According to James K. Roush, D.V.M., MS and Diplomate of the American College of Veterinary Surgeons, “cranial cruciate ligament (CCL) rupture is the most common cause of hindlimb lameness in dogs.”
Untreated cranial cruciate ligament injury quickly results in osteoarthritis of the knee joint. Arthritic changes can be identified on radiographs as early as six weeks after ligament rupture. The condition sometimes occurs bilaterally. With both rear limbs hurting, the patient puts the most weight on the one that hurts the least.
WHAT CAUSES CRANIAL CRUCIATE LIGAMENT RUPTURE?
Dr. Roush says it’s a “chicken-or-egg-first quandary.” Recent studies in the Newfoundland breed, a very large dog, suggests that the tendency can be inherited. Because 30% of large breed dogs present with bilateral ligament rupture, there is a strong suggestion that both ligaments may have been genetically inferior. Bilateral disease does not occur as frequently in small breeds as large. Most large breed dogs have radiographic (X-ray) evidence of arthritis prior to ligament rupture. Therefore, an as-yet-unidentified process is believed to have caused these dogs to suffer a gradual degeneration of the ligament, leading to its rupture. A much smaller percentage of large breed dogs experience CCL rupture acutely, usually from strenuous exertion and/or hyperextension of the knee joint, placing excessive strain on the ligament.
Tears can be complete or partial. Even partial tears cause significant pain, and, thus, limping. The American College of Veterinary Surgeons advises that most partial tears proceed to become complete.October 16, 2013
Small-breed dogs, however, have their own set of predisposing factors. Longstanding patellar luxation damages the CCL over a long period of time.
Cranial cruciate ligament rupture is rare in young dogs, except in cases of trauma, especially when the victim is hit by an automobile. Even then, their young bones usually break instead of rupturing the ligament.
OTHER RISK FACTORS FOR CRANIAL CRUCIATE LIGAMENT RUPTURE
- Neutering (some studies, none of which are universally accepted, show at least a statistical relationship between neutering and CCL rupture)
- Excessively straight hindlimb conformation
- Immune-mediated diseases of the joints
- Increased tibial plateau angle (not all studies support this finding)
- Excessive patellar ligament-plateau angle
WHAT ABOUT THE OTHER LEG?
In large breed dogs, expect the other CCL to “go.” In one study Dr. Roush quotes, 48% of Labrador retrievers ruptured the contralateral CCL within a median time of 5½ months.
While much research is ongoing in the area of CCL rupture, studies have yielded little information on how to prevent the condition.
Next week: Surgical options. See you then, Dr. Randolph.