The diagnosis of a ruptured cranial cruciate ligament usually can be made upon physical examination. Two tests, the positive cranial drawer test, and the positive tibial compression test, will confirm the diagnosis. The positive cranial drawer test, in which the dog's knee is bent slightly and pressure is applied to the bones comprising it, is performed to check for instability within the joint. A positive tibial compression test also assesses the stability of the knee joint; this test may be more sensitive in detecting looseness in heavily muscled dogs. It may be necessary to sedate large dogs before performing the test. When the injury is chronic, the cranial drawer and tibial compression tests may be less effective assessments because their results will be more difficult to evaluate, since the body will have built up scar tissue in the joint capsule in an attempt to limit the abnormal motion.
If the dog's meniscal cartilage -- the knee's "shock absorbers" -- has been torn, the veterinarian may feel a "meniscal click." Thirty to 50 percent of dogs that have knee joints with chronically ruptured cruciate ligaments will experience damage to their cartilage, resulting in arthritis. X-rays can help confirm the diagnosis and give an indication of how much arthritis already is present. This information may be important for determining prognosis. X-rays can also rule out diseases such as rheumatoid arthritis and fractures that may display similar symptoms.
Occasionally, the veterinarian will obtain and analyze a sample of joint fluid in an attempt to rule out other types of arthritic diseases. However, this procedure usually will not be performed unless there is suspicion that an underlying disease is causing the ruptured cruciate ligament.
