Like humans, animals are susceptible to tears in the connective tissue that stabilizes joints. Dogs are particularly prone to a condition known as cranial cruciate rupture, or a tear in the anterior cruciate ligament of the stifle joint. This joint, located between the femur and lower leg bones, functions as an equivalent to the knee in humans.
Rupture of the cranial or anterior cruciate ligament contributes to most cases of lameness in a dog's rear leg. Also a common cause of degenerative disease of the stifle joint, it is particularly common in spayed females and in dogs older than five years. Certain large breeds, including Labradors and German shepherds, are also particularly susceptible to a CCL injury, as are those who are obese or who engage in sporadic intense exercise. Furthermore, if a dog does present with a torn CCL, he or she has a 50 percent chance of experiencing a similar injury in the opposite rear leg.