Ruptured Cranial Cruciate Ligaments

Dear Dr. Jody:  Our six year old Rottweiler cross, “Tank”, has just been diagnosed with a torn cruciate ligament in his knee.  We have been told that he requires surgery to correct this injury, but he seems to be doing better on the pain medication.  Can we just wait and see if the pain medication solves the problem?

Torn cruciate ligaments are one of the most common orthopedic problems seen in our canine patients.   Most people have heard of ACL injuries in skiers and football players, and some of us have even experienced the injury ourselves.  In human patients, a torn ACL refers to a damaged anterior cruciate ligament.  In pets, we call the ligament a cranial cruciate ligament (CCL).

The CCL is a band of fibrous connective tissue that joins the top of the tibia with the bottom of the femur.  This ligament allows the knee to flex and extend, but it prevents the tibia from slipping forward of the femur; an unstable movement that would result in pain and buckling of the knee.

The CCL can be damaged in several different ways.  There are certain breeds that seem genetically predisposed to this injury, including Rottweilers, Newfoundlands, St. Bernards, and pitbulls.  With these larger breeds, sometimes the ligament will fray over time like a rope under too much strain.  At some point, the frayed ligament can suddenly snap, causing acute pain and severe lameness on that leg.  Dogs that are overweight or obese are at dramatically higher risk for developing a ruptured CCL.  Occasionally, the ligament will snap in a dog that is not obese if the dog is hit by a vehicle or if he suddenly turns quickly, causing increased rotational force on that knee.  Any injury that results in the knee twisting suddenly will put the CCL at great risk of rupture.

Your veterinarian can diagnose a ruptured CCL with a cranial drawer test.  In this test, the veterinarian holds the top of the tibia in one hand and the bottom of the femur in the other hand and tries to push the tibia forward and the femur backward.  A healthy ligament will not allow the tibia to move forward with respect to the femur, but abnormal movement in this regard is interpreted as a positive cranial drawer sign and confirms the diagnosis.  Often, sedation is required to be able to perform this test properly, and occasionally, the results of this test are equivocal.  Although the CCL does not show up on x-rays, your veterinarian will likely recommend x-rays to ensure that the hips are sound and that there are no degenerative changes within the knee joint itself. 

Unfortunately, because the torn ligament does not regrow, there is no cure for a ruptured CCL other than surgery.  There are at least three different surgeries that can be done to correct a ruptured CCL.  The most common is called an extracapsular repair.  In this surgery, a high tensile fishing line is used to stabilize the knee joint by replacing the torn CCL.  The surgeon will also inspect the meniscus, a cushion of cartilage that separates the tibia and femur.  This cartilage is often torn when a CCL is ruptured, and if it is damaged, the meniscus must be removed.  In another surgery known as a tibial plateau leveling osteotomy (TPLO), the surgeon makes a cut through the top of the tibia, rotates the cut bone a certain number of degrees, and screws it in place with a special metal plate.  The ligament itself is not replaced, but by changing the angle with which the top of the tibia meets the bottom of the femur, the knee is effectively stabilized.

Your veterinarian will determine which surgical method is best for your dog based on a number of different factors, such as your dog’s age, breed, degree of obesity, and long term activity expectation (whether you expect to jog or hike with your dog). 

Without surgical correction, the knee will always be painful and unstable.  The prognosis with surgery is extremely favorable, but unfortunately, a large percentage of dogs that injure one knee will go on to rupture the CCL in the other knee within the next 12 months, even if the bad knee is corrected.  We always prepare owners that there may be a second surgery on the horizon for their pet. 

If your pet has been diagnosed with a torn CCL or is demonstrating undiagnosed hind limb lameness, please discuss the treatment options with your veterinarian.  Surgically correcting this problem early on will give your pet the best chance possible for long term comfort.