- What is it?
- Who gets it?
- What are the signs?
- How is it diagnosed?
- Why did this happen to my dog?
- How is it treated?
- Can it be prevented?
- What is the prognosis for my dog?
What Is It?
Understanding knee injuries require 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.
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.
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Who Gets It?
The caudal cruciate ligament is slightly larger than its cranial counterpart, and injury to this ligament is relatively uncommon. This is due to the biomechanics of the stifle: the caudal cruciate is positioned in such a way that physical forces that cause ligament injury are directed toward the cranial cruciate ligament. It is also less common simply because the types of injuries that cause rupture of the caudal cruciate are uncommon. That being said, these injuries do occur, in dogs or cats of any age, breed, or gender may be affected. They tend to more frequently occur in large breed dogs.
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What Are The Signs?
Dogs with rupture to the caudal cruciate ligament will have non-weight bearing lameness that gradually improves, but not to the extent it was before 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.
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How Is It Diagnosed?
Your veterinarian can diagnose damage to the caudal cruciate ligament by evaluating the stifle for signs of instability. Diagnosing tears of the caudal cruciate ligament is more difficult than diagnosing ruptures of the cranial cruciate ligament because unless the damage is severe and includes multiple ligament injuries, laxity in the joint is often less obvious. Radiographs may help diagnose this condition. Small bone opacities may be associated with tearing of the ligament may be present on the x-rays, and in certain views of the stifle, the tibial plateau may be displaced. Arthroscopy can also be used and is the only way to get a definitive diagnosis.
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Why Did This Happen To My Dog?
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 backward. 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.
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How Is It Treated?
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 the fibula on the lateral side. Another option is to redirect the placement of the medial collateral ligament and place it more caudally using a screw, 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.
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Can It Be Prevented?
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.
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What Is The Prognosis For My Dog?
Following surgical repair, the 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.
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