Patella (Knee-cap) Luxation

Medial Patella Luxation

Springfield District Vets have skilled orthopaedic surgeons who confidently operate on dogs diagnosed with Patellar Luxation. We hope that you find this document useful in understanding the mechanism and surgical repair of this condition. Please do not hesitate to ask for assistance or for a follow-up appointment if you have further questions. We are most happy to assist in any way we can.

The patella (kneecap) runs in a groove between two ridges. Medial patellar luxation (displacement) refers to the patella displacing inwards from its normal position in the trochlear groove. It is common in small breed dogs and may occur simultaneously with other hind limb deformities. In some dogs the inner (medial) ridge does not form well. The animal may be born with the problem or may acquire it over time. Occasionally it may be triggered by a fall.

When patella luxations are present early in life, the major muscle groups of the thigh pull toward the inside of the leg resulting in a bowlegged stance and an abnormal pull on the patella.

When the patella is in its normal position, its cartilage surface glides smoothly and painlessly along the cartilage surface of the trochlear groove. When the patella luxates, or pops over the ridge and out of its groove, these cartilage surfaces rub each other. After some time, the inner ridge wears down and the patella is free to move out or luxate frequently. This can be quite painful and the dog may have difficulty putting weight on the leg. Some dogs learn to kick the leg and push the patella back in place. However, because the ridge is gone, the patella can easily move out of place again. Some dogs can tolerate this problem for a while, but the joint will eventually become arthritic and painful.

Because there is great individual variation in the pathologic deformities seen, a graded classification has been formulated as a basis for recommending which type of surgical repair is most appropriate.

GRADE I
The anatomic alignment of the stifle is normal with the patella luxating only when pushed out of the socket.

GRADE II
The patella luxates upon flexion of the joint and remains luxated until returned by manual pressure.

GRADE III
The patella is permanently dislocated but can be reduced manually with the limb extended.

GRADE IV
The patella is permanently dislocated and cannot be manually reduced.

Treatment

Grade I and some grade II patellar luxations can be treated conservatively. Most grade II and

all grades III and IV luxations should be surgically treated.

The most common surgical procedures:

• The point where the patella ligament is attached is moved and pinned to its more proper location to the more lateral or outer side of the tibia. This corrects the alignment of the leg.
• The groove where the patella sits is deepened so the patella will stay in place. A cartilage sparing technique is generally employed.
• Soft tissue reconstruction procedures – release, relocation and tightening procedures

It is preferred to have this surgery performed before arthritis occurs in the joint. If there is no arthritis, the dog should regain full use of its leg. If there is arthritis already present, it will remain after surgery, especially in cold weather However as the joint will run more smoothly, pain will be significantly reduced.

Possible Complications

1. Complications from surgery include adverse reactions to anaesthesia and infection. Careful aseptic technique and intravenous antibiotics during surgery minimise the chance of infection.

2. Occasionally fluid may build up at the site of the incision (seroma), requiring drainage (aspiration).

3. Sometimes animals have a reaction to the suture material, or to pins. Pins may need removal once the bone has healed, usually within 6-8 weeks. This involves a second, but quite brief general anaesthetic, and generally only a small incision and one or two stitches in the skin.

4. After surgery, the animal should rest until the joint is fully healed to avoid re-injury. The joint may rarely be unstable or the surgical repair may fail and another surgery may be required, especially if the animal is over-active after surgery.

5. Recurrent mild patellar luxation after surgical stabilisation can occur, but are generally of a lesser grade than before surgery, and usually do not require further surgery.

Post-Operative Care

The affected leg(s) may be bandaged for 3 to 5 days. Passive physical therapy is begun immediately after bandage removal to work out the stiffness and re-establish a normal range of motion in the joint. During the next three to four weeks, light walking around the house or supervised short walks outside must be strictly controlled until the muscles strengthen. Swimming can be started after four weeks after surgery. Physiotherapy is strongly recommended to help strengthen the leg, and plays an important part in recovery. SDVC has recommendations for these facilities.

Prognosis

Most patients treated surgically function extremely well and do not show further lameness. The improved limb alignment and joint stability will reduce but not halt the progression of pre-existing arthritis. Many factors but most particularly the degree of pre-existing arthritis, the presence of associated ligament or joint cartilage damage and the grade of the luxation influence the prognosis. Ongoing medical management for arthritis includes exercise, diet and weight management, formulated medications and supplements. SDVC staff are most happy to assist in all of these areas.

*NOTE: Patella luxations are usually heritable, so these animals should not be used for breeding.