Anterior Cruciate Rupture

Filed Under: Dogs, Orthopedic

Is your dog suddenly hopping on one rear leg? Is your dog overweight? Was your pet neutered or spayed before 6 months of age? Then your pet may be suffering from anterior or cranial cruciate rupture. The AVMA estimates that pet owners spend over $1.32 billion yearly for the repair of rupture anterior cruciate ligaments on their pets.

The stifle or knee joint is actually a hinge-like joint that allows the greatest range of motion between the tibia (shin bone) and the femur (thigh bone). The bones of the stifle joint are not interlocked as are the hip shoulder and elbow joints. The tibia and the femur are held together with several strong ligaments and a fibrous joint capsule which prevent motion between the two overlying bones. There are two fibrocartilaginous meniscus that are interposed between the two bones to cushion the union between them. There are two cruciate ligaments which run between the bottom of the femur and the top of the tibia named the anterior or cranial cruciate ligament and the posterior or caudal cruciate ligament. These two ligaments provide stability or prevents motion between the two bones. The anterior cruciate is the one of these two ligaments which is more prone to damage. Once damage occurs to the anterior cruciate ligament, the two bones slide between one another with the tibia moving forward. This abnormal motion is known as an anterior drawer sign and is characteristic of cranial cruciate rupture. As a result of this rupture the medial meniscus may also be damaged as the tibia moves forward when weight is placed on the leg.

Ruptured anterior cruciate ligaments are seen more commonly in spayed or neutered animals. This increase in incidence appears to correspond with the measurement of what is known as the tibial plateau angle or TPA. The TPA is the angle measured from the tibial plateau (the top portion of the tibial crest) and an imaginary line drawn perpendicular to the long axis of the tibia. It has been found that dogs with a tibial plateau angle of greater than 35º in both limbs were 13.6 times more likely to have been neutered before they were 6 months of age. Dogs that are neutered at over 6 months of age typically have a TPA of less than 30º. It is believed that the TPA is a major factor in the amount of force the anterior cruciate ligament is subjected to. The greater the TPA, the greater the amount of stress that is places on the anterior cruciate. The greater the amount of stress on the anterior cruciate then more likely the ligament is to rupture.

Dogs neutered early are also more likely to be overweight or obese. The increase in weight also places additional stress on the anterior cruciate ligament making it more prone to rupture.

Once the anterior cruciate ruptures on one side, the ligament on the opposite side will often rupture as well. Once a tendon ruptures in one hindleg, the dog is required to place more weight on the remaining three legs especially the contralateral or opposite rear leg. In turn the additional weight places yet greater stress on the remaining rear leg and the anterior cruciate ligament. Dogs with anterior cruciate rupture are most often greater than 5 years of age.

Most pets with anterior cruciate rupture have a history of acute trauma or of suddenly turning, followed by intense pain and carrying of the affected limb. On physical examination the detection of an anterior drawer sign is diagnostic for a torn anterior cruciate. When a dog is painful and guarded it is often necessary to sedate the pet thereby gaining enough muscle relaxation to allow physical observation of the anterior drawer sign.

Surgical correction if the treatment of choice for full ligament rupture.

In cases were the anterior cruciate ligament is simply stretched, rest, weight reduction and strengthening of the quadriceps mechanism through exercise may be of benefit. Arthritis is common after injury. Damage to the anterior cruciate is the most common cause of arthritis in the stifle or knee joint of dogs.


Duerr, Felix and Colleen Duncan, “Risk factors for Excessive Tibial Plateau Angle in Large-Breed Dogs with Cranial Cruciate Ligament Disease.” JAVMA, Vol, 231, No. 11, December 1, 2007. Pp. 1688-1691.

Kustritz, Margaret, “Determining the Optimal Age for Gonedectomy of Dogs and Cats.” JAVMA, Vol 231, No. 11, December 1, 2007. Pp. 1665-1675.

Wilke, VL and DA Robinson et al. “Estimate of the Annual Economic Impact of Treatment of Cranial Cruciate Ligament Injuries. JAVMA 2005; 227: Pp. 1604-1607.

Topics: ligaments

Symptoms: limping, overweight

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