Some studies suggest that if one CCL tears there's a 60% chance (or more) that the opposite side could tear. Does it depend on the breed? Definitely. Breeds most prone to CCL tears are Rottweilers, Newfoundlands and Staffordshire Terriers. Does gender play a role? Yes, females have a higher prevalence of tears. Can it be caused by the dog over-using the opposite hind leg when the other is injured? It makes sense to me. Does it have to do with spaying/neutering? Yes; studies show that spayed or neutered dogs are more likely to have CCL tears. And even though some studies say there is a correlation between a steep tibial plateau angle (TPA) and its relation to CCL tear, some don't show a correlation.
No matter the cause of your dog's CCL tear/s, let's review the anatomy of the hind leg.
Consider the dog's tibia (shin bone) and femur (thigh bone). In certain breeds, the top of the tibia (tibial plateau) is steep and angulated with the front of the tibia being the high side and the back being the lower side. Think of it like a street that has a steep hill.
The femur sits above the tibia and every time the dog performs the movements listed below, biomechanical stress is placed on the CCL.
Envision the steep street again, this time with some ice on it. Imagine a car parked on the incline with its hood pointing to the hill's apex. Under the car is a cable that attaches it to the street. The street is your dog's steep tibial plateau. The car is the femur, and the cable is the CCL. As the car slides backward down hill, it stresses the cable which then begins to weaken and fray. A similar set of events is happening to your dog's CCL.
Because the CCL attaches to the femur and tibia, the repetitive front to back shearing action between these bones causes the degenerative tear process to begin. As the CCL frays or tears completely, the tibia excessively shifts forward (tibial thrust) and the femur excessively slips backward. The result is pain, limping, swelling and eventual osteoarthritis.
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QUESTION: If your dog has bilateral CCL tears, how many months or years did it take before the second side tore? Please comment below.