Some ACL injuries are traumatic from either the dog’s leg being hit by another dog or object or from the dog running and stepping in a hole. When traumas occur they force the lower leg or Tibia forward on the upper leg thus putting this ligament under stress The dog however in many cases is predisposed to this injury because of the angle at its knee joint. If you look at a dog’s leg it is not completely straight as a human’s leg. A Dog’s legs are bent at the knee, some dog breeds more than others. This creates far more stress and strain on the Anterior Cruciate ligament. Because of the angle of its attachments and so wear and tear can be a common factor in its injury. Certain breeds are more disposed to this injury such as Labrador Retrievers, Mastiffs and Newfoundlands, Rottweilers and Golden Retrievers to name a few. These are also large dogs that carry a great deal of weight. Small dogs incur this injury although it is not as common. Just as any other structure when enough tension or wear and tear occurs to the Anterior Cruciate Ligament it may fail. Weight and age will predispose a dog to an increased incidence of this injury as well as diminishing successful treatment. Ligaments in general, including the Anterior Cruciate may have many levels of injury to them. They might have a strain which means it has been pulled to the extent of irritation and inflammation but not torn. It might a small tear or it might have a complete tear and anything in between. Very often, perhaps up to 90 percent of these injuries have associated meniscus tears. Think of the Meniscus as two separate rings of a stiff form of cartilage which go around the periphery of both sides of the knee or stifle joint.. These rings deepen the joint to make it more stable These structures can tear and fray which when the ACL ligament is injured. In most cases these can heal on their own if stresses to these areas are kept to a minimum.