Found in every joint of the body, ligaments are bands of tough, fibrous tissue that hold two or more bones in proper position. One of the ligaments that stabilizes the knee joint when the leg bends and moves is called the cranial cruciate ligament. When this cruciate ligament becomes loose, it is no longer able to ensure stable movement, and damage to the cartilage in the knee joint, leading to arthritis.
Ligaments are very strong tissues, but once they are damaged, they tend to heal slowly and incompletely. In people, cruciate ligament tears are often the result of rapidly occurring trauma, such as injuries resulting from skiing, football, soccer, and other sports accidents. Although this type of injury can also occur in dogs -- jumping up to catch a Frisbee, for example, can cause rapid trauma -- ruptured cranial cruciate ligament injury in the canine usually occurs progressively, over a period of time. There is often a partial tearing, which may show up as a low-level lameness and appears to improve in days to weeks. This partial tearing sets up inflammation within the knee joint, and the weakened ligament is further damaged with continued weight bearing. Eventually, this leads to complete rupture.
Due to a possible genetic component, some breeds, such as the rottweiller and cocker spaniel, are very prone to this disease. They may have some underlying genetic, conformational, or inflammatory disorder that predisposes the ligament to rupture; their susceptibility to the injury is a topic of research at many veterinary institutions. Obese animals are also at increased risk for this disease. However, dogs of all sizes and breeds can develop ruptured cranial cruciate ligaments.
Dogs with a ruptured cranial cruciate ligament in one knee have a 20 to 40 percent chance of injuring the other side, making a full recovery less likely.
