ACL injury in the dog

Part 1 Do dogs have an ACL (anterior cruciate ligament?) in their knee?

This is the first blog in a series addressing the most common orthopedic injury in dogs.  The answer to the question is yes, dogs do have ACLs, and yes, just like human athletes, dogs can tear their ACL.  Because dogs walk on 4 legs we call the ACL the CrCL or cranial cruciate ligament.  This ligament is found inside the knee (also called the stifle).  Essentially, it has the same purposes in dogs as it does in humans:  1) prevent the tibia (lower leg bone) from sliding forward past the femur (upper leg bone); 2) prevent the tibia from rotating internally (toward the inside) about the end of the femur; 3) stop the knee from hyperextending.

When the ACL or CrCL is injured it may be fully torn or partially torn.  This can happen all at once (traumatic injury) or it can tear gradually over months or years resulting in intermittent episodes of mild to moderate lameness that improves and then comes back.  The latter is more common in dogs and it is thought that CrCL injury in dogs is more commonly part of a degenerative disease of the CrCL rather than a result of trauma.  There is a great deal of research devoted to understanding this very complex issue.  Whether the ligament is completely torn or partially torn the dog can be mildly to severely lame and may not bear any weight on the leg.

Sometimes the damaged CrCL is not the only problem.  Inside the knee there are 2 cushions called the menisci.  Sometimes the meniscus that is positioned on the inside or medial aspect of the knee is torn in the process of injuring the CrCL.  When this happens the dog is especially lame and subject to pain.  Typically surgery is performed to remove the injured part of the meniscus.

Lastly, it is not uncommon for a dog to damage both CrCLs.  This can occur all at once or more commonly, one is injured and the second within 2 years.  The reason for this is still not clear, but seems to be related to the notion of the degenerative process mentioned above and to the conformation (in-born structure) of the individual dog.  My own dog, Griffin, injured her left CrCL and within 1 year the right.