Understanding knee injuries requires a basic understanding of the anatomy of the joint. The stifle, or knee, is the joint in between the femur and the tibia. Between the two bones lies a cushion called the meniscus, which is composed of two C-shaped pieces of cartilage. The stifle joint is stabilized by a series of ligaments: the cranial and caudal cruciate ligaments, the medial and lateral collateral ligaments, and the patellar ligaments. The cranial and caudal cruciate ligaments cross over the front of the stifle joint, and are responsible for keeping the tibia from sliding too far forward, or too far backward, respectively. The medial and lateral collateral ligaments lie on either side of the knee, with the lateral being on the outer aspect of the joint, and the medial on the inner aspect. These two ligaments function to stabilize the sides of the joint, and keep the bones from sliding away from each other in a medial or lateral direction when the stifle is extended. The patellar ligaments are those that hold the patella, or kneecap, in place and allow for its movement when extending and flexing the knee. (diagram of stifle anatomy, specifically cruciates)
The caudal cruciate ligament keeps the tibia from sliding too far caudally (backward) when the knee is flexed. It works in concert with the cranial cruciate to provide rotational stability to the joint. The caudal cruciate ligament is analogous to the posterior cruciate ligament (PCL) in humans. Injury to this ligament can result in partial or complete tears, and the subsequent instability caused progressive degenerative joint disease (DJD), or arthritis in the stifle joint.
improves, but not to the extent it was prior to the injury. The animal may have a normal gait when walking, but since the ligament’s main function is to stabilize the joint when flexed, lameness is most apparent during strenuous activity.
Isolated tears of the caudal cruciate ligament are usually caused by a blow to the tibia in a cranial-to- caudal direction. In other words, from an impact that hits the top of the tibia from the front and forces it backwards. This occurs most commonly in car accidents or from falling onto the leg when the knee is flexed. Because it takes a lot of force to damage this ligament, it is common to have concurrent damage to other ligaments in the knee. This emphasizes the importance of accurate diagnosis as to the extent of damage to the stifle.
Medical management of a caudal cruciate ligament rupture is an option, but only in small dogs or cats that lead inactive lives, and consists of restricted activity (leash walks only) for 8 weeks. In larger and more active dogs, surgical repair is recommended. Surgery involves removing the remnants of the torn ligament, and stabilizing the joint using one of several techniques. In one method, special sutures are placed outside the joint capsule (extracapsular) on either side of the knee at the patellar tendon and are secured to the tibia on the medial side and to the fibula on the lateral side. (show diagram/rads of repair). Another option is to redirect the placement of the medial collateral ligament and placing it more caudally using a screw, in order to stabilize the joint. A third surgical approach is called tenodesis of the popliteal tendon. The tendon of the popliteal muscle wraps around the back of the joint, and can be used to stabilize the knee by placing a screw to secure the tendon to the bone.
Because rupture of the caudal cruciate ligament is a result of acute trauma to the joint, there is no specific way to prevent the injury.
Following surgical repair, prognosis is good to excellent for return to normal function in most animals. Proper post-surgical care and physical therapy can help ensure a successful outcome. Fortunately, DJD does not appear to progress as rapidly after caudal cruciate ligament injury as it does after injury to the cranial cruciate ligament.