Pet owners sometimes ask what would happen if we didn’t address a torn anterior cruciate ligament (ACL). Some colleagues suggest conservative treatment as a perfectly valid option. A nonsurgeon colleague even wrote elsewhere that since people often don’t need surgery for an ACL tear, then we shouldn’t need it in dogs. Respectfully, this shows a basic misunderstanding of the differences in functional anatomy between dogs and humans. Let’s mention two: Humans are straight legged. Dogs always have their knees flexed when standing. The human tibial plateau angle is somewhere around 7 degrees. Dogs’ tibial plateau angles vary from around 20 to over 60 degrees, with a back-of-the-envelope average of 24 to 28 degrees in most of my tibial plateau leveling osteotomy (TPLO) patients. How many reasonable, objective, ethical, honest reasons can you find to recommend conservative treatment as opposed to surgery? 1. Pain Patients with an acutely torn ACL are typically in pain. When the tear becomes chronic, pain might subside to some degree, but it stills hurts. One of the reasons patients are limping is because they are in pain. (It also is because of stifle instability.) Holding the affected leg up or limping hurts less than full weight-bearing. 2. Degenerative joint disease We routinely notice during surgery that patients with long-standing ACL tears have more degenerative joint disease (DJD) than patients with an acute injury. This, in turn, leads to pain. Patients with partial tears typically have less DJD than patients with complete tears. Acute tears also regularly lead to less DJD than chronic tears. Therefore, the sooner we perform the surgery, the better for the patient. 3. Fibrosis Fibrosis is what we rely on when we recommend conservative treatment for an ACL tear. Experience proves that fibrosis alone is not enough to provide good function, at least in medium- and large-breed dogs. Scar tissue is manifested by the medial buttress, which is thickening of the medial joint capsule (and not the medial collateral ligament, as often is believed). The medial buttress is a pathognomonic sign of an ACL tear. In turn, fibrosis leads to our next point. 4. Decreased range of motion A long-term consequence of DJD and fibrosis is a decreased range of motion of the stifle. Patients with chronic ACL disease commonly experience a decreased range of motion. This might not matter much to a couch potato, but it will affect the performance of an active family pet or a working dog. Figure 2: Severe DJD in a stifle in a 7-year-old Labrador retriever with chronic ACL disease. 5. Muscle atrophy Patients who favor a hind leg classically show various degrees of muscle atrophy because of disuse of the leg. This can be assessed easily by measuring the thigh girth with a simple tape measure or a leash. You also can measure the width of the thighs on a good, symmetrical ventrodorsal radiograph that includes the pelvis and knees. 6. Exercise intolerance Obviously, a family pet or working dog will have a tough time running around with a sore knee. Dogs with a torn ACL are reluctant to play or go for walks. Exercise intolerance or poor athletic performance classically leads to weight gain, because pet owners never seem to decrease the amount of food (or are not told to do so). 7. Weight gain A consequence of many of the above changes is decreased activity, which invariably causes weight gain. This is a common observation in ACL patients. Unless the client decreases the dog’s food intake to match the decrease in activity, weight gain is inevitable. 8. Contralateral ACL tear Arguably, weight shifting may lead to a tear of the opposite ACL. While this might be manageable in a Yorkie or cocker, it becomes a much bigger problem with a Labrador or a mastiff. 9. Meniscal tear Instability in the knee can lead to a tear of the medial meniscus, causing even more pain (Figure 1). On the opposite, once the stifle is stabilized, the risk of a meniscal tear is minimized. 10. Distant problems The changes in gait and posture can affect all three other limbs, as well as the spine. Weight shifting may cause or exacerbate an orthopedic problem in another limb. “From a functional point of view, an ACL rupture is the beginning of a cascade of events in other body parts—joints, muscles—that we can’t forget,” said Laurie McCauley, DVM, CCRT, Dipl. ACVSMR, a rehabilitation specialist and owner of TOPS Veterinary Rehabilitation in Grayslake, Ill. One could argue that some of the above changes can be used to “date” an ACL tear. Let’s think about it: A patient with an acute ACL tear classically is lame and painful. A patient with chronic ACL disease typically presents with limping, pain, DJD, decreased range of motion, muscle atrophy and weight gain. In surgery, we certainly see much more osteophytes in a dog with a chronic tear than with an acute tear (Figure 2). From a surgeon’s standpoint, an ACL is a very fixable problem. Sure, it is possible to live with a torn ACL. Certainly, it might be the only option when the clients absolutely cannot afford surgery. ACL surgery has changed dramatically over the past few years. I now expect a return of at least 95 percent of normal function in a minimum of 95 percent of canine patients of any size after ACL surgery—whether it is performed with lateral nylon sutures, a TTA or a TPLO. So it’s hard for me to believe that affected dogs, especially large ones, have (and will have) a good quality of life with an untreated ACL tear. Dr. Phil Zeltzman is a board-certified veterinary surgeon and author. His traveling practice takes him all over eastern Pennsylvania and western New Jersey. You may visit his website at www.DrPhilZeltzman.com, and follow him at www.facebook.com/DrZeltzman. Zee Mahmood, a veterinary student at the St. Matthew’s School of Veterinary Medicine, contributed to this article.
