The Leg Angle & CCL Injuries in Dogs

The cranial cruciate ligament, or CCL, corresponds to the anterior cruciate ligament, the ACL, in humans. Injuries to the CCL are common, particularly in very young and athletic dogs or in older, overweight dogs. The angle of the dog’s leg along the top of the tibia is thought to contribute to CCL injuries, although other factors can contribute to ruptures and tears of that ligament.

The tibial plateau angle sometimes causes instability in the dog’s knee joint, causing ruptures or tears to the CCL. This angle is formed by the relative positions of the shaft of the tibia and the top of the tibia. Steep tibial plateau angles cause strain on the ligament, increasing the possibility of damage. However, dogs with normal angles may also experience ligament damage -- so age, weight, and activity must also be considered factors in gauging the possibility of damage.

Many factors can contribute to CCL damage. Two major factors include degeneration of the ligament over time, and trauma experienced during activities such as jumping and running. Degenerative damage may occur due to the dog’s weight or due to other diseases or disorders. For example, hip dysplasia can cause degeneration by forcing the dog to compensate for weakness in one part of his body, for instance the hips, by using another part of his body, such as the knees, to support the joint. Hyperextending the leg, falling, twisting or wrenching the joint can cause traumatic injury. In part, these injuries can be caused by owners asking overweight or out-of-shape dogs to engage in strenuous or prolonged activity. Because a dog’s knee is always flexed or bent, his knees are always bearing some kind of weight. The greater the angle, the greater the stress on the dog’s knees.

CCL injuries can be diagnosed by observing typical symptoms of swelling, tenderness and sudden lameness. Such lameness is characterized by the dog holding the affected leg above the ground as he walks or trots. CCL injuries are also diagnosed using X-rays or a procedure called the cranial drawer test. This test consists of the veterinarian attempting to slide the end of the femur across the top of the tibia. These two long bones form the angle of the knee. The anterior or front cruciate ligament and the caudal or rear cruciate ligament cross one another to support the knee joint. If either ligament has been ruptured or torn, the two bones of the joint move independently in a motion that approximates the opening of a drawer.

Partial CCL tears can be treated by rest and medical treatment of the symptoms. Complete tears and ruptures of the CCL are often treated with surgery. Small dogs are treatable by strengthening the joint by using strong sutures to create an artificial ligament. This procedure is less effective for larger dogs. Other surgical treatment methods involve removing the tibial head from the end of the bone and repositioning it to reduce the joint angle and strengthen the leg.