Limping dogs are almost a daily occurrence at the Animal Hospital at Thorndale. The knee (stifle) joint of the dog is one of the weakest joints in the body. Just as athletes (football players, in particular) frequently suffer knee injuries, dogs also have knee injuries. The knee joint is relatively unstable because there is no interlocking of bones in the joint. Instead, the two main bones, the femur and tibia, are joined with several ligaments. When severe twisting or excessive extension of the joint occurs, the most common injury is a rupture of the anterior cruciate ligament (ACL) or sometimes called the cranial cruciate ligament (CCL). When it is torn, instability occurs that allows the bones to move in an abnormal fashion in relation to one another. When this happens, it is not possible to bear weight on the leg without pain and instability. In an ACL tear, the lower leg can slide forward beneath the upper leg bone. Other structures in the knee joint, most notably the menisci, may also be damaged. The menisci are two cup-like cartilage structures on the top of the tibia, upon which the condyles or “rollers” at the end of the femur rest. When a meniscus is damaged, a chip of cartilage, called a “joint mouse” floats free into the joint space and can be very painful as pressure is exerted on the knee joint by standing or walking.
Contributing Factors
Planting a foot and rapidly twisting on the knee leads to the tear of the ACL. Dogs running on uneven ground, landing badly on their legs while catching flying balls or Frisbees, and sudden changes of direction, especially when being “body slammed” by a playmate can all potentially lead to a tear.
Newer studies in Golden Retrievers, show that in this particular breed, early spay or neuter may increase the likelihood of a ACL tear later in life. This predisposition has not been verified in other breeds being studied, but certainly warrants further study. It is important to note that spay and neuter have numerous health benefits and certainly most dogs do not tear their ACLs.
A special note is appropriate concerning the dog’s weight. Obesity or excessive weight can be a strong contributing factor in cruciate rupture. The ligament may become weakened due to carrying too much weight; this causes it to tear easily. Obesity will make the recovery time much longer, and it will make the other knee very susceptible to cruciate rupture. If your dog has a weight problem, there are prescription diets that can be used to assist weight reduction.
Prevalence
Rupture of the ACL is most common in middle aged and older dogs, particularly those that are overweight house pets.
Causes
In younger dogs, rupture of the ACL is usually the result of trauma to the stifle joint. In some cases, the ligament may only partially tear; however, this will eventually lead to complete tearing of the ligament. When ACL rupture occurs in older dogs, it is most frequently initiated by a progressive degenerative change in the ligament with eventual total rupture.
Clinical Signs
Dogs with a ruptured ACL are usually lame and may refuse to bear weight on the affected leg. Many of these dogs will hold the leg in an elevated position with the knee bent and the toes pointed downward. The gliding forward of the lower leg relatively to the upper leg, is not usually visible to an owner and requires an examination by a veterinarian. Eventually, most dogs become more willing to bear weight but some degree of lameness remains. It is important to remember that dogs cannot verbalize their pain but not using a leg is a clear sign of pain and needs to be addressed.
Diagnosis
The most reliable means of diagnosing this injury is for the examining veterinarian to move the femur and tibia in a certain way to demonstrate the instability. This movement is called a “drawer sign.” It can usually be demonstrated with the dog awake. If the dog is very painful, has very strong leg muscles, or is uncooperative, it may be necessary to use sedation in order to examine the joint adequately. Radiographs of the knee are also important to evaluate the joint for inflammatory changes, possible joint mice or other common stifle problems. Older large breed dogs are candidates for certain boney cancers at the knee joint so ruling out or early detection of this problem requires x-rays. Similarly, many larger dogs will have hip problems (dysplasia, severe osteoarthritis) which may complicate treatment options.
Treatment
Correction of ACL rupture requires surgery. If surgery is not performed within a few days to weeks, arthritic changes will begin that cannot be reversed, even with surgery. Occasionally, the injury that causes a ruptured anterior cruciate ligament will also result in tearing of one or both of the menisci or cartilage cups on the tibia At the time of surgery, these are examined and removed if necessary. There are several surgical procedures being used to correct an ACL tear. The weight, health and size of the dog, and the existence of meniscal tears will determine the best option for your dog.
TPLO for Cruciate Ligament Repair
One of the most common surgical approaches to repair an ACL tear for larger breed dogs is called a TPLO (Tibial Plateau Leveling Procedure). We recommend that this procedure be performed by a surgical specialist for the best results. This procedure involves reshaping the knee joint so that the upper leg bone (femur) rides on a more horizontally leveled surface (the top of the tibia). Anatomically, ACL tears are thought in part to be due to the downward tilting of the top of the tibia so the femur can readily slide off the back edge, tearing the ligament in the process. In a TPLO procedure, the top back portion of the tibia is actually cut off from the rest of the bone, and then re-anchored with screws and plates so the surface upon which the femur rides is more level to the ground. In the hands of experienced orthopedic surgeons, this gives the best repair. Many of these dogs can return to full activity. Post operative care and rehabilitation involved after a TPLO are the same as for a broken leg. Most dogs are clearly more comfortable and using the leg when they come home from the hospital, but their activity must be restricted for 8-16 weeks, depending on how the bone is healing. Owners must plan on leash walking and confining their dogs as directed during the healing process. Physical therapy is also beneficial for these dogs. Follow up radiographs will be needed during recovery to ascertain that the bone is healing properly.
Other Techniques and non-surgical options
A number of other surgical procedures may benefit smaller dogs. Surgeries may involve creating a false ligament through the joint or stabilizing the joint with very strong sutures placed outside the joint. With careful selection of the patient, these procedures can also give a successful repair.
In some cases surgery is not an option. Owners need to be aware that arthritis in the knee will likely develop in these dogs. The dog’s body will eventually try to stabilize the joint by reacting to the additional stress placed on the ligaments surrounding the knee. These ligaments will thicken over time and reduce the instability in the knee. In very small dogs (and cats), allowing the body to “scar in” or thicken these ligaments may be a reasonable option. Pain relieving medications will be needed to help make your pet more comfortable during the healing process. Joint supplements may be beneficial.
Prognosis
Following proper and prompt surgical correction, the joint is sound again. Most dogs walk and run without any lameness; however, some have either a mild limp or lameness associated with cold and damp weather.
Occasionally, a dog that has a ruptured cruciate ligament will become sound (will no longer limp), even if surgery is not performed. However, progressive, degenerative arthritis will develop and result in lameness a few months later. Once these degenerative changes are established, the lameness cannot be corrected, even with surgery.