Cruciate Ligament Injury in Dogs

Dog After Knee Surgery
Dog After Knee Surgery. Photo: Chris Stein/Getty Images

The cruciate ligament is a major part of the canine knee. The cruciate injury is one of the most common orthopedic complications seen in dogs. Sometimes called ACL or CCL tear, a ruptured cruciate is often a painful and immobilizing injury. While not a serious or life-threatening injury, it is still one that must be addressed for the sake of your dog. As a dog owner, it is relatively likely you will eventually see this injury occur in one of your dogs.

It is important to understand the signs and treatments of this injury, as well as know how to prevent it.

Brief Anatomy of the Canine Knee

The knee, or stifle, is a complex joint comprised of the patella (kneecap), cartilage called the menisci, and a series of ligaments connecting the femur (thighbone) to the tibia (shin bone). Together, these components enable the joint to function properly. The knee has two essential stabilizing ligaments that cross over one another inside the knee joint. They are called the cranial (or anterior) cruciate and the caudal (or posterior) cruciate. Malfunction of even one part of the knee can cause a great degree of discomfort and lameness. Of the many knee injuries that can occur, a cruciate injury is the most common.

Causes of Cruciate Ligament Injury

A cruciate ligament injury can occur in dogs for several reasons. In some cases, it is simply the result of an athletic injury in a healthy dog.

This could even mean landing "wrong" when running or jumping. Overweight or obese dogs are definitely more prone to this type if injury, as they carry more weight and often have weakened joints. Additionally, some dog breeds are predisposed to cruciate ligament injuries.

While cruciate rupture cannot always be prevented, keeping your dog at a healthy weight and providing plenty of exercises (not too strenuous) can minimize the risk.

When the Cruciate Ligament Goes Bad

A cruciate ligament injury is the result of a partial or complete rupture (tear). The cranial (anterior) cruciate ligament is the one more commonly affected, though the caudal (posterior) can rupture as well. When the cruciate ligament tears, the tibia moves freely from under the femur, resulting in pain and abnormal gait. Sudden lameness in a rear leg is often the first sign of injury. If an injury remains unaddressed, arthritic changes can begin quite quickly, causing long-term lameness and discomfort. If your dog shows signs of pain or lameness, it is best to have your vet do an exam within a couple of days.

Diagnosing Cruciate Ligament Rupture

Your vet will perform an orthopedic examination, trying to isolate the pain to a specific area and ruling out injury to the foot, hock, or hip. If a knee injury is suspected, your vet will check for a cranial drawer sign - this involves manipulating the femur and tibia to feel for instability. A positive drawer sign occurs when the tibia can be moved forward independent of the femur, mimicking the motion of opening a drawer. Stifle radiographs (x-rays) may also be performed to check for arthritis or fractures.

In a few cases, a referral for more advanced diagnostics may be recommended, such as arthroscopy or MRI.

Conservative Management of Cruciate Ligament Rupture

While most dogs with cruciate injuries require surgery, a small number will improve with conservative therapy. This mostly involves several weeks of cage rest, with very brief, calm leash walks for bathroom breaks only. Some vets will place knee braces or prescribe anti-inflammatory medication, but these methods are most often ineffective. A small percentage of dogs will eventually recover with cage rest, but typically these are dogs that weight less than 25 or 30 pounds. Even the dogs that do recover can re-injure the knee in the future, or even tear the cruciate ligament on the other knee.