A 2-year old dog with severe hip arthritis due to CHD
As a veterinarian, few conditions frustrate me more than Canine Hip Dysplasia (CHD). This is not because there are not ways of treating it. In fact, there are plenty. A multitude of NSAIDs (non-steroidal-anti-inflammatory-drugs) are available to manage it medically and for more severe cases, there are many surgical options. My frustration stems from our failure to prevent it in spite of having the means to do so.
For anyone who is not familiar with CHD, it is a genetic disease that results in loose hips. Dogs with the condition have hip joints in which the "ball" of the "ball-in-socket" hip joint does not fit tightly into the "socket". Over time, this instability results in inflammation, arthritis and pain, resulting in many dogs of large breeds being essentially hobbled-up before they reach three years of age.
And here's what gets my goat: there is absolutely no reason that so many dogs should still be suffering through the pain of CHD and that so many dog owners should be suffering through the expense of treating it. We humans are in charge of which dogs get bred and we have at our disposal the means to identify and breed only those dogs with the best hips. When this is done, less CHD is passed down to future generations of dogs, and the quality of life of our canine companions will improve. CHD should be rare yet instead it is common.
So what gives? First of all, there unfortunately are plenty of breeders who breed dogs with nary a concern for hip health (I'm talking to you puppy millers!) Our only hope is to appeal to them through outreach and education. More embarrassing is the failure of people who should know better-vets and well-intentioned breeders-to prevent the disease. This is because of a dogmatic adherence-by many vets, breeders and breed clubs-to an outdated method of hip evaluation: the Orthopedic Foundation for Animals or OFA method.
When an OFA evaluation is done, a potential breeding dog is anesthetized and placed on his back on the x-ray table. The legs are extended so that they are parallel to the spine and the image is taken. The resulting image is then sent to the OFA and reviewed by three individual radiologists whom each assign a very subjective rating of poor, fair, good or excellent based upon visual inspection alone. Then, following a very arbitrary algorithm, a final average rating is given to the hips.
There are several problems with this means of evaluating hips. First of all, when the hips are positioned in that unnatural, hyper-extended position, the soft tissue that supports the hip joints winds up like a rubber band and actually forces "the ball" of the hip, deeper into "the socket". This makes the hips seem "tighter" than they would be if the dog was standing normally. Secondly, because nothing is objectively measured or quantified in the OFA process, the rating given is nothing more than an "average" of three subjective opinions. Finally, there is no correlation between having an "excellent" OFA rating and a dog not developing osteoarthritis. In fact, many OFA excellent-rated dogs are known to develop arthritis as they age.
A by far better means of identifying at-risk breeding dogs is the University of Pennsylvania Hip Improvement Program or PennHIP method. PennHIP is superior to OFA because it does quantify the amount of "looseness" in a given hip. Knowing exactly the amount of looseness in a breeding dog's hips and being able to compare it to the amount of looseness in potential mates is much more useful information for breeders. This allows them to choose for breeding only those dogs with the "tightest" hips and subsequent generations of dogs will be at much lower risk for CHD.
Developed by Veterinary researcher Dr Gail Smith at the University of Pennsylvania, the PennHIP method quantifies the amount of "looseness" in a given hip joint into a value called the Distraction Index (DI). Using a device called a distractor, a PennHIP-certified vet X-rays the dog anesthetized and on his back, but with the legs in their natural perpendicular position with respect to the spine. One X-ray is taken with the "balls" of the hip joint compressed into the sockets. This calibrates the hips to their zero point. Then three x-rays are taken in the same position but using the distractor. The distractor gently displaces the balls away from the sockets, demonstrating the amount of natural looseness in a breeding candidates hips. A final X-ray of the OFA-style hip-extended view is taken because the one bit of useful information it provides is whether or not arthritis is forming.
The DI is the distance the balls displace away from the socket divided by their radius and it is a number that carries with it a lot of useful info. First of all, any dog with a DI of less than 0.3 has virtually no chance of developing arthritis. The higher the DI is above 0.3, the higher the risk of developing arthritis. (Interestingly, nearly all Greyhounds have a very low DI and CHD is unheard of in this breed. Apparently selecting only the fastest dogs for breeding carried with it the added benefit of selecting for very tight hips. This makes sense because a dog with loose hips can't win races.)
Secondly, the breeder can see where her dog's DI value is with respect to other dogs of the same breed that have also had a PennHIP evaluation. If her dog's DI values are above 0.3 but fall within the tighter half of the bell curve for the breed then her dog is a good candidate, with respect to the trait of hip looseness, for breeding. Furthermore, she can find a mate for her dog that also has a decent DI the result being puppies with healthier hips.
It is time for the OFA method to be abandoned in favor of PennHIP. Too many dogs are suffering. The good news is that PennHIP is slowly catching on. Every year more and more breeders are choosing it over OFA. Perhaps someday, CHD will be as rare as Distemper. One can only hope.
Mike Bukowski DVM 1/24/2012