In a recent article concerning an herbal product used for treatment of a dog with a ruptured cranial cruciate ligament (the equivalent of the “ACL” in humans), I stated, “Surgery is the treatment of choice for a ruptured cruciate ligament. Weight loss, physical therapy, and possibly medications are all helpful and important, but without surgery a large dog will have permanent instability in the knee and will develop progressive arthritis.” One of my regular readers challenged this statement and referred to evidence in humans suggesting that surgical therapy was no better than non-surgical therapy in treating this disease. This stimulated me to look into my assumption that surgery was superior to medical management for large dogs and see whether or not the evidence supports this claim.
Following the usual approach I take in evaluating a proposed therapy, I will look at the plausibility of the intervention first. A great deal has been written about the biomechanics of the canine knee and all the factors that may play a role in cruciate ligament ruptures (e.g. 1, 2, 3, 4, 5, 6, 7, 8). The bottom line of all this is that ruptures of the ligament are caused by multiple interacting factors including breed (and hence genetic influences), size, the structure of the canine knee, and activity. The various surgical procedures recommended for this disease are all rational and plausible based on a detailed understanding of the basic biomechanics of the disease.
There have also been many studies looking at the effect of various surgical procedures in animal models of the disease, usually laboratory dogs with ligaments that have been deliberately damaged. While this sort of model does not replicate all the features of naturally occurring disease, it can provide some clue as to whether the surgical therapies are likely to be effective. These sorts of studies, often used as models for arthritis in general, show clearly that severe joint disease and marked dysfunction results over time without surgical treatment of a ruptured cruciate ligament (e.g. 9, 10, 11, 12, 13, 14, 15)
There is extensive clinical research in humans concerning whether surgical repair of cruciate ligament rupture is necessary. I am quite skeptical of the applicability of this research to the same question in dogs since the biomechanics of the canine knee are quite different from those of the human knee. Also, conservative management for humans includes exercise restriction, physical therapy, and often immobilization of the knee with a brace, all of which are challenging and not often used in dogs with ruptured cruciate ligaments. However, the basic anatomy and pathophysiology of arthritis are quite similar, so research in humans may have some value in answering the question for dogs.
The results of clinical trials in humans are mixed. One Cochrane Review examining older surgical techniques found they were generally superior to conservative management. Some studies have found no advantage to surgical management, but these are not large or methodologically robust trials. It appears that both conservative and surgical management can have good outcomes, but the differences depend on the patient population (age, nature of injury, activity level, compliance with treatment, etc) and the specific therapy employed, so not incontrovertible conclusion can be made as to whether surgery or conservative management is superior overall.
There are a many studies looking at the outcome of surgical treatment of cruciate ruptures in dogs. Overall, they find good outcomes in the range of 70-80% or more of patients returning to normal or near normal function (e.g. 16, 17, 18, 19). Comparisons of different methods of surgical repair do not support the clear superiority of one method. However, there are few studies directly comparing surgical and non-surgical treatment in dogs. The best of these, published in 1984, compared outcomes of non-surgical treatment in dogs weighing more or less than 15kg (about 30lbs). For the dogs over 15kg, only 19% were normal (7%) or improved (12%) years after their injury, and all had clear evidence of severe arthritis in the affected knee. For dogs weighing less than 15kg, almost 86% were normal (75%) or improved (11), and while all of these had evidence of moderate arthritis, it did not seem to affect the function of most of these dogs. Other less rigorous studies have the same general findings (20, Paatsama S: Ligament Injuries of the Canine Stifle Joint: A Clinical and Experimental Study. Master’s thesis, Helsinki, 1952)
As is almost always the case, the evidence is not of the highest possible quality or unequivocal, but this does not exempt us from having to draw conclusions and make recommendations to our clients. My interpretation of the available evidence is that overall, cruciate ligament disease causes significant arthritis and loss of function when untreated. For most dogs under 15kg, conservative management (primarily restricted activity for 3-6 weeks, achieving and maintaining and appropriate body weight, and possibly physical therapy and pain medication) can achieve acceptable comfort and function. In larger dogs, significant arthritis is inevitable and dysfunction is extremely likely without surgical treatment. No single surgical technique is clearly superior, so the choice of specific surgery should be determined by the judgment of the individual surgeon and the needs of the owner.