Mention torn ligaments and most people are more likely to think of athletes than animals. However, this problem also occurs in many pets and livestock. In fact, one of the most common knee injuries in dogs is known as a ruptured cruciate ligament.

The knee joint consists of three bones. The femur, or thigh bone, is the long bone that connects the hip to the knee. The tibia is the bone between the knee and ankle, and both of these bones are connected to the patella (kneecap) by a number of ligaments. Two of these ligaments crisscross, extending from the femur to the tibia, and are known as the cruciate ligaments. Their job is to prevent the ends of the femur and tibia from rubbing back and forth against each other. The ligament in front of the leg is called the anterior cruciate ligament (ACL to sports aficionados), while the one crossing behind the joint is the posterior cruciate ligament.

Injuries often cause these ligaments to rupture, usually when the dog twists on its hind leg, putting too much tension on the ligament. Often they are caused when a dog slips, makes a sudden turn while running or is struck by a car. Overweight dogs are particularly vulnerable, since their extra pounds can place too much stress on the knee joints.

When a cruciate ligament is ruptured, the dog will suddenly appear lame and usually will hold the affected leg off the ground. The knee also may become swollen. The dog may eventually begin using its leg again, but the lameness will reappear sporadically. Your veterinarian will diagnose a torn ligament through a physical examination of the knee and leg. In some cases, the dog may be sedated to better facilitate this exam.

Most torn ligaments end up requiring surgical treatment, especially in large-breed dogs. When the ACL is torn, there are several methods of surgical repair, all of which use synthetic suture materials and/or some of the knee joint's own fibrous tissue to re-create the ligament. The veterinary surgeon will attach this re-created ligament in the proper position to stabilize the femur and tibia. Following surgery the dog must be kept confined and as immobile as possible for at least two weeks. Then, after the initial recovery period, most dogs will heal completely within four to six weeks, if their movements are supervised and they are carefully exercised. In order for the joint to heal properly it must be exercised very gently, usually through short walks on a leash, in order to prevent the surgical correction from tearing. That's why it's important to follow your veterinarian's post-op instructions to the letter. The good news is that if these precautions are taken, most dogs recover from torn ligaments with no lasting ill effects.