Clean Run - October 2010 - 69

Canine Cruciate Disease
Part 1
By Peter J. Lotsikas, DVM, Diplomate ACVS, Lisa M. Fair, CMT, CCRT (Candidate), Faith M. Lotsikas, DVM, CCRT

A Review of

Cranial cruciate ligament (CCL) deficiency is the most common cause of hind limb lameness in the canine and is estimated to affect one million dogs annually. The canine CCL is analogous to the anterior cruciate ligament (ACL) in humans; however, there are significant differences in the biomechanics of the human knee and canine stifle (knee) and the way in which deficiencies occur between the two species. In humans, the primary cause of an ACL injury is an acute, traumatic, typically sports-related event. Although CCL injury in dogs can occur in a similar manner, it is more often the result of a progressive degenerative process termed cranial cruciate disease. This etiological distinction must be considered when discussing the management of the condition. Despite the high prevalence and the long-standing history of this condition, we still do not fully understand its etiology. Furthermore, although several treatment options exist, no one method has been found to be the superior treatment for all cases. While the subject matter is vast, we hope to clarify the current understanding of this condition. Anatomy
The stifle joint is stabilized by both passive constraints (ligaments, menisci, joint capsule) and active constraints (muscles and tendons). The CCL is the primary passive stabilizer of the stifle joint. It is composed of two bands, the craniomedial band that is taut in all phases of flexion and extension of the knee, and the caudolateral band that is taut in extension, but lax in flexion. Together, these bands limit internal rotation, hyperextension, and cranial tibial translation (forward motion of the tibia in relation to the femur). A major difference between dogs and humans is the way in which forces are transmitted through the limbs during weight bearing. When a human is standing, minimal force is placed on the anterior cruciate ligament. However, because dogs stand on their toes with a flexed stifle, their
October 10 | Clean Run

cruciate ligament is continuously under load. Another anatomical difference is the angle of the top of the tibia, called the tibial plateau angle or slope. In humans, this slope is relatively flat. In dogs, this slope can vary between 14°-60°. When the canine knee is weight bearing, the tibia is displaced forward as the femur slides down the slope of the tibia, much like a car without brakes slides down a hill. The steeper the angle, the more significant the force. This is called tibial shear force. In a healthy stifle, the CCL opposes this motion. The integrity of the CCL is most easily assessed by the extent of cranial tibial translation present in the stifle joint. This movement can be elicited on physical exam of a CCL-deficient limb with manual manipulation,

Clean Run - October 2010

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