What is the cruciate ligament?

There are two cruciate ligaments in the knee and they cross each other as they pass between the two main bones of the leg, the femur and tibia. If the knee is subjected to twisting when under load, a common injury is a tearing of the anterior cruciate ligament. The tear may be partial or complete and results in destabilization of the knee joint.

What causes cruciate ligament rupture?

Trauma to the knee joint may result in injury, but that is not a common cause in dogs. Often cruciate ligament rupture is a gradual process, resulting from chronic inflammation in the knee joint. Age-related changes, poor conformation, obesity, and immune-mediated diseases are some of the more common causes. An immune-mediated disease is a condition where the body’s defense mechanism turns against itself and starts attacking the body, instead of protecting it.

What are the signs of cruciate ligament rupture?

Athletic or traumatic events generally cause the kind of acute cruciate ligament injuries that result in a non-weightbearing lameness with the affected limb held up off the ground. Degenerative types of cruciate ligament injuries are noted by subtle to marked intermittent lameness that goes on for weeks to months. Bilateral disease, where both knee joints are affected, is common.

Cruciate lameness

Anterior drawer

How is a torn cruciate ligament diagnosed?

Your veterinarian may suspect cruciate ligament rupture after an examination. Without the stabilizing action of the anterior cruciate ligament, the femur and tibia move in an abnormal fashion in relation to each other. This instability can be demonstrated by eliciting the ‘drawer sign’. It can sometimes be demonstrated when the dog is conscious, but in many cases, the dog requires sedation or general anaesthesia to allow proper examination of the joint.

X-rays assist in identifying arthritic changes within and around the knee joint.

How is the problem treated?

Surgery to stabilize the knee joint is the best option for treatment. When the joint is unstable for a period of time, arthritic changes will begin that cannot be reversed. Some small dogs will respond to conservative treatment (i.e. without surgery) although the risk of developing degenerative joint disease is higher.

There are a few different techniques for this surgery, with new procedures continually being developed. This is to try to increase the success rate of the surgery so that the joint functions normally or near normally. Arthritis can still develop in the affected joint following surgery, but will be to a significantly lesser extent than if no surgery were performed.

Will the cruciate ligament in the other leg rupture also?

Overweight dogs are more prone to cruciate ligament tears, so a weight loss program is recommended for overweight dogs. In some cases, there may be degenerative changes in the ligaments that predispose them to injury, resulting in partial tears that can progress with time to full tears, so there is a chance that the opposite knee joint may have a similar type injury in the future. The underlying reason for these degenerative changes is not fully understood.

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