Knee Injuries:
Cruciate Ligament in Dogs
By Dr. Colleen Skavinsky, Chief Veterinary Officer

The stifle, also known as the knee joint, is truly a wonder of bio-mechanical engineering. The thigh bone (femur) is connected to the shin bone (tibia and fibula) by a number of tendons and ligaments, including the cruciate ligaments. The bones are separated by two little cartilage cushions known as the menisci (singular form-meniscus). The cruciate (cross) ligaments inside the stifle help to stabilize and coordinate the hind leg during normal motion. The cranial cruciate ligament (CCL) is equivalent to the anterior cruciate ligament (ACL) in humans. Cranial cruciate ligament injuries are one of the most common orthopedic conditions we see in dogs.
There are a number of factors involved in the development of cranial cruciate problems. Dogs appear to injure the cruciate ligament during activity. The normal stabilizing mechanisms within the knee are strained by sudden twists or turns to the point of partial tearing or true rupture. Playing with Kongs or other toys that bounce at unpredictable angles may cause this type of strain. Dogs who slip on stairs, trip in gopher holes, or slip on ice are at risk for knee injuries.
Actual trauma, however, actually accounts for a minority of ligament ruptures in dogs. More commonly, a degenerative process weakens the ligament over time until it eventually tears and ruptures. Progressive degeneration of the ligament has been attributed to a variety of factors. Dogs who are obese and inactive are four times more likely to rupture the cranial cruciate ligament. Conformation can play a role in dogs who do not possess normal angulation in the joints of the hind leg. Certain breeds may have a genetic predisposition to cruciate injuries: Rottweiler, Labrador Retriever, Newfoundland, and Boxer. The disease process in affected breeds may explain why these dogs have a 40 to 60% chance of tearing the cruciate ligament in the other leg within two years.
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