Clean Run Magazine - July 2007 - 55

Anatomy Four ligaments passively stabilize the canine stifle joint: the cranial cruciate, caudal cruciate, medial collateral, and lateral collateral ligaments as shown in Figure 1. The cranial cruciate ligament is functionally composed of a craniomedial band and a caudolateral band. While the craniomedial band remains taut throughout a full range of motion (flexion and extension of the knee) the caudolateral band becomes lax during flexion. The medial and lateral menisci are semilunar fibrocartilage structures positioned between the articular surfaces of the femur and tibia. The menisci have several important functions, including energy absorption and stress transfer across the stifle joint, joint stabilization, prevention of synovial membrane (joint capsule) impingement between the femur and tibia, and joint proprioception. complete rupture within months. Common causes of partial and/or complete ruptures include hyperextension and internal rotation of the knee from sudden turns or stepping into a hole; jumping if the force of cranial tibial thrust exceeds the breaking strength of the CCL; repetitive normal activities; and degeneration associated with aging. Obesity can increase the risk of a rupture, as can the “weekend warrior” routine, when the dog is relatively inactive during the week but very active on weekends. Dogs that have ruptured their CCL in one knee have a 50% to 70% chance of rupturing the CCL in their other knee. Therefore, surgical correction is recommended as soon as possible to decrease the stress placed on the uninjured CCL, thereby decreasing the risk of CCL rupture to that knee. What are signs of a CCL rupture? The presenting history of dogs with CCL pathology is varied. The onset varies from peracute after a traumatic or athletic injury to slow and insidious. Dogs with an acute onset of non-weightbearing lameness often improve over several weeks as the inflammation subsides, particularly with rest and nonsteroidal anti-inflammatory drugs (NSAIDs). This initial improvement, however, does not indicate a resolution of the condition. Commonly, dogs with early or minor CCL pathology will initially return to near-normal function with time, rest, and NSAIDs only to present several weeks or months later with a more severe and persistent lameness. In many cases, this history indicates progression to a complete CCL rupture or the development of a secondary meniscal injury. Femur What is a cranial cruciate ligament and what does it do? Although the knee joint in dogs is similar to ours, the forces applied to the joint during weight bearing are vastly different. Our hip, knee, and ankle joints are perpendicular to our weightbearing surface: our feet. When we stand, there is minimal stress to the ligaments in our knee. Dogs, however, stand on their toes with the ankle elevated and the knee forward. The top of the dog’s tibia (tibial plateau) is sloped. Weight bearing creates a force that pushes the femur down the slope of the tibia. This force is called “tibial thrust” and the job of the CCL is to Patella prevent this motion. Each time the dog bears weight, the CCL is called into work. If you think of the tibial Lateral plateau as a hill and the femur as a collateral ligament car parked on the hill, the CCL is the brake. If the ligament ruptures, it allows the femur to slide down Cranial cruciate the slope or in our car example, the ligament brake releases and the car rolls down the hill. When the ligament is ruptured, each time the dog bears Lateral weight this sliding motion occurs meniscus and causes discomfort. Within the joint, there will be inflammation and swelling, referred to as synovitis and effusion. Caudal cruciate ligament Medial meniscus Medial collateral ligament How does a CCL rupture occur? Rupture of the CCL can occur in several different ways. There may be a single incident that causes a sudden complete rupture of the ligament; the dog typically show signs of pain and non-weightbearing. A rupture can also occur slowly over time. In addition, dogs can also partially tear the ligament. With a partial rupture, the dog typically experiences an intermittent lameness. The majority of partial ruptures will progress to a July 07 | Clean Run Fibula Tibia Figure 1: Anatomy of the canine stifle (knee) PHOTOS COURTESY OF SHERMAN CANAPP © Cindy Telley If the CCL rupture is complete and acute, often the dog will be nonweightbearing on the affected leg as seen in Figure 2. In the case of a partial or gradual rupture, however, the dog will be weight bearing or have an intermittent lameness. Lameness will often worsen with activity. Stiffness upon rising and/or a stiff gait is another common complaint. You may note that your dog sits with the affected leg out to the side as shown in Figure 3. The dog may also have difficulty rising and be less active. Physically, you may note a swelling or thickening of the knee and muscle atrophy (wasting) in the affected leg. Dogs that have ruptured the CCL in both knees do not routinely carry or off-load their weight to a particular limb since they do not have a good leg to stand on. Gait Analysis Gait evaluation is used to detect lameness and confirm the limbs involved. In some instances, it can strongly direct the orthopedic specialist toward a specific joint as the source of lameness. Closely observing dogs standing still, walking, 55 Figure 2: Non-weightbearing lameness Figure 3: A classic posture, the dog is sitting with the affected limb out to the side

Clean Run Magazine - July 2007

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