Cruciate ligament injury may well be better termed, "cruciate ligament disease." That's because veterinary scholars don't yet understand the true nature of this problem. In this very common disease process, the ligament that primarily serves to stabilize the knee joint breaks down (tears) or completely ruptures. This can occur with a sudden movement, as in a frisbee-dog, fast turn in the park--or via slow degeneration over time.
With a sudden (acute) injury, the dog was completely normal before the occurrence that let him to three-leg it home from the park. In the more common (chronic), slow-burn kind of ligament degeneration, symptoms may appear overnight or after a rough day out and about. But it's most likely been coming on for some time. In fact, most dogs with a cruciate ligament "injury" will display some evidence--minimal though it may be--of knee problems in the veterinary exam room before the average owner ever notices anything. Sometimes, both knees are affected--usually one more than another.
The cause of this problem? It's mostly genetic, we believe, though new studies are starting to favor the possibility of early spaying and neutering as a possible risk factor.
Symptoms and Identification
Acute cruciate ligament injury can be suddenly painful. But that pain and limping usually subside over a few days' time. Chronic cruciate ligament injury, on the other hand, will by slowly painful as the pet's body starts to lay down new bone to stabilize the ailing, painful knee joint. This is called arthritis (or, more appropriately, osteoarthritis) and its goal is to keep the knee from moving in a painful way.
Nonetheless, its presence leads ultimately to more pain, muscle loss over the affected knee's thigh--and, eventually, limping and difficulty rising.
Dogs (and sometimes cats) with underlying knee problems, such as medial patellar luxation (MPL) or previous trauma, are flagged for future cruciate ligament breakdown; the same goes for dogs of certain breeds (see below). Their owners should be advised of the possibility of future changes to this joint that may require surgical or long-term drug therapy in addition to the application of special rehabilitation techniques.
Giant, large and small breed dogs with medial patellar luxations (MPLs) are most often affected, but larger, mixed breed dogs and felines are not immune either. It is, however, considered rare in cats. The risk of CCL rupture is higher in certain breeds, such as:
Clearly, some breeds are far more prone to cruciate ligament injury/disease than others. In my experience, most clients are in denial about their pets' affected knees, especially when pain is not yet obvious to them. That's because pets don't show pain the same way we humans do. The kind of verbal complaints so common to humans just don't apply to our infinitely more stoic pets. But observant veterinarians will be able to identify a problem before owners do. After all, that's what veterinarians are there for, right?
Allow, as well, that middle aged to older pets are most likely affected, though I have seen pets with acute cruciate ligament injuries as young as 8 months of age.
Cruciate ligament injuries can be treated effectively, most commonly through surgery. Though ongoing pain relief through drugs, supplements, rehabilitation exercises and weight management are a necessary part of treatment, surgery is the mainstay of this process's management.
Here are the most common surgical techniques now employed:
TPLO (tibial plateau leveling osteotomy), TTO (tibial osteotomy) or another of the so-called, "leveling osteotomies": These procedures are currently considered the "gold standard" approach to surgical management of the cruciate ligament injury-affected patient who weighs over 25 pounds. With a TPLO or TTP, the knee is stabilized in a way that conforms to the normal weight-bearing stresses of the joint. A metal plate is inserted to achieve that newly-artificial balance. Dogs are usually back to almost-normal in six weeks.
Extra-capsular repair: This approach is still the most common procedure employed, though current thinking is sharply turning away from its effectiveness in dogs over 25 pounds. It works to stabilize the knee with suture material or artificial bands of material. It's at least as invasive as the TPLO or TTO and suffers from the effects of not stabilizing the knee joint with closer-to-normal mechanical stability.
The "TightRope": This is a currently popular technique that mimics the extra-capsular repair. It appears to be an improvement over the standard extra-capsular but has yet to convince board-certified surgeons and scholars of its approximation to the TPLO or TTO in terms of success rate--especially with respect to its use in larger-breed dogs.
In my experience, I've found that almost all cruciate ligament patients are best served by a board-certified veterinary surgeon. These professionals are best trained to determine the kind of procedure your pet needs. And by virtue of their unique training and experience, they also offer the greatest success rates when it comes to surgery in these cases.
Yes, it's expensive. Without a doubt, cruciate ligament surgery is pricey. More so (maybe double or triple) if you consider the use of a board-certified surgeon (always my preferred choice).
TPLO and TTO tends to go for about $2,000 to $3,000 per knee. Extra-capsular repairs by board-certified surgeons approximate $1,000 to $2,000, but I've seen some general practitioners offer this latter option for as low as $750.
Beyond surgery, a lifetime of pain-relieving medications and supplements has a way of adding up. Assume these will be required for all cruciate ligament injury cases:
Glucosamine and fatty acids are commonly recommended nutraceuticals (dietary supplements) for all pets with any kind of joint disease. They work to protect the cartilage in the joint.
Pet-specific anti-inflammatory medication like carprofen (Rimadyl) and meloxicam (Metacam) may also be prescribed.
As an adjunct to these, human opiates like tramadol (Ultram) may be in order.
Rehabilitation expenses should also be factored in. It's increasingly popular for pets who suffer cruciate ligament injuries to undergo extensive rehabilitation treatments. Because weight loss and muscle-building is so critical to the success of joint injuries and their resulting surgeries, rehabilitation medicine has emerged to treat your pets to the best in recovery services.
Many of us in the veterinary world are currently uncertain how to proceed. There's no available testing for genetic carriers of this condition. And because injury may be the only factor, it's especially confounding. In order to prevent cruciate injuries, do you treat your dog to a lifetime of inactivity to ward off any herding, frisbee-catching, agility-training sort of fun? I think not. Ultimately, activity and exercise is a plus. Avoiding it to avoid injury would be silly.
But there is a concern that breeders whose dogs have repeatedly encountered this problem in their dogs' offspring should take heed of the information and breed "around it." Also proposed in light of recent literature  is that some dogs (whose behavior and opportunity for inadvertent reproduction allow) should be left intact for up to two years of age, as this seems to reduce the incidence of cruciate injury. You should know though that this is controversial at the current time.
Whitehair JG, Vasseur PB, Willits NH. Epidemiology of cranial cruciate ligament rupture in dogs. J Am Vet Med Assoc 1993;203:1016-1019.
Duval JM, Budsberg SC, Flo GL, et al. Breed, sex, and body weight as risk factors for rupture of the cranial cruciate ligament in young dogs. J Am Vet Med Assoc 1999;215:811-814.
Wingfield C, Amis AA, Stead AC, et al. Comparison of the biomechanical properties of Rottweiler and racing greyhound cranial cruciate ligaments. J Small Anim Pract 2000;41:303-307.