Cruciate Ligament Injury in Dogs

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

Has your dog suddenly started limping on one of his back legs? There are many different reasons for limping in dogs, and knee injuries are among them. One of the most common knee problems seen in dogs is a cruciate ligament injury. Of course, your vet is the only one who can determine the actual cause of your dog's limping. If your vet thinks the cruciate is the problem, here's where you can learn all about cruciate injuries in dogs.

What is the Cruciate Ligament?

The cruciate ligament is a major part of the canine knee. Cruciate injuries are among 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 problem, 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 perhaps 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 more prone to this type if injury, as they carry more weight and often have weakened joints. Additionally, some dog breeds/types are predisposed to cruciate ligament injuries.

While a cruciate rupture cannot always be prevented, keeping your dog at a healthy weight and providing plenty of exercise (but 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.

Although rest and medication may help, the most recommended method of treatment for cruciate ligament injury is surgical repair. In general, prognosis after surgery is good. However, there are different surgical approaches, each with its pros and cons. If your dog has a cruciate injury, you may wish to talk to your vet about getting a referral to a board certified veterinary surgeon. There, you can discuss the best surgical options.  The following types of surgical procedures are available to repair torn cruciate ligaments in dogs:

Cruciate Surgery: Extracapsular Repair

The traditional surgical procedure is often called the extracapsular repair. In this method, the damaged ligament is removed and a very strong suture essentially replaces the function of the cruciate ligament. The tissue of the knee heals over several months and the suture eventually breaks, leaving the healed tissue to stabilize the knee. This is a relatively quick and uncomplicated procedure that can be successful for many dogs, especially smaller dogs. It is also less expensive than other methods. However long-term success is not excellent. Many dogs will re-injure the knee. That is why this procedure is less commonly recommended by veterinary surgeons.

Cruciate Surgery: TPLO

An increasingly popular surgical option is called the tibial plateau leveling osteotomy (TPLO). This is a significantly more complex procedure than the traditional extracapsular method and must be performed by a specially trained veterinarian, specifically a board certified surgeon. The TPLO alters the mechanism of the knee joint, allowing it to function properly without a cruciate ligament. A cut is made into the top of the tibia (tibial plateau). Then, the tibial plateau is rotated to change the angle and a metal plate is affixed keep the bone in place.

Over several months, the bone heals into its new position. Partial improvement can be seen within days. However, full recovery will take several months, so cage rest is essential. Generally, the long-term prognosis is very good, and re-injury is uncommon. The plate does not need to be removed unless problems occur later. As with any surgery, complications are possible. The TPLO is significantly more expensive than the traditional surgery.

Cruciate Surgery: TTA

A third surgical method is called the tibial tuberosity advancement (TTA). Like the TPLO, the TTA allows the knee to function without a cruciate ligament. The details of this method are slightly different, but the TTA still involves cutting of the tibia and placement of hardware. Some surgeons describe the TTA as a less invasive procedure than the TPLO - and with a faster recovery. However, other surgeons see little difference. The dog's anatomy is also a deciding factor. The cost of the TTA is comparable to the TPLO.

Cruciate Surgery Recovery in Dogs

Regardless of the surgery type, a post-operative resting period of eight weeks or more is crucial to the healing process. In addition, physical therapy is often recommended and can be extremely successful for long term recovery. Compliance with your vet's recommendations will give your dog the best chance of full recovery with fewer complications. As with any orthopedic surgery, know that it is not uncommon for dogs to develop arthritis in the future. However, with care and compliance, your dog can live a full, healthy, and comfortable life.