The stifle joint (in layman’s terms called the knee) of the dog is similar to a human’s knee. The cranial cruciate ligament is located inside the joint and is responsible for maintaining a stable joint. One of the important functions of the ligament is to prevent forward and backward sliding of the femur on the tibia bone (drawer motion). Our veterinarian specializes
Cranial cruciate ligament rupture is the most common orthopedic condition that we treat.
This problem afflicts all ages and breeds of dogs. Frequently cruciate ligament rupture is a gradual process and not simply due to a single traumatic injury. Most dogs have a predisposing factor such as age-related ligament degeneration, pre-existing inflammation, anatomical abnormalities, and excessive slope of the top of the tibia bone, which cause the ligament to rupture. Clinical signs of early cruciate disease includes: stiffness or very mild lameness. As the disease advances and the ligament progressively tears, the lameness becomes more pronounced. Complete tears initially result in nonweight-bearing on the limb, but as time goes on the dog will start to use the limb. It is unusual the lameness will resolve in a large breed dog with no surgery. Rupture of the cruciate ligament in both knees is common. In fact, one out of three dogs will also develop a cruciate rupture of the opposite stifle. Below is a photo of a front view of the stifle joint in a dog illustrating the cranial cruciate ligament (labeled c) and the front horn of the medial meniscus (labeled M), which is a cartilage pad located within the stifle joint that is commonly damaged with cruciate ligament tears.
WAGON MODEL USED TO EXPLAIN INSTABILITY OF THE KNEE JOINT
The tibial plateau of a dog’s stifle is sloped. Understanding the importance of the tibial slope when the cranial cruciate ligament is torn is somewhat difficult. We therefore present a model of a wagon on a hill, which is tied to a fence post. The slope of the hill represents the tibial plateau, the wagon represents the femur bone, and the cable represents the cranial cruciate ligament. If the cable is torn, the wagon will roll down the hill (see fig below). Likewise, when cranial cruciate ligament is torn the femur bone will slide down the slope of the tibial plateau. When surface that the wagon is placed on is level and weight is put in the wagon, it does not to roll backward (see fig below). In the dog, the tibial plateau leveling osteotomy levels the slope of the tibial plateau so that the femur no longer slides down the plateau. Thus a dynamically stable joint is created even when no cruciate ligament is present.
Below are radiographs showing the side view of a stifle before and after surgery. Take note that the slope of the tibia prior to surgery is 26.5 degrees and the final slope is 5
degrees. Prior to surgery, the femur bone slides down the slope with weight-bearing, but cannot slide backward after the slope has been leveled with surgery.
When the cruciate ligament is ruptured, the slope of the tibial plateau, along with the forces exerted by the calf and quadriceps muscles cause the femur bone to slide down the top of the tibia bone called the tibial plateau. This in essence causes the tibial plateau to thrust forward with each weight-bearing stride and is called cranial tibial thrust.
This thrusting results in excessive wear of the cartilage of the joint. In addition, as the tibia thrusts forward it stretches the tissues which surround the joint, which causes pain.
Excessive cranial tibial thrust also can tear of one of the cartilage pads in the knee called the medial meniscus. This usually results in a meniscal bucket handle tear or crush injury. The tibial plateau leveling osteotomy or TPLO can eliminate cranial tibial thrust, thus creating a dynamically stable stifle and sound gait.
We do TPLO using Synthes locking plate. For further information you can visit www.tploanswers.com.