How rupture occurs
Several clinical pictures are seen with ruptured cruciate ligaments. One is a young athletic dog playing
roughly who takes a bad step and injures the knee. This is usually a sudden lameness in a young dog.
On the other hand, a middle aged or older dog, especially if overweight, can have weakened ligaments and slowly stretch or partially tear them. In this type of patient, stepping down off the bed or a small jump can be all it takes to break the ligament.
As often the underlying reason for the tear is a gradual weakening of the cruciate ligaments, the problem often occurs in the other hind leg's knee joint as well within a few months to a year or two. Owners therefore should be prepared for the possibility of another surgery in this time frame.
The ruptured cruciate ligament is the most common knee injury of dogs; in fact, chances are that any dog with sudden rear leg lameness has a ruptured anterior cruciate ligament rather than something else. The history usually involves a rear leg suddenly so sore that the dog can hardly bear weight on it. If left alone, it will appear to improve over the course of a week or two but the knee will be notably swollen and arthritis will set in over time.
What Happens if the Cruciate
Rupture is Not Surgically Repaired?
Without an intact cruciate ligament, the knee is unstable. Wear between the bones and meniscal cartilage becomes abnormal and the joint begins to develop degenerative changes (arthritis of the knee). Bone spurs called osteophytes develop resulting in chronic pain and loss of full joint motion. This process can be arrested or slowed by surgery but cannot be reversed.
What Happens - Surgical Repair
Due to the cruciate ligament being damaged, the knee is no longer able to support weight when walking and standing. As the ligament is ruptured or weak, it cannot be repaired. To correct the problem we change the slope of the knee and the ligament is no longer necessary for support.