Cruciate ligament injuries in Labradors

The dog's knee is similar to a human knee, in terms of joint function and orthopedic condition. A dog's joint consists of various parts: Femur (thigh bone), tibia (shin bone) and patella and supporting ligaments and tendons. The cranial cruciate ligament (CCL) is connected to the femur, extends across the stifle joint, and attaches to the tibia. The CCL holds the tibia in place and prevents internal rotation and hyperextension. The cranial cruciate ligament (CCL) (also known as the anterior cruciate ligament or ACL in humans) is the most commonly ruptured ligament in dogs. The rupture results in lameness due to pain and instability of the joint. When the cruciate ligament is torn the femur slides down the sloped top portion of the tibia called the tibial plateau. The misaligned joint as result of CCL causes inflammation, pain, and eventually degenerative joint disease.

The Labrador is one of the predisposed breeds, along with the Rottweiler and Newfoundland. The greyhound is a breed that seems “protected” from CCL disease. It generally occurs from 1-8 years of age in either sex, with obesity being a primary factor.

We know that in dogs, CCLs rupture as part of a degenerative process within the stifle joint but we don’t have a good understanding of the pathophysiology involved. Researchers at the University of Liverpool provided a small glimpse into this disease process by making comparisons between Labrador retrievers, as an example of a breed prone to CCL rupture, and greyhounds, as an example of a breed at the opposite end of the spectrum. They demonstrated that the collagen fibril diameter in the CCLs of Labradors is significantly smaller. The researchers also showed that the tissue concentrations of matrix metalloproteinase 2 (MMP-2), the major degradative enzyme found in the stifle, are higher and the levels of tissue inhibitors of MMP-2 are lower in affected Labradors.

These findings represent an increased degree of “collagen turnover” in these dogs, but whether that is a cause or a result of their “cruciate disease” has yet to be determined. In addition, statistical gait analysis comparisons of normal individuals from these 2 breeds have been initiated, and although consistent differences have been documented, their significance, as it pertains to the development of cruciate disease, has yet to be determined.

The cause of cranial cruciate ligament rupture is not known for certain, but hereditary or genetics likely a factor. Risk factors associated to CCL include age, injury to stifle joint, being overweight, arthritis, poor musculature near the joint and structural abnormalities including cow-hocked and luxated patella. A rupture of the cranial cruciate ligament usually occurs when a dog steps in a hole while running or turns with its paws remaining planted. As the ligament is twisted, it is rotated extensively or hyperextended and partial or complete rupture occurs.

Here is a summation article on Dealing with Cruciate Ligament Injuries in Labradors.