Dog wearing cast on leg
Cruciate ligaments are a group of ligaments inside each of your dog’s knees. When functioning properly, they stop the knees from twisting or overextending. But when the ligaments become injured, it can be very painful for your dog — many dogs even refuse to walk on the injured leg. (Dogs and cats both have cruciate ligaments, but most of the cruciate ligament injuries veterinarians see are in dogs.)

Why Does This Happen?

As a dog ages, cruciate ligaments can degenerate, resulting in a weakened and unstable joint; if this condition is not corrected, the ligaments can then tear (or rupture) during normal, everyday activities, including walking. Arthritis (osteoarthritis) or other abnormalities in the knee joint can also place unusual stress on the cruciate ligaments. Over time, this stress weakens the ligaments and can cause them to tear more easily. In younger animals, activities such as jumping or turning sharply (as when playing Frisbee) can also cause cruciate ligament injuries, even if the ligaments are healthy. Dogs who are overweight (regardless of age) are strongly believed to have an increased risk for cruciate ligament injury, so weight loss is usually recommended to help prevent the condition.

How Is the Problem Diagnosed?

Your veterinarian will start by performing a physical examination and obtaining a thorough medical history from you. Make sure you mention whether your dog has any other medical or orthopedic problems.

In many cases, sedation is recommended for an orthopedic examination and other diagnostic tests. Sedation provides muscle relaxation that can make subtle physical examination findings easier to detect. For dogs who are in a lot of pain, sedation may be the only way a safe and thorough examination can be accomplished.

During the physical examination, your veterinarian will feel (or palpate) your dog’s knee. By palpating the knee in a certain way, your veterinarian may be able to tell if the cruciate ligaments are no longer keeping the knee as stable as it should be. Diagnosis is frequently confirmed by taking X-rays.

Arthroscopy is often used to diagnose a cruciate ligament rupture and evaluate the menisci (disks of cartilage that help function as cushion between the bones in the knee joints, menisci are frequently damaged when there is a cruciate ligament rupture). Arthroscopy requires anesthesia and involves inserting a fiber-optic telescope (with a camera inside) through a very small skin incision and into the knee joint. Through a video monitor, the surgeon can see the cruciate ligaments and menisci inside the knee and determine the nature and extent of the damage.

How Is the Problem Treated?

Your veterinarian will consider several factors when deciding how to best treat your dog’s cruciate ligament injury. These include the severity and duration of the injury and your dog’s age, size and body condition (overweight versus normal weight). Small dogs (those less than about 30 pounds) can sometimes do relatively well without surgery. Controlled rest, medication and sometimes physical therapy can help these smaller patients. However, in general, surgery is recommended for dogs larger than about 30 pounds.

What Is the Prognosis?

In general, most dogs recover well after cruciate ligament injury if the condition is managed appropriately — even Sporting and Working dogs can often return to their previous lifestyles. 

However, because there is often an underlying problem that contributed to the cruciate injury (like osteoarthritis), approximately 50 percent of dogs will suffer a cruciate ligament rupture in the opposite knee within two years. Therefore, it can be beneficial to have both knees examined at the time of initial evaluation and institute weight management and other measures to help slow the progression of osteoarthritis. Your veterinarian will work with you to come up with an appropriate treatment and management plan.

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