What’s a Cranial Cruciate Ligament (CCL) Injury?
What it is, why it happens, and how we diagnose it.
If your dog or cat can’t put weight on a hind leg, your pet may have a painful CCL injury. The good news: you can help your pet lose the limp and become active once again.
What is a CCL Injury?
A Cranial Cruciate Ligament (CCL) injury in a dog or cat is similar to an Anterior Cruciate Ligament (ACL) injury in a human. Looking at the animal’s hind leg, the Cranial Cruciate Ligament is located within the knee joint and connects the upper long-bone (the femur), to the lower leg bone (the tibia).
The knee is a complex structure with four ligaments that allow flexion and extension while maintaining stability along the long axis of the two long bones. When the Cranial Cruciate ligament is torn, the tibia shifts forward when the femur is bearing weight. This causes the knee joint to become unstable (and painful!). An animal with an injured CCL will limp to avoid putting weight on the knee joint. lameness. Ligament injury can occur to varying degrees: the ligament can be strained, sprained, partially torn, or completely ruptured.
Strain: The ligament has been stressed to the point of pain, but not beyond its elastic limit. There is no tissue damage.
Sprain: The ligament has been stressed beyond its elastic limit and the tissue is damaged, but not to the extent of a tear.
Partial tear: The CCL is composed of two parts: a strong, nonelastic cable and a weaker, stretchier portion. When the CCL is partially torn, the stretchy portion may tear partially or completely, but the strong cable portion is still intact.
Complete rupture: The ligament is completely torn in half.
Regardless of the type of CCL injury, all degrees of ligament damage cause painful, non-weight-bearing lameness. Immediate veterinary care is essential. Left untreated, a strained or sprained ligament may advance to a torn or ruptured CCL.
How do CCL injuries occur?
Certain dog breeds have a higher incidence of CCL injuries. These breeds include: Rottweiler, Newfoundland, Staffordshire Terrier, Mastiff, Akita, Saint Bernard, Chesapeake Bay Retriever and Labrador Retriever. Bow-legged animals are also more prone to CCL injuries.
Cranial Cruciate Ligament (CCL) injuries are caused in one of three ways:
Trauma: any animal with a knee joint can sustain trauma to the hind leg sufficient to injure the CCL.
Inflammatory Deterioration: Chronic inflammation within the knee joint causes a deterioration and weakening of the CCL which can lead to ligament failure. Some dog breeds are pre-disposed to inflamed knee joints—but this condition can also develop in chronically-overweight small to medium-size dogs. Dogs with an anatomic defect such as Luxating Patella can also develop inflammation in the knee. Inflammatory deterioration is most common in older pets.
Anatomical Flaws: Certain animals have a flaw, from birth, in the anatomic structure of the knee joint. When there is an excessive angle to the weight-bearing surface of the tibia (Tibial Plateau), it puts an excessive load on the ligament. This causes ligament failure (such as a tear) at a young age. Certain breeds and conformations are more prone to this type of injury.
Types of CCL injuries
Progressive CCL Injury
For many pets, CCL injury begins with a sprain. An animal’s lameness may resolve with anti-inflammatory medication and rest (two months minimum), but then the sprain recurs once activity resumes. This cycle may repeat itself until the sprain progresses to a partial tear, then to a complete tear. Animals that continually re-injure their Cranial Cruciate Ligament can suffer three serious health consequences:
Their thigh muscles can atrophy.
Their knee joint can develop arthritis from the unnatural grinding together of the tibia and femur.
Their CCL can become increasingly damaged.
Acute CCL Injury
Acute injury—resulting from sudden trauma—is also common. Owners often describe their pet suddenly crying out during high-impact activity, such as sprinting, rapidly turning or jumping, then coming up three-legged lame. Older, obese pets can injure the CCL by simply jumping off the couch.
How is a CCL injury diagnosed?
Your pet’s age, fitness, skeletal conformation and breed, as well as the degree of lameness, and past history of the injury/lameness, can serve as indicators of CCL damage.
At High Desert Veterinary, we evaluate the CCL using three tests:
Sit Test: We ask your pet to sit, and we observe the resting position of the hind legs. Pain or instability of the knee will cause an animal to extend the injured leg out to the side or underneath the body. Dogs and cats with a CCL injury can’t tolerate sitting with both hind legs squarely underneath.
Drawer Test: We hold the end of the Femur at the knee joint in place and then gently push the knee-end of the tibia toward the animal’s head (as if opening a drawer). If this manipulation is painful, or if the range of the tibia is excessive, we can tell the knee is injured. This test is best performed under sedation.
Cranial Tibial Thrust (CTT): We grasp the knee-end of the femur with a thumb and middle finger, allowing the index finger to rest on the cranial tip of the tibia. We extend the leg into a weight-bearing position and flex the hock (ankle) joint. If the CCL has a tear, our index finger will move toward the animal’s head. If this manipulation feels painful to the animals, it indicates a strain or sprain to the CCL.
A thorough orthopedic exam is necessary to diagnose a CCL injury and rule out injury to the other joints, muscles, tendons, ligaments and bones of the hind leg. While torn CCLs are more obvious, it takes skill and experience to identify an early or mild CCL injury and determine if the injury is a strain, sprain or partial tear.