Understanding Cruciate Ligament Injuries

Cruciate ligaments are a group of ligaments inside the knee. When functioning properly, they stop the knee from twisting or overextending. However, the ligaments can degenerate (especially in older dogs), resulting in a weakened and unstable joint; if this condition is not corrected, the ligaments will usually tear (or rupture). Activities such as jumping or turning sharply (as when playing Frisbee) are a less common cause of cruciate ligament injuries and more likely to occur in younger animals.

Regardless of what causes the condition, this type of injury is typically very painful, and many dogs 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?
In some cases, a dog with a normal knee can tear his cruciate ligament during strenuous activity. However, if the knee ligaments have degenerated, the risk of injury during normal activities can increase. For example, arthritis or an unstable kneecap can place unusual stress on the cruciate ligaments. Over time, this stress weakens the ligaments and can cause them to tear more easily. Dogs that are overweight 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 that 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 By Karen Todd-Jenkins, VMD Understanding Cruciate Ligament Injuries 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 function as a cushion between the bones in the knee joint, menisci are frequently damaged when there is a cruciate ligament rupture.) Arthroscopy requires anesthesia and involves inserting a fiberoptic 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 with six to eight weeks of rest followed by physical therapy and rehabilitation without the need for surgery. However, in general, surgery is recommended for dogs larger than about 30 pounds.

There are several options for treating cruciate ligament ruptures; all involve two general steps:

• First, the cruciate ligaments and menisci need to be evaluated either through a skin incision or through arthroscopy. Because the surgeon already has access to the joint structures during an exploratory arthroscopy, treatment of a damaged meniscus and removal of the degenerative cruciate ligament can be provided immediately. 
• Next, the knee can be stabilized surgically if necessary. Two general categories of procedures are performed: Sutures are placed under the skin and muscles to provide stability, or the surrounding bone structures are reconfigured to help stabilize the joint.

WHAT IS THE PROGNOSIS?
In general, most dogs (around 90%) recover well after cruciate ligament injury if the condition is managed appropriately. According to Samuel Franklin, DVM, at the University of Missouri College of Veterinary Medicine in Columbia, even sporting and working dogs can return to their previous lifestyles. He notes, however, that “the overwhelming majority of dogs, including those who make an excellent recovery, tend to suffer from osteoarthritis, which may become worse over time.” He recommends weight control, moderate exercise, and appropriate joint support supplements to slow progression of long-term arthritic changes.

Unfortunately, because there is often an underlying problem that contributed to the cruciate injury, approximately 50% of dogs will suffer a cruciate ligament rupture in the opposite knee within two years. Therefore, Dr. Franklin recommends having both knees examined at the time of initial evaluation and instituting weight management and other measures to slow the progression of osteoarthritis. Your veterinarian will work with you to come up with an appropriate treatment and management plan for this type of injury.

For more information on cruciate injuries, please see this article in our Musculo-Skeletal Center.