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Cause & Effect: Cruciate Ligament InjuryEverything you wanted to know (and a few things you didn't) about cruciate ligament injury in sporting dogsBy Kyle K. Kerstetter, DVM, DACVS
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The scenario is all too familiar: A client will bring his or her Lab into the veterinarian because it is limping on one of its rear legs. Examination of the dog's knee (known as a stifle joint in veterinary terms) will show telltale instability consistent with injury to the cruciate ligament.
Thus begins the client's and the dog's journey into the treatment and prognosis associated with injury to the cranial cruciate ligament in the dog. In this article, we'll explore the anatomy of a dog's knee joint, options available for correction of the instability, and what can be expected long-term in a dog with injury to the ligament.
Injury to the cranial cruciate ligament (CCL) is the most common orthopedic injury seen in dogs. A thorough understanding of the disease process should begin with the anatomy of the joint.
A canine knee joint is similar to a person's knee in many regards. The knee joint is made up by the meeting of the femur (top bone), tibia (bottom bone), and the patella (kneecap). Holding these bones together requires several structures. Primary supporting structures in the knee include the cranial and caudal cruciate ligaments (analogous to the anterior and posterior cruciate ligaments in the human knee), collateral ligaments, medial and lateral meniscal cartilages, and patella (kneecap) tendon (Figure 1).
The CCL prevents the tibia from moving in front of the femur, excessive internal rotation of the joint, and hyperextension. This makes it a very important structure in the overall stability of the joint, and it is the structure most often injured.
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The meniscal cartilages act as shock absorbers when a dog walks and can be injured secondary to CCL instability. This is especially true of the medial meniscus, the cartilage closest to the inside of the leg. This injury occurs in about 50 percent of dogs with cranial cruciate ligament injuries and is often accompanied by a "click" that can be heard when a dog walks.
One of the questions most often asked when someone learns that their dog has a cranial cruciate ligament injury is, "How did this happen?"
There are several theories to answer this question; however, the truth is that no one knows for sure. In people, there is usually significant trauma involved — football injuries being a prime example. In dogs, it is unusual that there is a single traumatic event resulting in rupture of the ligament. In most instances, there is little if any trauma involved.
The theory that I subscribe to, at this point in time, is that asymmetrical muscle contraction places abnormal stresses on the CCL, eventually weakening the ligament. As the instability progresses, small tears may occur, which may continue to progress until a full tear of the ligament takes place.
Another factor that likely plays a role involves conformation of the bones that make up the knee joint. It is important to note that whatever the underlying problem is that resulted in rupture of one CCL, the dog possesses that same underlying problem in the other knee. That's why a dog with one torn CCL has a 30 percent risk of rupturing the opposite CCL, usually within 18 months of the first injury. The common thread in this group of dogs is obesity, yet another reason to keep your dog fit and trim.
When the CCL is weakened or torn, the most significant long-term change in the joint is development of arthritis. This results in significant injury to the cartilage covering the bone ends and subsequent development of bone spurs (osteophytes). All joints with instability will develop arthritis, but the severity and the effect of the arthritis on the dog's overall comfort level vary from individual to individual.
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Most dogs with CCL injuries will show an immediate onset of lameness. This may improve over several days; however, there is usually a dramatic decline in function of the limb over time. This likely is the result of a partially torn ligament that has developed into a full tear to the meniscal cartilage. There is no benefit gained from taking a "wait and see" approach; stabilization of the joint as early as possible is what is most often recommended.
There are over 100 surgical techniques described that can be used to stabilize a dog's knee (don't worry, I won't go over all of them!). These can be divided into techniques that stabilize from inside the joint (intra-articular), and those that stabilize the knee from outside the joint (extra-articular).
The important thing to remember is that once the ligament is injured, it cannot be repaired or replaced. Even techniques that place a tendon graft along the same course are a poor substitute for the original ligament, achieving at best 30 percent of the strength of an intact CCL.
Regardless of the technique used, the surgery should entail careful inspection of the joint either by use of arthroscopy (a small camera placed into the joint) or arthrotomy (incision into the joint). This is very important to confirm the presence of a torn CCL, the degree of ligament injury, and assessment of the meniscal cartilages.
If the cartilage is injured, the damaged portion should be removed. New cartilage will form that is not quite as good as the original cartilage but will result in improved comfort for the patient.
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One of the more common intra-articular techniques utilizes a piece of the patella tendon as a graft. The tendon is split and pulled through the joint along the same line as the original ligament. Several modifications to this technique have been described, although most have similar long-term results.
A popular extra-articular method involves placement of a lateral fabella-tibia suture. This technique involves placement of a heavy suture around the fabella, a small bone located behind the femur (Figure 2).
The suture is then passed through a hole drilled into the tibia just behind the point where the patella tendon attaches. A second suture may be added around the fabella toward the inside of the leg if instability is still present. The suture is then tied very tightly to prevent forward movement of the tibia. This technique stabilizes the knee at the price of range of motion, and places abnormal stresses on the joint surface.
Comparison of the tendon stabilization and the suture technique show no advantage of one procedure over the other. Arthritis continues to progress at a rapid rate with both techniques and has been shown to be the same rate as that seen in dogs that have had CCL injury with no stabilization method.
In most instances, a stable joint is more comfortable than an unstable joint, which explains why improvement is often seen after either procedure even in the face of arthritis. Both techniques also often result in continued instability of the joint, which may contribute to the rapid progression of arthritis.
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It is also worth noting that approximately 10 percent of dogs that had a normal medial meniscus at the time of the initial surgery will develop injury to the medial meniscus, requiring a second surgery.
One of the best treatments for dogs with CCL injuries, especially large active dogs like our Labs, is the tibial plateau leveling osteotomy (TPLO). To understand how this techniques stabilizes a dog's knee, let's look back at the anatomy.
The top of the tibia is called the tibial plateau. The tibial plateau of a human is relatively flat because we walk upright; the tibial plateau of a dog is sloped toward the back of a dog's leg because a dog walks on all fours (Figure 3). As long as the CCL is intact, it acts as a restraining band that holds the femur on top of the sloped tibial plateau.
When the CCL is injured, this restraining band is lost, and you essentially have the rounded joint surface of the femur resting on a hill.
When the dog places weight on the limb there is compression at the joint, resulting in the femur sliding down the hill. The TPLO removes the hill by cutting the bone and rotating the top of the tibia in such a way that the majority of the hill is removed. This allows other supporting structures of the knee to stabilize the joint. The result is a dynamic form of stabilization that spares range of motion.
The first step in doing a TPLO is determination of the degree of slope seen in the tibial plateau by taking very specific X-rays. The dog is taken to surgery and the bone cut with a special saw.
The bone is then rotated a specific number of millimeters determined from the X-rays taken prior to surgery. A bone plate is applied to allow the bone to heal in its new position.
Advantages of the TPLO are that it offers an earlier return to function, better overall function, and development of less arthritis than anything else I have done in a dog's knee.
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A study comparing the TPLO to the suture technique showed a 200 percent increase in the amount
of arthritis that developed in knees of dogs having the suture technique done, as compared to a 50 percent increase in dogs that had the TPLO done.
The TPLO is unique in that it is a patented procedure, which means a surgeon must take a course and be licensed to perform the procedure, which limits its availability; however, more people are being added to the list every day.
The reason this procedure was patented is to ensure it is done correctly. It is a technically challenging surgical method that is best employed by an experienced surgeon. I personally believe the procedure is so superior to other methods that I will not even offer other treatments to dogs that require athleticism to perform their everyday function. This group includes hunting dogs, field trial dogs, show dogs, agility dogs, and dogs involved in law enforcement, to name just a few.
After surgery, it is important to do physical rehabilitation on the knee. Exercises that improve passive and active range of motion are very important. Swimming may be the best exercise and, fortunately, most Labs are more than happy to take to the water. All activity must be under the guidance of your veterinarian to prevent injury from pushing the limits too far too fast. Long-term use of a product containing glucosamine may also help with overall joint health.
With appropriate attention, a CCL injury does not mean the end of an active life for your Lab. Proper care as well as a good rehabilitation program can ensure a long, happy, active life for dogs suffering from this injury.
Dr. Kerstetter is a board certified small animal surgeon at Michigan Veterinary Specialists in Southfield, Michigan.
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copyrighted ©1990-2006, by Mark Joseph Walsh.