The most common orthopedic problem in a dog is tearing of the anterior cruciate ligament in the knee. This ligament stabilizes the joint and prevents a forward motion of the tibia when the dog is weight bearing.
In the past there were many surgical procedures used to recreate the ligament. Many involved placing strips of tissue through the knee and anchoring it to the femur. These procedures have since fallen out of favor. The TPLO is considered to be the most advanced surgical procedure for repairing a torn anterior cruciate ligament.
The TPLO (Tibial Plateau Leveling Osteotomy) involves redirecting the forces in the knee to prevent the forward motion. This is accomplished by making a circular cut on the top of the tibia and rotating the fragment around to flatten the slope of the bone. A special bone plate is implanted to stabilize the bones as they heal. The procedure was developed byDr. Barclay Slocum of Slocum Enterprises in the mid 1990’s.
Your dog usually begins using the leg within a few days following the surgery. Recovery time is usually 12 to 16 weeks. As the bone heals, there is a gradual return to the use of the leg after confinement and some physical therapy.
Facts and Description of TPLO Surgery
Tibial Plateau Leveling Osteotomy (TPLO-Slocum Technique)
The most common cause of rear limb lameness in the dog is rupture of the cranial (anterior) cruciate ligament. This leads to painful degenerative changes (osteoarthritis) in the stifle (knee) joint including cartilage damage, osteophyte (bone spur) production, and meniscal injury. This technique, developed by Dr. Barclay Slocum, has given dogs the ability to achieve the highest levels of performance and function.
Although the knee joints of both dogs and humans are similarly constructed, the forces within are very different. This is due to differences in anatomy. In humans, the hip, knee, and ankle joints are parallel to each other and perpendicular to the weight bearing surface (the feet). Humans can stand easily with little stress on any ligamentous structure.
Dogs, however, stand on their toes with their heel in an elevated plane. (see Fig.1). The upper portion of the canine tibia (the tibial plateau) is sloped downhill toward the rear of the knee joint. Weight bearing creates a force that pulls the femur down the sloping tibial plateau, thereby shifting the tibia (shin bone) out from underneath the dog. This force is called cranial tibial thrust. It is opposed only by the cranial cruciate ligament (see Fig.2).
Just as an unrestrained wagon on a hill would tend to roll down the hill, the cranial cruciate ligament acts like the cable in Figure 3A to restrict the downhill roll of the femur. With every step a dog takes, stress is applied to the cranial cruciate ligament. Over time, dogs with a high tibial plateau slope place enormous stress on the anterior cruciate ligament. Therefore, when the cranial tibial thrust is too great, the cranial cruciate ligament ruptures (see Fig.4).
The cranial cruciate ligament rupture can occur in several different ways. There may be a single incident which causes a sudden complete rupture of the ligament with severe pain and non-weight bearing lameness. Cranial cruciate ligament ruptures can also occur in small increments or a little bit at a time, a literal tug-of-war with inside the knee joint. These are known as partial ruptures of the anterior cruciate ligament. These partial ruptures cause a small amount of pain and a mild lameness. When partial ruptures proceed to complete ruptures, the transition is often gradual, a veritable “rollercoaster” of pain and lameness.
Two other important structures in the knee are the medial and lateral menisci (cartilage pads) (see Fig.1). These shock absorbers are increasingly prone to injury when the stifle joint is unstable from a cruciate ligament tear. Approximately 50% of human and canine patients have “torn cartilage” within the knee at the time of surgical repair.
The TPLO procedure is used mostly for large, active dogs due to the stability it provides under extreme repetitive stress. Traditional surgical techniques require prolonged confinement to allow healing of the synthetic or natural cranial cruciate ligament replacements. These surgical repairs may fail due to the difficulty in confining large, active dogs for prolonged recovery periods. Any activity may lead to stretching of any synthetic repair.
Once the cranial cruciate ligament ruptures, the tibia can slide forward and the femur is free to ride down the slope of the tibial plateau, just as the wagon rolls down the hill once the cable is cut (see Fig. 3A). The meniscus is often damaged as the femur rides over the top of it. When the ligament tears, pain, swelling, and marked lameness will occur. If not stabilized, the joint will become dramatically arthritic over time. Rest and anti-inflammatory medications have little effect upon the pain and lameness the dog experiences.
Diagnosis is made upon eliciting forward motion of the tibia (cranial drawer sign), named after the front to back motion of a dresser drawer. This is easy in acute, complete ruptures but may be more subtle in chronic or partial tears. Mild sedation to allow muscle relaxation and radiographs (x-rays) to demonstrate arthritic changes and swelling may be necessary to obtain a diagnosis.
The tibial plateau leveling osteotomy is used to neutralize the effect of cranial tibial thrust (see Fig. 5). The procedure levels the tibial plateau, thereby eliminating the need for the cranial cruciate ligament as a restraint against cranial tibial thrust (see Fig. 3B). In other words, rather than replacing the cable which broke in the first place, this procedure will level the surface and eliminate the need for the cable. Meniscal injuries are also addressed during the surgery.
Healing takes about two months for the bone and slightly longer for the soft tissues. Strict confinement is mandatory during the healing process. Because the plateau leveling allows the joint pain to rapidly subside, the major problem during recovery is excessive patient activity prior to the completion of bone healing. Unrestricted or under-restricted activity will result in the failure of the surgery. Most patients return to controlled activity in 6-8 weeks and near full levels of activity in three to four months. Patients can usually return to athletic competition (field trial, hunting, agility trials) by six months post-operatively.
Greater than 90% of dogs enjoy a seemingly pain-free and limp-free quality of life. It is important to understand that the knee cannot be returned to a 100% return to function. In addition 30-40% dogs that rupture one knee, will have the opposite knee rupture, often times within the next 12-18 months.