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Orthopedic Surgery > Cranial Cruciate Ligament Insufficiency
What is a CCL and what does it do?
Although the knee (or stifle as it is referred to in dogs) 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 weight bearing surfaces, 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 and weight bearing creates a force that pushes the femur down the slope of the tibia. This force is called “tibial thrust” and it is the job of the CCL to prevent this motion. Each time the dog bears weight, the CCL is called to work. If you think of the tibial plateau as a hill and the femur as a car parked on the hill, the CCL is the brake. If the ligament ruptures, it allows the femur to slide down the slope or, in our example, the brake releases and the car rolls down the hill. When the ligament is ruptured, each time the dog bears weight this motion occurs and causes discomfort. Within the joint, there will be inflammation and swelling, referred to as synovitis and effusion. The menisci are the “shock absorbers” of the knee and are located between the bottom of the femur and top of the tibia. There is a meniscus located on the inside (medial) and outside (lateral) aspects of the knee. When the knee is unstable due to a CCL rupture, either complete or partial, these structures are at risk for injury.
How does a rupture of the CCL occur?
Rupture of the CCL can occur in several different ways. There may be a single incident which causes a sudden complete rupture of the ligament. When this occurs the dog is typically painful and non-weight bearing. The rupture can also occur over time. Dogs with a high tibial plateau angle (greater slope) have greater stress to the CCL and the ligament can tear incrementally. Dogs can also partially tear the ligament due to an incident. With a partial rupture, the dog typically experiences an intermittent lameness. The majority of partial ruptures will progress to a complete rupture within weeks to months. Common causes of partial and/or complete ruptures include hyperextension and internal rotation of the knee from sudden turns, stepping into a hole; jumping – if the force of the cranial tibial thrust exceeds the breaking strength of the CCL; repetitive normal activities; and degeneration with aging. Obesity can increase the risk of a rupture as can the “weekend warrior” routine, in which the pet is relatively inactive during the week but very active on weekends. Dogs that have ruptured the CCL in one knee have a 50% to 70% greater chance of rupturing the CCL in the 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 that my pet has a rupture of the CCL?
If the CCL rupture is complete and acute, often the pet will be non-weight bearing lame. With rest, the lameness may improve but will return as the pet is more active. However, in the case of a partial or gradual rupture, the pet will be weight-bearing lame 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 pet sits with the affected leg out to the side. He or she may 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 limb. Dogs that have ruptured the CCL in both knees do not routinely carry or off-load a particular limb since he or she does not have a good limb to stand on.
How is a rupture of the CCL diagnosed?
Diagnosis of a rupture of the CCL first requires an orthopedic examination. The examination typically begins with a visual analysis. Lameness during a walk and off-loading of the limb when standing is commonly observed. The lameness may be mild to non-weight bearing. When sitting, the patient will often demonstrate a positive “sit test” in which the affected limb is out to the side rather than tucked against the body. The musculature of the hind limbs will be assessed. Muscle atrophy of the affected hind limb is common. Often, especially in a more chronic case, thickening of the affected knee, called medial buttress, is noted. The patellar tendon, which runs along the front of the knee, is assessed. The edges of the patellar tendon are easily palpable in a healthy knee, but effusion within the joint, common to CCL injuries, will make palpation of the patellar tendon less distinct. Joint stability can be assessed through manual manipulation. The “cranial drawer” test involves holding the femur with one hand and the tibia with the other, testing for forward motion of the tibia in relation to the femur, called cranial drawer or cranial thrust. This forward tibial drawer or thrust is tested throughout range of motion of the knee. Motion elicited in flexion only typically indicates a partial rupture of the CCL. Motion elicited throughout range of motion typically indicates a complete rupture. A nervous patient with good quadriceps muscle tone can make this test challenging. Cranial thrust can also be evaluated by applying tibial compression. This technique involves placing the index finger of one hand over the patella (knee cap) with the tip resting on the tibial crest and flexing of the hock (ankle) with the other hand. An intact CCL will prevent forward motion of the tibia during hock flexion, therefore, if tibial thrust is elicited, it is likely the CCL is compromised. Radiographs of the stifle can be useful to evaluate the presence of effusion (excessive fluid within the joint) and arthritis. If these assessments are not completely diagnostic, arthroscopic evaluation of the joint and structures may be recommended. If arthroscopic evaluation reveals the ligament is injured, surgical correction can be performed at that time.
What are the surgical options for a ruptured CCL?
There are four surgical options for correction of this injury. Extracapsular Stabilization or Lateral Suture Stabilization, the TightRope CCL procedure, the Tibial Plateau Leveling Osteotomy (TPLO), and the Tibial Tuberosity Advancement (TTA).
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