Cranial cruciate ligament ruptures (CCL) are the most common stifle problem in dogs. CCL is also common in Australian Shepherds. The cruciate ligament stabilizes the stifle joint by keeping the femur (thigh bone) and tibia (major leg bone below the stifle) in proper orientation. Ruptures occur due to ligament degradation over time. A wide variety of factors play a role in this, probably including some degree of heredity. Affected dogs exhibit lameness in the affected leg and an unstable gait. CCL can be extremely painful and requires treatment. In a dog the size of an Aussie, surgery is necessary to stabilize the joint. If surgery cannot be done for some reason, a knee brace may help. This is a career-ending injury in a working or performance dog.
If multiple cases have occurred in a group of related dogs, affected dogs should not be bred. Their first-step relatives (parents, offspring, full and half siblings) should be bred only to mates with no recent family history of CCL.