The most common cause of rear limb lameness in the dog is rupture of the cranial cruciate ligament. This injury leads to degenerative changes in the knee joint including cartilage damage, arthritis and meniscus injury. Tibial plateau leveling osteotomy (TPLO) surgery stabilizes the joint and proves effective in returning the knee back to full function.
A normal dog's knee joint works like a hinge, keeping the animal's leg stable as it bends. The cranial cruciate ligament prevents forward movement of the tibia, internal rotation and hyperextension of the knee. When the cranial cruciate ligament ruptures, the "hinge" becomes loose and no longer functions effectively. The loose knee joint is no longer stable and as a result, the dog suffers pain, inflammation, and eventually develops degenerative arthritis.
Cranial cruciate rupture in humans differs from that in dogs. In humans, it occurs as a sudden injury due to a skiing, football or other sports-related accident. In dogs, the ligament rupture can occur in several different ways. Like humans, the ligament can rupture suddenly, causing complete rupture with severe pain and non-weight bearing lameness. More often though, the ligament is partially torn, resulting in low-level lameness that may improve initially over time. As time goes on; however, the partial ruptures cause pain and mild lameness. With continued trauma to the affected knee, the joint becomes inflamed, arthritic and gets worse.
When the cranial cruciate ligament tears, the femur has the tendency to slide down the slope on the top of the tibia (tibial plateau). This sliding results in a great degree of instability within the joint, leading to the development of arthritic changes and pain. The TPLO surgery levels this slope and eliminates the need to replace the ruptured cruciate ligament. The surgery changes the anatomy of the knee joint by rotating the top of the tibia (plateau) and plating it into place. This procedure requires that a bone cut be made in the tibia, which is then stabilized with a specialized bone plate.
Only veterinarians who have been trained in this technique are competent to perform TPLO surgery.