When dog owners observe chronic hind leg lameness, the common assumption they make is that it is probably because of a hip issue. This is likely because of the notoriety of hip dysplasia, an inherited malformation of the hips that can lead to chronic hind limb lameness and degenerative joint disease. Its not to say that hip dysplasia is not a legitimate possible source of hind leg lameness in dogs, it is just far more common for injury or disease of the knee to be the source of pain that is causing the chronic limping specifically in a hind limb.
So why is the knee so much more likely to cause lameness in the limbs of dogs versus the hips or other joints of the hind limb? There are two reasons. First, disease of or injury to the knee is more common than diseases of or injury to other joints of the hind limb. Second, when a dog knee is not healthy, it is more painful than disease in other joints because of the dog’s conformation.
Dogs actually stand on their toes with their heels in the air, a stance we would call standing “tip-toed.” In addition to standing tip-toed, their knees are partially bent at a 45 degree angle, thereby always engaging their knee joints, not just when they are walking and running, but also when they are merely standing. If you would like you know how this feels, stand on your tip-toes and bend your knees 45 degrees, then try walking if you are able.
While this is a great conformation for explosive speed with the aide of their front limbs, it is not a good recipe when there is pathology within the knee joint cause pain and instability. The most common source of knee pain in large breed dogs is tear of the cranial cruciate ligament, or CCL, the major stabilizing ligament of the canine knee (the equivalent of the ACL in humans). For small breed dogs, the most common source of knee pain is from a chronic dislocation of the patella (knee cap) called medially luxating patella. Medially luxating patella occurs from an inherited angular limb deformity that we commonly call being bow-legged. The outward bowing of the knee joint predisposes the patella to dislocate medially (toward the center of the body).
That stated, we do occasionally see CCL tears in small breed dogs and medially luxating patella in large breed dogs, but generally speaking, CCL tears tend to be more prevalent in big dogs, and medially luxating patella more prevalent in small dogs. This article is the first of a series of three articles, with the next two detailing the surgical procedures I recommend to repair these CCL tear and medially luxating patella in dogs, so…stand by.
Related: The benefits of Modified Maquet Procedure (MMP) over TPLO in dogs
Dr. Roger Welton has two decades of canine knee surgery experience and two post doctoral certifications in reconstructive surgery of the canine knee