Cranial Cruciate Ligament (CCL) rupture is one of the most common veterinary orthopedic injuries in dogs and causes intense pain, swelling and lameness in one or both hind legs.

With an acute (sudden) rupture of the cranial cruciate ligament many dogs will not place weight on the leg at all, sometimes leading owners to believe the leg has been broken or fractured. The cranial cruciate ligament is inside the knee, analogous to the ACL (anterior cruciate ligament) in humans, that prevents abnormal rotation and forward and backward motion of the bones of the knee relative to each other. In humans, these ligament tears are almost always traumatic – they occur when a soccer player twists a knee, a skier takes a bad fall, or a football player gets tackled. 

In dogs, CCL injuries are usually not associated with significant trauma. In humans, the top of the shin bone is essentially flat, so we only put strain on our cruciate ligament if we pivot our knee excessively or suffer a blow to the top of our shin.  In dogs, however, the top of their shin bone is angled an average of 25 degrees. This means that any time a dog is standing, walking, or putting weight on their leg, gravity wants the bottom of the thigh bone to slide backwards down that slope, like a car parked on a steep hill. This constant strain on the dog’s cruciate ligament predisposes them to a more chronic, gradual fraying of the fibers of the ligament that can lead to a complete tear over time.

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