Ron Hines DVM PhD 6/24/06

The Problem:
Your dog’s knee is also called its stifle. The two most common problems that I see that involve this joint are a dislocating knee cap and torn or stretched cruciate ligaments. The stifle is the joint that bridges the upper and lower leg bones, the femur and tibia (see diagram). To add stability to this joint, Nature has provided some very strong ligaments. Two of these ligaments are attached in a crosswise fashion, hence the names, anterior and posterior cruciates or “cross” ligaments. These ligaments act together with two outer bands of fibrous ligament, the lateral collateral ligaments, and the kneecap in maintaining joint stability.

Cruciate ligament damage is most commonly seen in overweight middle-aged dogs. When I think of this problem, I picture a chubby. neutered female or male Labrador retriever leading a sedentary and pampered life. Another group of dogs that suffer from this disease are those receiving corticosteroid medications. The problem appears suddenly – often after some sudden twisting movement or jumping up or out of an elevated location. The pet often yelps at the sudden pain that occurs. In light to moderate weight breeds (less than 25 pounds), use of the knee often becomes normal with time and rest. So I place lightweight dogs on anti-inflammatory and pain management medications as well as glucosamine and plan a program of rest and physical therapy while the joint heals.

Diagnosis:
Examination of a painful stifle is best done under anesthesia or heavy sedation. Besides being painful, the muscles of this joint are often in spasm making diagnosis difficult or impossible in unanaesthetized pets. After I relax the pet, I place one hand on the thigh to immobilize the femur and with my other hand I attempt to move the tibia anteriorly and posteriorly (see diagram). A normal joint will not move in these directions because intact cruciate ligaments prevent it. Only in knees where the cruciate ligament(s) have snapped is this forward and backwards motion possible. We call this motion the “drawer” effect. In old injuries to the knee, scarring may prevent some of this motion but not the pain. In old injuries, the lateral collateral ligaments that stabilize the knee are stretched and loose as well. In most cases it is the anterior cruciate ligament that is ruptured. When there is any question in my mind, I compare the looseness of the affected joint with the normal one. Particularly when the tear is old, the affected knee pops and clicks when it is manipulated and on occasion these joints are puffy with excess fluid. X-rays will not detect the damaged ligaments but they will pick up later arthritis as it develops. In the rare instances where both legs are affected the diagnosis can be missed as it may appear to be a spinal nerve injury although it is not.

Treatment:
Even in large breeds, lameness due to this injury decreases with time. However, if this injury is not treated surgically in the larger breeds, instability of the knee will lead to arthritis of the joint and eventual inability to use the affected leg. There are many different surgical techniques to repair an unstable knee. They are best done soon after the injury occurs. Some of these techniques actually replace the torn cruciate ligament and require opening the knee. These are called intracapsular techniques. Other methods do not enter the knee but instead attempt to add strength to other structures that surround the knee to compensate for the torn ligament. These are called extracapsular techniques. I use a combination of both. I separate out in the knee area a strip of the fibrous tissue that surrounds the joint called the fascia lata. With the distant end still attached to the leg I thread the cord I have fashioned through a needle and pull it through the joint along the rout that the torn ligament took and then through a hole or tunnel that I bore through the femur. I then sew the new “ligament” in place. After I have closed the knee I sew out any slack I find in the joint capsule and strengthen the joint by sewing two small bones called fabella to the tibia with a suture that remains intact for the rest of the pet’s life. When I am finished I bandage the knee in elastic gauze for three weeks to restrain motion and limit exercise to short walks on a leash for an additional month.

Long Term Results:
Surprisingly, all surgical methods generally have good results. When widely differing procedures all result in improvement with time it is wise to question whether time itself may be the curative element. None-the-less, it is considered good practice in veterinary medicine in the United States to treat all these cases in larger breeds surgically. Quite a few of these dogs will rupture the cruciate ligament of the remaining good leg within three years. Weigh reduction helps keep the affected knee stable. So does avoiding future extreme activities for your pet.

An article in the January 15th 2005 issue of the Journal of the AVMA does not give an overly optimistic evaluation of surgery for cruciate ligament damage. This paper found that only 14.9% of dogs treated with lateral suture stabilization (LSS), 15% of dogs treated with intracapsular over-the-top stabilization (ICS) and 10.9% of the dogs treated with tibial plateau leveling osteotomy (TPLO) regained normal leg function subsequent to surgery. Improvement was seen in only 15% of dogs treated with ICS, 34% of those treated with TPLO and 40% treated with LSS. Remember older dogs do just fine on three legs when the use of one rear leg is reduced.

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