The knee of the dog, not unlike that of humans, is a very complex joint and subject to great stresses. It is supported by strong ligaments on both sides, by the kneecap with its associated muscles and by ligaments in front. Inside the knee are two cartilage pads (menisci) and the two cruciate ligaments. This combination of complexity and stress make the knee the most commonly injured joint.

The most frequent knee injury in the dog is rupture of the cranial cruciate ligament. This may be the result of an injury while running or jumping, but can sometimes be the result of a slower degenerative process. Sometimes the menisci or other ligaments can be injured at the same time.

The cruciate ligaments form a crossing pattern inside the joint. Their purpose is to allow the knee to flex but to prevent excessive sliding motion. When one of these ligaments is torn, a slight sliding motion occurs each time that weight is placed on the limb. This stretches the supportive tissues around the joint which causes pain. If this instability persists over a long period of time it also causes chronic inflammation, which in turn leads to degenerative joint disease and arthritis. Also, long-term shifting of weight to the other limb can predispose it to injury. Surgical treatment of cruciate ligament injuries therefore serves two purposes—relief of pain and slowing progression of degenerative joint disease.

HOW IS THE INJURY TREATED?
Some small breeds will regain normal function with time, restricted exercise and medication if no surgery is done to stabilize the joint. Most large breeds will require surgery to avoid degenerative joint disease. Injections of chondroprotective drugs such as Adequan are given to minimize degenerative changes.

WHAT IF MY PET NEEDS SURGERY?
The knee joint is opened and remnants of the old ligament are removed. The cartilage pads are examined for damage and repaired, if necessary. In smaller breeds, a new ligament is then fashioned from a strip of fascia (a tough fibrous tissue covering the thigh muscle) or synthetic material. In larger breeds, a procedure called TPLO is done. The actual technique may vary with the patient.

The success rate of cruciate surgery is good. Almost all patients regain normal use of the limb and live a happy and pain free life. An occasional slight limp may be noted, but rarely does this affect the patient’s life style.

Your pet will probably carry the leg for about 2 weeks before attempting to bear weight. Physical therapy is more difficult with our pets than with humans but it can be done and is certainly helpful. It can take 3 – 4 months for the joint to reach full strength, so restricted exercise is crucial during this time no matter how good the patient may feel.

As with any major surgery, there can be complications. Large breeds and obese patients have a higher incidence of postoperative problems (prolonged recovery, secondary arthritis, etc.). Chondroprotective medications and weight management can help minimize these problems.

ACL Rupture

Normal Stifle

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