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Dog Cruciate Ligament Injury: Pathophysiology

One of the most common orthopedic diseases that veterinarians see is canine cruciate ligament injury. This disease affects all breeds, genders, and ages of dogs. The disease is so prevalent in dogs that a study was performed to assess the estimated economic impact of treating cruciate ligament disease in dogs for the year of 2003 and found the cost to pet owners to be $1.32 billion (JAVMA, 2005). The unfortunate part is that costs for treatment have only risen since 2003.

The cranial cruciate ligament in the dog is similar to the corresponding anterior cruciate ligament in a person and perform a similar function in both. The cruciate ligaments are called this because they form a cross or”X” within the knee. The ligaments are named by where they originate on the tibia. Thus, the cranial or anterior cruciate ligament originates on the front of the tibia and inserts on the back of the femur. The function of the cranial or anterior cruciate ligament is to prevent cranial or foward sliding of the tibia compared to the femur as well as to prevent hyperextension and excessive internal rotation of the knee.

In people, damaging the cruciate ligament requires some form of trauma to the knee such as getting hit in the knee like a football player, or falling and twisting the knee abnormally like skiers. Dogs can tear their cranial cruciate ligament in a similar way but can also injure it from normal, everyday activities like walking and running, without significant trauma. There are theories that the slant or angle of the top surface of the tibia where it comes in contact with the femur is to blame for this type of degenerative injury in the dog. Instead of all of a sudden coming up lame on the leg after running and falling, these dogs present with a slowly progressive lameness that can occur over months to a few years. Unfortunately, because degeneration of the ligament over time is usually the cause, it is very common that both knees have the same problem and often dogs tear the cranial cruciate ligament in the second knee within 1-2 years.

The first sign that is seen with cruciate ligament tears is lameness. This lameness can be all of a sudden while playing or some other vigorous activity or it can be a slowly progressive lameness which worsens over time. Often, when the lameness is slowly progressive, the dog will show exacerbation of the lameness with exercise or after a prolonged rest.

The diagnosis of a cranial cruciate ligament injury can be made by your veterinarian palpating your dog’s knee. There are two tests that can be done to feel for abnormal sliding of the femur and tibia called the cranial drawer test and the cranial tibial thrust test. If abnormal movement is felt, then you can be comfortable saying that the cranial cruciate ligament is torn. In cases where the ligament is not completely torn, movement may be subtle and then further testing such as radiographs to show abnormal swelling or arthritis can be performed to help make the diagnosis.

Making the definitive diagnosis of a cruciate ligament tear is done by visually inspecting the ligament during surgery. This can be done by opening the joint to look at the ligament (arthrotomy) or by using a camera on the end of a scope (arthroscopy) to see within the joint. Many factors such as size of the dog, age of the dog, activity level of the dog, financial limitations of the owner, and surgeon’s preference are all factors that determine what the best course of treatment is for each dog.

Robert Vonau is a board certified veterinary surgeon practicing in Denver, CO. Repairing dog cruciate ligament injuries is what he spends most days doing. Find out more about dog cruciate ligament injury at my site www.petsurgerytopics.com

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