The most common knee injury in dogs is when they tear one of the two knee ligaments that stabilize the knee joint.  Called an ACL injury, it can happen when a dog is running and inadvertently steps in a hole, slips in the mud or is hit by a car, any action that puts tremendous stress on a dog’s knee. Large breed dogs which makes the knee more vulnerable, are especially prone to ACL injuries. St Bernard’s and Newfoundlands for example as well as poor physical condition in obese and elderly dogs makes them vulnerable as well. If the knee ligament is simply ripped, a period of rest may be enough to get the dog back in action but a torn ligament requires surgery to recreate the damaged tissue. Never try to diagnose this problem or administer pet medication on your own. The is a job for a vet. Remember, your pets count!