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The cranial cruciate ligament (CrCL) tear is the most common orthopedic injury in dogs. This ligament is synonymous with the “ACL” in humans. In humans, the front of the body is called “anterior;” in dogs, the front is called “cranial.” In both species, the ligament is inside the front of the knee joint and is a primary stabilizer of the knee. CrCL tears in dogs, however, typically occur due to different reasons than ACL injuries do in humans. The focus here is on why these injuries occur in dogs and on how we use TPLO surgery for CrCL tears.
How CrCL Tears in Dogs Are Different from ACL Injuries in Humans
In a human being, an ACL tear is typically a trauma-based injury. For example, a football player might take a hit or a quick turn and sustain a tear. In dogs, the CrCL tear is due to a degenerative process occurring in the ligament. This leads to weakness and small tears over time. Eventually, an everyday activity like stepping down from a couch or trotting around the yard leads to a significant tear.
There are various hypotheses for this degenerative process in dogs. What we do know is that the anatomy of the canine knee involves a steep angle at the level of the top of the tibia (shin bone). This steep angle called the “tibial plateau,” allows the bottom of the femur (thigh bone) to slide down that slope and push the tibia forward. This, in turn, leads to stretching and straining of the ligament with each step the pet takes. Over time, the weakened ligament tears, leading to a forward/backward shift of the joint as the pet bears weight. The result is pain and inflammation with progressive arthritis.
TPLO Surgery for CrCL Tears
The physical differences between the human and the dog make the surgical recommendations significantly different. In humans, an orthopedic surgeon will often replace the torn ligament with a graft. In dogs, this same approach would set the patient up for a future tear. This is because the anatomy of the joint is what caused the injury to begin with. Without altering the anatomy, we cannot permanently stabilize the joint or prevent future CrCL tears. Dogs bear 70% of their weight on their forelimbs (arms). They have different weight-bearing forces when walking than humans do. For this reason, we do not aim to replace the torn ligament. Rather, we reorient the joint so that the dog no longer needs the CrCL. This is the permanent repair/stabilization that we desire.
To reorient the joint, we often recommend a Tibial Plateau Leveling Osteotomy (TPLO). This procedure involves an osteotomy (cut of the bone) of the top of the tibia with rotation of the plateau to make it flat. Using TPLO surgery for CrCL tears prevents the femur from sliding off the back of the tibia, thus stabilizing the joint without the need for a CrCL to be present. Once the bone has been cut and rotated, it must be held in place with a plate and screws so that the bone can permanently heal in that orientation over 8-10 weeks.
Recovery From TPLO Surgery
After the bone has healed, the pet can run/jump/play with a stable joint and will never risk another tear in that same leg. It is important to note, however, that CrCL tears are anatomy-based injuries, and anatomy tends to be symmetrical. About 60% of dogs will at some point in their lives tear the CrCL in the other knee. Unfortunately, there is little that can be done to prevent a tear in the “good” knee aside from keeping the pet at a lean body weight and stabilizing the “bad” knee to allow them to get back to bearing normal weight on both legs so as not to overload the “good” leg.
The TPLO surgery requires 8 weeks of activity restriction (no off-leash running/playing), with the first 2 weeks also requiring an E collar or “cone” to prevent the pet from licking the incision. After the healing process, we will take x-rays to confirm bone healing. Then the pet can return to normal activity incrementally.
Prognosis
The prognosis for return to function after TPLO surgery for CrCL tears is excellent in most dogs, allowing them to resume normal activity long-term. It is important to note, however, that the instability incurred by the injury does result in arthritis. The longer we don’t treat that instability, the more arthritis and lameness the pet risks even after surgical repair.
An ACVS-boarded surgeon should perform TPLO surgery. Charlotte Animal Referral and Emergency has 3 boarded surgeons who are well-versed in this procedure. For more information and diagrams, please visit the CrCL page on the American College of Veterinary Surgeons website.
Charlotte Animal Referral and Emergency operates as the pet equivalent of a human medical center. CARE offers all types of treatments, from emergency care 24 hours a day and 365 days a year to board-certified specialty attention once you get a referral from your primary veterinarian. We hope you’ll take a visual tour of the practice at carecharlotte.com/tour.
