only. Exuberant activity must be avoided during the early stages of recovery to allow your pet to heal without complications.

Prognosis

As a general rule, the prognosis is better when surgery is performed early stages of disease. For dogs with Grades II and III luxations, prognosis is generally good but is affected by the severity of arthritis present within the joint and the severity of bony malformation in the limb. Grade IV luxations carry a guarded prognosis. If they are treated very early in the disease process and rehabilitation therapy is initiated promptly and aggressively after surgery a fair prognosis for return to function can be given.

As patellar luxation is most often a congenital problem it is probably genetic in origin. Therefore, breeding of affected animals is not recommended; however, this problem is so prevalent in some breeds it may be impossible to do so. Patellar luxation can also be traumatic in origin, but this is a much less common presentation.