Dogs have two cruciate ligaments in each knee, giving them four cruciate ligaments total across their two back legs. The one equivalent to the human ACL is called the cranial cruciate ligament (CCL), and the second is the caudal cruciate ligament. Because dogs walk on four legs but only their hind legs have knee (stifle) joints, they don’t technically have an “ACL” at all. The term ACL is specific to human anatomy, though the CCL does the same job: preventing the shinbone from sliding forward under the thighbone.
Why Vets Say CCL Instead of ACL
“Cranial” means toward the head, and “anterior” means toward the front of the body. In humans standing upright, those directions happen to be the same for the knee, so the ligament is called the anterior cruciate ligament. In dogs, which walk on all fours, the equivalent direction is cranial. The American College of Veterinary Surgeons notes this directly: in humans the cranial cruciate ligament is called the ACL, but it’s the same structure in a different orientation.
The two cruciate ligaments in each stifle joint cross over each other (hence “cruciate,” from the Latin for cross). The cranial cruciate ligament prevents the tibia from shifting forward, while the caudal cruciate ligament prevents it from shifting backward. Together they keep the joint stable during every step.
Why Dogs Tear This Ligament So Often
Cranial cruciate ligament disease is the most common orthopedic condition in dogs, and the reason comes down to physics. The top of a dog’s shinbone (the tibial plateau) sits at a steeper angle than in humans. Every time a dog bears weight, that slope generates a forward-directed force called cranial tibial thrust, which the CCL has to absorb constantly. The steeper the angle, the greater the force.
This means the CCL in dogs doesn’t usually snap from a single traumatic event the way a human ACL tears during a soccer game. Instead, it wears down through repetitive microtrauma over months or years, weakening gradually until it partially or fully ruptures. A dog might be walking across the yard when the ligament finally gives way, even though the damage started long before that moment.
Breeds at Higher Risk
A large study from the Royal Veterinary College found that Rottweilers face 3.66 times the risk of CCL rupture compared to crossbreeds. Bichon Frises carry about twice the risk, followed by West Highland White Terriers at 1.8 times and Golden Retrievers at 1.69 times. Larger, heavier dogs generally put more load through their stifle joints, but the Bichon Frise’s presence on this list shows that genetics and ligament quality matter independently of size.
The Other Knee Is Often Next
One of the most important things to know about CCL injuries is that they frequently happen in both knees. In one study of Labrador Retrievers, 48% ruptured the CCL in the opposite leg within a median time of just 5.5 months. The same degenerative process that weakened the first ligament is typically already underway in the second. If your dog tears one CCL, there’s roughly a coin-flip chance the other knee will follow within the year.
How Vets Diagnose a Tear
Veterinarians use two hands-on tests to check for CCL damage. The cranial drawer test involves stabilizing the thighbone while pushing the shinbone forward. If the tibia slides and has a mushy, undefined endpoint rather than a crisp stop, the ligament is ruptured. The tibial compression test mimics weight-bearing by flexing the ankle while feeling for abnormal forward movement at the knee.
Partial tears can be trickier. A dog with only part of the ligament torn may show instability only when the knee is bent, not when it’s straight. Vets also check for pain when the knee is fully extended, swelling around the joint, and muscle loss in the affected leg. A clicking sensation during the exam suggests the meniscus (a cartilage pad inside the joint) has also been damaged.
Surgery vs. Conservative Management
Surgery significantly outperforms non-surgical management. A study comparing 615 surgical cases to 200 non-surgical cases found that surgery reduced short-term lameness by about 26 percentage points and long-term lameness by about 32 percentage points. Dogs managed without surgery can improve, but they’re substantially more likely to remain lame.
Three main surgical approaches exist. TPLO (tibial plateau leveling osteotomy) reshapes the top of the shinbone to eliminate that forward-sliding force, removing the need for a functioning CCL altogether. TTA (tibial tuberosity advancement) achieves the same mechanical result by repositioning where the kneecap tendon attaches. Both procedures work by changing the geometry of the joint so the bones are stable without the ligament. A third option, the lateral suture technique, uses a strong synthetic line outside the joint capsule to replace the ligament’s restraining function. This is more commonly used in smaller dogs.
As of 2025, TPLO surgery costs roughly $6,000 to $10,000 per leg. Given the high likelihood of bilateral injury, many owners end up facing this cost twice.
What Recovery Looks Like
Whether your dog has surgery or not, the first 8 to 12 weeks of rehabilitation follow the same basic pattern: no running, jumping, rough play, or sharp turns. For the first week after surgery, most dogs need an abdominal sling for support during short walks. Ice is applied for 20 to 30 minutes several times daily in the first few days to manage swelling.
Gentle range-of-motion exercises start immediately, with 10 to 15 repetitions two to three times per day for the first two weeks. By week two, dogs begin standing exercises that progressively challenge balance. Sit-to-stand exercises can start around three to five weeks depending on the type of surgery. The full rehabilitation timeline stretches well beyond that initial 8 to 12 week restriction period, with gradual return to normal activity over several months. Dogs with bilateral disease (both knees affected) need longer sling support, at least two weeks, and a more cautious progression overall.