Cranial cruciate rupture is by far the most common orthopedic condition in dogs and there is a great deal of information to be found, but as with many things in life, not all the information out there is accurate. There are also a few interesting aspects biomechanically, genetically, and microscopically with the condition that differ from the injury in people.
A short anatomy lesson is needed to help sort out the alphabet soup that makes up the major ligaments of the knee.
A ligament connects a bone to a bone and a tendon attaches a muscle to a bone. There are four major ligaments in the knee and one large patellar tendon. The medial and lateral collateral (MCL, LCL) ligaments are the sides of the knee joint and provide lateral stability to the joint. The cranial and caudal cruciate ligaments (anterior and posterior in people) cross inside of the knee joint and are the major front to back stabilizers.
Caudal cruciate (CaCL or PCL) injuries are very rare in dogs, leaving the cranial cruciate ligament (CrCL or ACL) as the primary source of instability in the knee arising from damage to the ligament. Limping on one or both hindlimbs is the classic symptom in dogs and often people report a history of limping that waxes and wanes with time. Diagnosis is generally made via feeling the knee for instability and S-rays. However, not all dogs with ACL tears will have the classic instability and many larger dogs will resist the manipulation since it can be painful.
While many of the dogs I see may have an event where the owners feel caused the actual tear, rarely is it a single event in dogs. ACL rupture in dogs generally has a progressive nature and this is manifested by recurring bouts of stiffness or limping which improves with rest.
Biomechanically the dog knee is considerably different than the human knee, and the ACL is a much more critical stabilizer for dogs during movement and when standing. Essentially every weight bearing event for a dog’s back leg requires a fully functional ACL and if any injury to the ligament is sustained, no matter how minor, the ligament continues to be used and abused which leads to further deterioration of the ligament with time.
This is further complicated since there is a degenerative component to ACL disease in dogs as well. This means that at a microscopic level inside the ligament there are biochemical changes that lead to further deterioration with time. This is important when considering early partial tears since these will progress with time. The analogy I use when explaining the progression of the condition is that once a dog sustains any damage to its ACL you have started rolling a ball downhill. This ball will roll downhill at different speeds with each case being different but the ultimate outcome being chronic instability and pain in the affected knee and surgery will be needed to stabilize the knee.
Your veterinarian will help you understand what surgical options are available depending on your dog’s breed, size, and anatomy.
Questions for Dr. Gary Thompson can be emailed to firstname.lastname@example.org or mailed to The Blade, Attn. Ask the Vet, 541 N. Superior St. Toledo, OH, 43660. Dr. Thompson regrets that he cannot answer individual letters.
Guidelines: Please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Comments that violate these standards, or our privacy statement or visitor's agreement, are subject to being removed and commenters are subject to being banned. To post comments, you must be a registered user on toledoblade.com. To find out more, please visit the FAQ.