Several ligaments make up the knee. Their function is to maintain joint stability. Among these, the cranial cruciate ligament is responsible for limiting the internal rotation of the tibia, the cranial movement of the tibia as well as the hyper extension of the knee. With dogs and more rarely with cats, the cranial cruciate ligament can rupture. This rupture may be degenerative or traumatic in origin. It should be noted, of course, that a degenerated ligament is much more susceptible to traumas than a perfectly healthy ligament. In dogs, a degenerative component is often responsible for RCCL. Age, as well as a bad conformation of the knee, are the two factors able to precipitate a degeneration of the ligament. In cats, obesity seems to be the predominant factor.
Often, in dogs, both knees are affected within a 1-2 year interval. The RCCL may be partial or complete. Actually, the cranial cruciate ligament is composed of a craniomedial band as well as a caudolateral band. The tearing of just one of these bands is considered a partial rupture. Generally, a partial rupture will progress towards a complete one. With the RCCL, the knee becomes unstable because the ligament can no longer carry out its function. This instability stimulates the development of osteoarthritis can be the source of significant pain.
With the orthopedic examination, a localized pain in the knee may be demonstrated. With a complete rupture, a drawer movement (tibia moves cranially compared to its normal position) is present when the knee is positioned in flexion as well as extension. With a partial rupture, depending upon which band is affected, the drawer movement may be absent or even, be present only when the knee is in flexion if the craniomedial band is affected. A sedative is sometimes necessary to succeed in detecting the movement, particularly in large breed dogs with a strong muscle mass. Furthermore, with an acute RCCL, joint effusion at the level of the patella may be felt. With chronic RCCL, a muscular atrophy of the affected paw may be observed and cracking might be felt during flexions/extensions of the knee. This cracking is often associated with meniscal lesions combined with the RCCL. The x-ray may also be a tool in helping with the diagnosis. However, the ligaments are not visible on x-rays and so we rely on the changes to the global conformation of the knee. When the condition is acute, the radiographs may be used to eliminate other differential diagnosis (ex: joint fracture, tumoral process, etc.) whereas when the condition is chronic, radiographic changes may be present (compression of the triangle of fat on the cranial side of the joint, joint effusion as well as the formation of osteophytes at the level of the patellar fossa of the femur, the tibial plateau and/or the distal aspect of the patella).
Nonetheless, these radiographic changes are not specific to RCCL because other conditions affecting the knee may cause them (ex: infection, neoplasia of the soft tissues, osteoarthritis, etc.) Magnetic resonance is a very precise method for the final diagnosis of RCCL and allows, at the same time, for the evaluation of the meniscus that may have been damaged secondary to this condition.
The rupture of the cranial cruciate ligament can be treated medically or surgically. As a general rule, surgery is more strongly recommended than medical treatment, particularly for large breed dogs. For small breed dogs and cats, a medical treatment may be acceptable when there are budgetary constraints.
This treatment is only recommended for small patients under 10kg who have a rather sedentary lifestyle. Normally, an improvement can be seen in 3 to 6 weeks, apart from patients with concurrent damage to the meniscus. However, the amplitude of movement of the knee will remain forsaken for the rest of the life of the animal. This is why this method is discouraged for active dogs. The treatment consists of 6 weeks of complete rest with anti-inflammatory medication. These medications may have significant side-effects when used long term. A damaged knee is more susceptible for developing osteoarthritis than a healthy one; therefore anti-inflammatories may unfortunately become necessary for the long term for adequate pain control. Tears in the ligament of the other knee occur in 40% of cases, typically, in the following 12-18 months. When radiographic changes are present, the incidence passes to 40% to 60%.
Several methods of knee reconstruction are available. The choice depends on the surgeons’ preferences, the weight of the animal, the lifestyle of the patient as well as the budget of the owners. It has been shown that 85 – 90% of dogs demonstrate a post-surgical improvement satisfactory for the owners. The 2 main techniques use at our hospital are the Flo and the TPLO.
Flo technique (extracapsular reconstruction technique, therefor at the exterior of the joint capsule):
A hole is created on the crest of the tibia. A non-absorbable, nylon suture string, adapted to the weight of the dog, is passed through this hole. The string is then passed through the deep fascia and around the fabella to then be tightened. The drawer movement is eliminated. Evidently, the string finishes by rupturing with time. The goal of the surgery is to stabilize the joint just long enough for healing to take place. Therefore, this technique is recommended for small patients because the implant risks giving way prematurely in heavier patients. Generally, osteoarthritis will establish itself more quickly in knee than if it was repaired through other surgical techniques: the TPLO for example.
TPLO (Tibial Plateau Leveling Osteotomy):
To be able to employ this technique, good quality radiographic views are required beforehand in order to evaluate the conformation of the knee. In fact, the slope of the tibia should be measured to evaluate the correction to be made so that it becomes almost non-existent. The TPLO technique consists of reconstructing the anatomy of the knee to avoid the drawer movement of the tibia. The caudal part of the tibial head is therefore sawed, then deviated with a rotation and fixed into place using a plaque and a screw. In this manner, the angle of tibial plateau from which the femur is apposed is diminished and the tibia no longer has a tendency to shift cranially. The joint is stabilized and the development of osteoarthritis slowed down greatly.
A bandage is put in place for the first 24-48 hours. Once the bandage is removed, a physical rehabilitation program can be established. Specific exercises will be used to stimulate the gain of muscle mass, all while permitting a return to the functioning of the member as quickly as possible. Strict rest is necessary just until a follow up x-ray shows adequate healing. The healing time varies from one dog to another, taking from 4 to 12 weeks. A progressive return to exercise should be made, starting with short walks on a leash only. If rest is not respected, the implants may give way prematurely before the bone has completely healed.