Cruciate Conspiracy

Second Opinion
By Nick Trout, March 2011, Updated February 2015

A few years ago, the Wall Street Journal ran a story that they clearly felt blew the whistle on the “epidemic” of canine knee surgeries in this country: “The number of dog knees undergoing cruciate ligament repair each year in America is estimated to now exceed 1.2 million … Such treatments have helped fuel a doubling of the number of veterinary surgeons in the U.S. in the last decade …” Finger-pointing continued with mention of a scientific report that estimated that U.S. pet owners spent $1.32 billion to treat canine cruciate ligament problems.

It might just be me, but the story left me feeling like I spent my days drifting from one dog park to the next, trolling for customers—throwing Frisbees and tennis balls, attempting to induce knee injuries while doling out my business card.

Injury to the cranial cruciate ligament (or CCL, the equivalent of our ACL) has been recognized in dogs since 1926. This tough, strategically placed band of connective tissue lies within the knee joint and plays an essential role in stabilization. The bigger question is, why does CCL repair surgery appear to be more prevalent now?

The answer necessitates an understanding of what causes the problem, and here things get complicated. We know that certain breeds—including the Neapolitan Mastiff, Akita, Saint Bernard, Rottweiler, Mastiff, Newfoundland, Chesapeake Bay Retriever, Labrador Retriever and American Staffordshire Terrier—are at greater risk. (Vets are actively looking for predictors of cruciate disease, even identifying a genetic basis in Newfoundlands.*)


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We know that the problem frequently— 43 percent in one study— affects not one but both knees. We know that the majority of affected dogs are young (less than four years old). We know a CCL rupture or tear can be a traumatic injury sustained during vigorous exercise, but is more commonly precipitated by a minor event such as jumping, which suggests that an underlying weakness of the ligament has been brewing for some time. And then, there’s this weird relationship with sex (or maybe, lack of it). It doesn’t matter if the dog is male or female; the risk increases if he or she is neutered or spayed.

Lest you think there’s a veterinary conspiracy to generate more business, note that body weights of dogs with torn cruciate ligaments tend to be significantly greater than ideal. Sterilization can affect body weight, which, in turn, can a ffect activity. In other words, there are a myriad of interconnected predisposing factors for canine cruciate injury.

To my way of thinking, part of the perceived increase in the number of cases relates to a better appreciation of the disorder, earlier diagnosis and improved surgical options. While vets have been prone to blame canine lameness on hip dysplasia, a recent study showed that nearly one in three dogs referred to a veterinary teaching hospital with a diagnosis of hind-leg lameness actually had a torn cruciate. Our confidence in results obtained with procedures like tibial plateau leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA) has also made us more aggressive in our approach to dogs with partial cruciate tears. When people ask me why we don’t use a cheaper, more conventional repair, akin to a human ACL replacement, I point out an obvious disparity between us and our dogs. As two-legged upright creatures, we stand on a f lat knee joint in which, for the most part, the ACL has little to do, unless we participate in sports like skiing. On the other hand, our four-legged friends have their knees in a permanent state of fl exion—dogs are skiing all the time.

Granted, this is an oversimplifi ed analogy, but imagine visiting your orthopedic surgeon with a torn ACL and telling him, “I don’t mind how you fi x it, but I’m going skiing this afternoon and plan on hitting black diamond runs for the rest of my life.” I guarantee he would be looking for an alternative to a simple ligament replacement. That is exactly what has evolved for dogs.

So when a client with multiple dogs brings yet another patient with a torn CCL, and asks, “Is it me? Am I doing something wrong?” be assured that if I knew the answer, I’d blow the whistle. For now, my best recommendation is to keep your dog lean, provide him with regular exercise and, if you’re really paranoid, do your best to keep him on the canine equivalent of the bunny slope!

*Wilke V.L., Zhang S., Evans, R.B. et al. Identification
of chromosomal regions associated with cranial cruciate
ligament rupture in a population of Newfoundlands,
Am.J.Vet.Res. 2009; 70:1013–7.

Article first appeared in The Bark, Issue 63: Feb/March 2011

Nick Trout is a Diplomate of the American and European Colleges of Veterinary Surgeons and a staff surgeon at Angell Animal Medical Center in Boston.