Back Leg Limping in Dogs Think Knee First
I generally examine at least one limping dog per day, two thirds of which are limping on one of their back legs…what we term rear limb lameness. I find it curious that dog owners seem in most cases, all but convinced that the source of the problem is coming from the hip. I am not sure why this is, perhaps all the press that genetically deformed hips (a condition known as hip dysplasia) has gotten in the past several years, perhaps it is the result of internet speculation, but whatever the reason, the pet owner more often than not finds out by the end of the examination that the hip is not the primary source of the lameness.
It is not to say that a dog with rear limb lameness necessarily has good hips. In fact, many dogs have very poor conformation in their hips, a testament to our ongoing insistence in continuing to purchase puppies from pet stores and back yard breeders that do not know a thing, nor have a care, about responsible, ethical breeding. But while poor hips are not conducive to an optimal quality of life – to be sure bad hips will lead to degenerative joint disease and chronic pain eventually the most common source of canine rear limb lameness that is severe and acute enough for owners to bring the dog to the vet, is the knees.
In toy breed and small breed dogs, the most common source of pain emanating from the knees is medially luxating patella, a condition where the knee cap continually pops out of place in the direction toward the center, or medial, region of the body. This occurs due to a genetically inherited angular deformity of the rear limb that leads to a chronic pull of the knee cap in the medial direction. Like deformed hips, it too is the result of unethical/irresponsible breeding practices (Those pet stores and back yard breeders are just lovely, aren’t they?). Medially luxating patellas are in most cases very amenable to surgical repair (again, more on this below), but add in the aforementioned additional injuries, and your dog now has what we term the deranged knee, where there are now multiple injuries/abnormalities within the knee joint that require surgical attention.
Well the knee caps are not just where they are for decoration, but they serve a very important purpose. The patellar tendon is a very large tendon that is the convergence of the quadriceps muscles which are capable of placing a lot of force across the knee joint. The knee cap – or patella – beneath it, serves to ease and redistribute the forces exerted across the joint. When it is out of place, not only is it directly painful, but it leaves the knee susceptible to injury, such as tears of the CCL ligament and/or meniscus (more on these below).
For medium and large breed dogs, medially luxating patella occurs occasionally, but it is really not all that common in these guys. Medium and large breed dogs with rear limb lameness most commonly have knee pain from a tear of the CCL ligament and possibly the meniscus as well.
The CCL ligament (cranial cruciate ligament) serves the same function as the ACL (anterior cruciate ligament) in people, which is the major stabilizing ligament of the knee joint. Likewise, the meniscus in the dog’s knee serves the same purpose as the meniscus does in people, which is to act as padding between the articulating surfaces of the long bones (the femur and tibia) that comprise the knee joint. Tears of the CCL ligament lead to instability and pain of the knee joint, while tears of the meniscus are additional sources of pain and inflammation within the canine knee. The injury occurs for one or a combination of these 3 reasons:
1.) Many large breed dogs as the result of unethical and irresponsible breeding inherit steep angles of the head of the tibia (the chin bone) that put excessive force on the CCL ligament (Aren’t those pet stores and back yard breeders becoming ever more lovable?) 2.) Obesity is a major contributing factor to many of these injuries, as the increased weight of obese dogs puts additional stress across major stabilizing ligaments like the CCL. 3.) Back luck…sometimes an athletic dog simply plants to change direction just the right way and the ligament just goes, as commonly happens in human athletes.
(I will address treatment for these injuries, as well as medially luxating patella just below I ll get there, I promise)
So why did I feel compelled to take the time to write this post? Well, I have seen a rash of these injuries as of late and all too commonly things are far worse than they should be. The pet owner is advised by some un-medically-trained know it all on some pet forum or otherwise determined through their own “internet research” – that the problem lies in the hip and the best thing he or she can do is put the dog on an over the counter glucosamine product, rather than pay his/her vet to tell him/her what he/she already knows. Only, in the process of the little dog gimping around on a medially luxating patella for a month or longer, the CCL may also rupture, so now we have gone from medially luxating patella surgery to a deranged knee surgery; which translates to more invasiveness for the patient, longer recovery period, and more expense to the owner.
In the case of the CCL tear case, the longer the dog gimps around on the injured knee, the higher the likelihood of concurrently tearing the meniscus, a common injury that occurs with CCL tears. With larger dogs relying on the other limb for support, they also may weaken that knee and predispose it to CCL injury later on, giving the dog and the owner two CCL tears do deal with rather than just one. The grossly unstable knee also leads to other degenerative changes over time, such as the growth of bone spurs, damage to the cartilaginous surfaces of the joint, and thickening of the joint capsule, further complicating our ability to surgically repair the injuries.
As far as diagnosing and treating canine knee injuries, if your “internet research” has brought you here, your research this time around has served you well. Surgical repair and rehabilitation of the canine knee is one of my special interests, for which I have done extensive postdoctoral training in advanced surgical repair of the knee and post-operative rehabilitation. Rather than rewrite all of the information I have for you in this post, please refer to the following articles I wrote on medially luxating patella and cranial cruciate ligament ruptures, respectively:
So the next time your dog shows significant lameness of a rear limb for more than a couple of days, I advise you not to be so quick avoid the vet and just throw glucosamine at the problem as far too many other pet owners do. A proper examination and early diagnosis of a knee problem will not only save you expense in the end, but save your dog a lot of unnecessary suffering. And in the event, the problem is the hip? There are much better things we can do than just throw glucosamine at it…but that is for another day, on another post.
Dr. Roger Welton is the President of Maybeck Animal Hospital and CEO/Chief Editor of the veterinary information and blog online community, Web-DVM.