Cruciate Ligament Tears and Dogs
Quick Facts from a Veterinarian
Jennifer Hawkins, DVM
“Cooper," a long-time patient of our animal hospital, had only just recovered from an abdominal surgery when he came limping into our hospital one Saturday.
According to his owner, he had limped a few weeks earlier and, just as his owner was about to bring him in, the limp seemed to resolve. However, the limp was clearly back and Cooper was favoring one of his rear legs.
While his tail wagged endlessly and he smiled when I spoke to him (yes, this dog did smile), he was clearly in pain as he would barely place weight on his injured rear leg. Sedation and X-rays, along with my orthopedic exam, confirmed what I had suspected...Cooper had torn a cruciate ligament in his knee.
What is a Cruciate Ligament?
Most of us have probably watched football replays of players tweaking a leg in an odd direction and limping off the field. The sports commentators later tell us that the injury resulted in a torn ACL. But, what is the ACL?
ACL stands for the anterior cruciate ligament which prevents forward thrusting of the tibia (shin bone) when walking. There are four ligaments in the knee, one in the front (the anterior cruciate ligament), one in the back (the posterior cruciate ligament), and one on each side (the collateral cruciate ligaments).
In dogs, instead of “anterior” cruciate ligament, we call it the cranial cruciate ligament or CCL. However, the terms ACL and CCL are often used interchangeably in veterinary medicine. These four ligaments maintain stability of this joint that receives so much stress from our dogs' very active lives. Tear of the CCL is one of the most common orthopedic injuries seen in veterinary medicine.
It’s important to note that a CCL rupture is almost always a degenerative condition of the anterior cruciate ligament and not the result of an acute trauma or injury to the knee as it is in humans. The degenerative process is thought to be the result of weight bearing forces necessary to control cranial tibial thrust and internal rotation of the tibia.
Hyperextension of the stifle joint is also a factor in the degenerative process and tear of the CCL.
In addition, there are also hereditary and developmental factors of limb conformation prevalent in some breeds that predispose to CCL rupture.
Are Some Dog Breeds More Prone to CCL Tear?
Large-breed athletic dogs such as German shepherds, Rottweilers, Labradors and golden retrievers are commonly seen with CCL tears. However, any sex, age or breed of dog may be affected, even small-breed dogs like Chihuahuas.
Veterinary studies show that up to 60 percent of dogs who tear one CCL will tear the opposite one in the following 1-2 years. Cats rarely acquire CCL tears.
What are the Symptoms of a CCL Tear?
Sometimes an owner witnesses their dog yelping or holding up a hind leg during exercise. More often, the injury is not witnessed, but pet owners notice that their dog is favoring a rear leg.
The lameness is typically intermittent and most obvious after mild or moderate exercise. The other ligaments in the knee do stabilize the knee somewhat after the dog has rested; however, once activity resumes, the lameness tends to recur.
How is a CCL Tear Diagnosed?
In addition to a thorough history and exam, X-rays are needed to rule out other causes of lameness and knee pain such as fractures, arthritis or cancer.
An orthopedic exam, in which your veterinarian manipulates all the joints of the leg, is performed and often requires sedation of the dog so that his muscles are relaxed sufficiently to permit evaluation. The history of acute or intermittent lameness, combined with knee instability and X-ray evidence of joint swelling, all are consistent with the diagnosis of CCL tear.
How is a CCL Tear Treated?
In the human field, people are sometimes able to avoid surgery and instead go through physical therapy to strengthen knee muscles while the ligament heals. Physical therapy, however, is not commonly a long-term option for a dog.
Take a moment and look at how your legs are vertical when you stand. Then, look at how your dog’s rear legs are angular when standing. Now stand on your tippy toes and bend your knees (don't fall!).
Look familiar? This is exactly how your dog stands on his hind legs. Can you see how he has a great deal of tension on his knees? Dogs simply aren't built the same way as people and thus typically require surgery to repair a torn cruciate ligament to limit long-term consequences such as pain, arthritis and decreased range of motion.
In the case of a minor tear, especially in small dogs, your veterinarian may first choose a conservative plan of rest and anti-inflammatory pain medication. It is important to know that, even though the symptoms may resolve, the instability is still present and secondary arthritis will likely develop in these dogs.
Methods of Surgical Repair of a Torn CCL
The goal in any CCL surgery is to decrease the instability of the knee joint caused by the tear. There are several surgical techniques to repairing a torn CCL in dogs.
Intracapsular repair (inside the knee joint) involves stabilizing the joint by replacing the ruptured ligament to its normal position or using a tissue graft to replace the ligament.
Extracapsular repair (outside the knee joint) may involve the use of suture or the dog's connective tissue to stabilize the joint.
Other extracapsular repair methods involve techniques that alter the geometry of the joint. The tibial plateau leveling osteotomy (TPLO) and the tibial tuberosity advancement (TTA) are both techniques in which the instability of the knee joint is remedied by altering the biomechanics of the knee itself.
This is done by actually cutting the tibia and adjusting the angle of the top fragment, then placing a bone plate or device to allow the bone to heal in a new position. It may sound unusual to cut the tibia in order to fix the knee, but the resulting improvement in the knee stability leads to a speedier return to normal gait and less long-term arthritis in the knee.
The decision as to which technique is most appropriate for your dog may depend on the size of your dog, the severity of the tear and associated joint changes, as well as the surgeon's preference.
How Long is the Recovery Time for a CCL?
Depending on the dog, severity of injury and method of repair, it may take six to 12 weeks to return to normal function.
During that time, you may be asked to keep your dog rested and limit outside activity to controlled short-leash walks only. It is helpful initially to use a towel or sling under your dog's hips to support his weight while he recovers from his surgery.
Our patient Cooper was an excellent candidate for the TPLO procedure. His procedure was performed by a boarded veterinary surgeon within a few days of his diagnosis.
Cooper recovered well and actually insisted on walking on the injured leg immediately after recovery from anesthesia! This smiling dog seemed to feel so much better that we had to work hard to curb his activity while he healed. In one month he was nearly completely healed and by two months, he was back to all his normal activities.
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Dr. Hawkins received her veterinary degree from the University of California, Davis and practices in Orange County, Calif., where she also works at local animal shelters. In addition, she is an advisory faculty member for aspiring veterinary technologists at California State Polytechnic University Pomona. Dr. Hawkins is an active member of the Southern California Veterinary Medical Association where she serves on the Board of Trustees.
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