Dear Dr. Thompson: We have a 3-year-old very active German Shepherd/Belgian Malinois mix (about 80 pounds) who has been limping periodically, especially after strenuous exercise. Besides her twice-a-day walks, she also goes for bike rides, plays Frisbee with us, and just loves to run and jump. While at the vet for something else, we asked about her limp and were told that she had arthritis in her left rear knee probably due to some previous injury and that the knee cap was in place. He also said to let them know if it became more painful and he would prescribe pain killers. We didn't think to ask at the time but want to know if there's anything we could do to help prevent further damage or pain? Or are there things we should not do because they may make our dog's condition worse?
The previous injury your veterinarian was describing was most likely damage to one of the major ligaments inside the knee called the cranial cruciate, or in people the ACL. This ligament stabilizes the knee from front to back and large breed dogs are very susceptible to this injury. Some dogs will suddenly tear the ligament during running or an athletic event. However, the more common scenario is a series of small microscopic tears in the ligament which result in a gradual progression of instability and pain in the knee. The limping you describe after strenuous activity is probably more microscopic damage to the ligament.
X-rays of the knee will help in diagnosing the problem. Often with partial tears of the ligament it is difficult to feel any instability or what is called a "drawer" movement since it mimics a drawer sliding forward. Large dogs may even need sedation to fully evaluate the instability since their strength can counteract your veterinarian's attempts to manipulate the knee. While the ligament itself can't be seen on an X-ray, the arthritic changes in and around the knee joint, coupled with swelling inside of the knee are all hallmarks of a cruciate injury. Your veterinarian mentioned the knee cap was in place and that is important because a dislocated knee cap can accompany this injury or mimic the symptoms.
For most dogs this problem requires surgical intervention to stabilize the knee. Without treatment this will progress to a full tear or the arthritic changes will progress and a significant loss of function will result. These factors will also raise the likelihood of tearing the cruciate in the other knee due to the added strain.
Dogs are very different than people in that you and I can get around without an ACL - it may interfere with our ability to do many things, but dog's anatomy is significantly different. The cruciate ligament is a critical stabilizer for walking, let alone more athletic pursuits. There are a couple of surgical options for repairing the knee that your veterinarian can explain to you. Some surgeries, called geometry modifying procedures are especially helpful with partial tears since they take the strain off of the ligament and some studies have gone back and found these partially torn ligaments will go on to heal.
Questions for Dr. Gary Thompson can be e-mailed to firstname.lastname@example.org or mailed to The Blade, Attn. Ask the Vet, 541 North Superior St., Toledo, OH 43660. Dr. Thompson regrets that he cannot answer individual letters.