Hip Dysplasia Susceptibility In Dogs May Be Underreported

[Jigsaw]

http://www.sciencedaily.com/releases/2010/...00902093454.htm

ScienceDaily (Sep. 2, 2010) — A study comparing a University of Pennsylvania method for evaluating a dog's susceptibility to hip dysplasia to the traditional American method has shown that 80 percent of dogs judged to be normal by the traditional method are actually at risk for developing osteoarthritis and hip dysplasia, according to the Penn method.

The results indicate that traditional scoring of radiographs that certify dogs for breeding underestimate their osteoarthritis susceptibility. The results are of clinical importance to several populations, most notably veterinarians, breeders and pet owners.

The two hip screening methods -- the standard Orthopedic Foundation for Animals, or OFA model, and Penn Vet's PennHIP model -- were applied to a sample of 439 dogs older than 2 years. The four most common breeds included in the study were German shepherds, Labrador retrievers, golden retrievers and Rottweilers, all breeds commonly susceptible to hip dysplasia.

According to Penn researchers, even if breeders were to selectively breed only those dogs having OFA-rated "excellent" hips -- the highest ranking but in some breeds, a very small gene pool, the study suggests that 52-100 percent of the progeny, depending on breed, would be susceptible to hip dysplasia based on the Penn Vet scoring method.

"We believe the lower rates of hip laxity detection using the OFA methods are not the fault of the expert radiologist reading the radiograph but rather a deficiency of the radiographic view," said veterinary surgeon Gail Smith, professor of orthopaedic surgery, lead author and director of the PennHIP Program. "We believe many veterinarians are not using the best test to control a disease. In many ways this is an animal-welfare issue."

The findings point to a weakness in current breeding practices. If breeders continue to select breeding candidates based upon traditional scores, then, according to the Penn study, breeders will continue to pair susceptible dogs and fail to improve hip quality in future generations. Despite well intentioned hip-screening programs to reduce the frequency of the disease, canine hip dysplasia continues to have a high prevalence worldwide with no studies showing a significant reduction in disease frequency using mass selection.

Canine hip dysplasia, or CHD, is defined by the radiographic presence of hip joint laxity or osteoarthritis with hip subluxation (laxity) early in life. A developmental disease of complex inheritance, it is one of the most common orthopaedic diseases in large and giant-breed dogs and causes pain and loss of mobility.

The traditional OFA screening method relies heavily on conventional hip-extended, or HE, radiographs, which the study contends do not provide critical information needed to accurately assess passive hip joint laxity and therefore osteoarthritis susceptibility.

"We suspect that all hip-screening systems worldwide based on the HE radiograph have similar diagnostic deficiencies," Smith said. "Hopefully, our results will motivate veterinarians and breeders to consider this newer approach."

To achieve genetic control of CHD, researchers said, an accurate test must minimize false-negative diagnoses which mistakenly permit the breeding of dogs that carry genes coding for CHD. Particularly for a late-onset disease such as CHD, dogs remaining in the gene pool must not only be free of obvious signs of CHD at the time of evaluation (2 years of age for OFA) but ideally should not be susceptible to the osteoarthritis of CHD that occurs later in life.

The PennHIP method quantifies hip laxity using the distraction index, or DI, metric which ranges from a low of .08 to greater than 1.5. Smaller numbers mean better hips. The PennHIP DI has been shown in several studies at multiple institutions to be closely associated with the risk of osteoarthritis and canine hip dysplasia. It can be measured as early as 16 weeks of age without harm to the puppy.

Specifically, the PennHIP method considers a DI of less than .3 to be the threshold below which there is a near zero risk to develop hip osteoarthritis later in life. In contrast, dogs having hip laxity with DI higher than .3 show increasing risk to develop hip osteoarthritis, earlier and more severely, as the DI increases.

Comparing the overall results of the study, 52 percent of OFA-rated "excellent," 82 percent of OFA-rated "good" and 94 percent of OFA-rated "fair" hips all fell above the PennHIP threshold of .3, making them all susceptible to the osteoarthritis of CHD though scored as "normal" by the OFA. Of the dogs the OFA scored as "dysplastic," all had hip laxity above the PennHIP threshold of .3, meaning there was agreement between the two methods on dogs showing CHD or the susceptibility to CHD.

The key feature of the PennHIP radiographic method is its ability to determine which dogs may be susceptible to osteoarthritis later in life. Because dogs are recognized as excellent models for hip osteoarthritis in humans, the authors are interested in the prospect of applying this technology to humans. Knowing a dog's risk for osteoarthritis early would allow veterinarians to prescribe proven preventive strategies, like weight loss, to lower the risk of this genetic disorder. Also, dog breeders now have a more informative measure to determine breeding quality to lower the risk of hip osteoarthritis in future generations of dogs.

"In humans, with appropriate studies of course, it is conceivable that mothers of susceptible children -- and there are many -- may adjust a child's lifestyle, including diet, to delay the onset or lessen the severity of this genetic condition," Smith said.

PennHIP is currently in common use by service-dog organizations such as the U.S. Air Force, the U.S. Army and numerous dog-guide schools. There are approximately 2,000 trained and certified members currently performing PennHIP procedure worldwide.

The study was conducted by Smith, Michelle Y. Powers, Georga T. Karbe, Thomas P. Gregor, Pamela McKelvie, William T. N. Culp and Hilary H. Fordyce of the Department of Clinical Studies at Penn Vet. Culp is currently with the School of Veterinary Medicine at the University of California, Davis.

The study was funded by the University of Pennsylvania, the National Institutes of Health, The Seeing Eye Inc., the Morris Animal Foundation and Nestle Purina Co. The article was published in the Journal of the American Veterinary Medical Association.

Smith, who is the inventor, and the University of Pennsylvania, which holds the patent, have a financial interest in the PennHIP method.

[sandgrubber]

How interesting, University of Pennsylvania finds their own method is better.

I wish they reported the correlation between clinical and radiographic finding . . . by either method.

[Staranais]

Pennhip is supposed to have higher heritability I believe, so if that's true it makes more sense to make breeding decisions based on Penhipp than OFA. My understanding is that the Penn system evaluates laxity & remodelling, whereas OFA just looks at remodelling. Bizarrely, there isn't necessarily a very good correlation between the results given by the two systems for any one dog.

Sandgrubber, I can post some links to good studies evaluating clinical signs & radiographs if you like, I have them saved on my computer, but they're not free to access. One of the studies looks at the swedish system (OFA type), and found that dogs assessed as moderate - severe HD at one year old had a much higher risk of claiming on their insurance policies for vet costs relating to HD later in life. Another study dissected out & examined the hips postmortem, and found that radiographs taken during life correlated well with the cartilage damage found in the hips after death.

[shortstep]

Business must be very slow at PENN. Nothing like beating your own drum. I see they fail to mention PENN is only a prediction and fail to mention you will still have to do an x-ray later to see if their prediction comes true. Not to mention that most dogs fall in the can't predict range anyway. No way I would switch over to PENN. And no way would I only select the very few dogs with the best DI to breed, this would be devastating in decreasing the gene pool (there by increasing the risk of other problems) for most breeds.

The current DNA research is already proving that 'scoring' parents hips by either/any method is never going to be the end all in preventing HD in litters of pups. With at least several genes directly involved and several more traits/tendencies indirectly involved, not to mention environment and nutrition, prediction is going to be difficult until we have at least some form of DNA test and even then it will likely still not predict if the dog can produce it in their pups.

http://www.stilhope.com/hipartical.htm

Here is a article that compares PENN to some other methods, and what this shows is PENN is very breed specific and not as accurate on all breeds, also examines some of the pitfalls of PENN prediction.

At then end they mention a new method to look at hips, which is now available see http://bakerinstitute.vet.cornell.edu/facu...page.php?id=197

This test which is done at 8 months is also compared to PENN and is more accurate in predicting HD.

Latest work at Cornell...

'We have identified chromosomal regions harboring the genes that confer susceptibility to, and protect against, canine hip dysplasia. We have discovered several markers (single nucleotide polymorphisms) that predict a dog's breeding value or genetic potential for hip conformation. We are validating these markers. '

This is very exciting news and the gossip is that in a few years we will have some sort of DNA tests.

This link will take you to links to most of the work they are currently doing.

http://web.search.cornell.edu/search?outpu...splasia%20genes

[Stolzseinrotts]

I agree with shortsep.........I would not be changing over for the reasons mentioned.

I am not a fan of OFA either. It has been proven here that a dog that was OFA fair was rescored here at 5 years of age and under our system used here the dog scored 2.2 which should be an OFA Excellent. I like our system as it scores all areas and shows you were there are changes, thus IMO giving you a more accurate scoring and therefore picture of the hip status.

I will stick with the system we have I think it is great!

Off Topic a bit

I will add that I have had a couple of dogs owned by me but living elsewhere radiographed by a Penn Hip Vet for the standard HD scoring used for Rottweilers and the positioning was bloody awful on one and the Vet was upset because I was not happy with it! Go figure...bad positioning equals higher score which was exactly what happened in this case with one of the dogs and the reason I was not happy at all. We only get one shot at our scores unless it is marked on the paperwork that the positioning affects the scores. Sad thing is these were all done digitally and I can't get a copy of the email that stated the positioning was poor so I am stuck with a score that I am not happy with due to poor positioning which blind freddy can see on the images.

[sandgrubber]

Thanks for the offer. At $35/pop or so, I'm unlikely to read more than the abstracts, especially as my stock has no hip problems but occasional elbow problems that seem to come out of the blue.

Good to know the studies have been done.

Some one else may be interested in references, though. With us all putting so much emphasis on hip and elbow scores in breeding programs, it's reassuring to know that poor scores are a useful predictor of later life health problems.

Sandgrubber, I can post some links to good studies evaluating clinical signs & radiographs if you like, I have them saved on my computer, but they're not free to access. One of the studies looks at the swedish system (OFA type), and found that dogs assessed as moderate - severe HD at one year old had a much higher risk of claiming on their insurance policies for vet costs relating to HD later in life. Another study dissected out & examined the hips postmortem, and found that radiographs taken during life correlated well with the cartilage damage found in the hips after death.

Edited September 4, 2010 by sandgrubber

[shortstep]

I'm unlikely to read more than the abstracts, especially as my stock has no hip problems

Sandgrubber,

Congratulations on having a line of Labs with no HD problems!

You really should let some of the research teams know you have line of labs free of HD disease. They really need to look at what you have done to accomplish this and the genetics of your dogs. Your dogs could hold the genetic key for HD free dogs of all breeds.

Cornell is using Labs right now in the search for genes. However the Labs are used as the affected line not the line free of HD genetics. They are using a different breed for the line that does not carry the genes. Usinfg 2 different breeds makes it harder to find the genes. I am sure your HD free labs would prove very valuable in their research.

[sandgrubber]

What do they consider HD free. The worst I've gotten for a dog of my lines raised on my property is 3:1 . . . which I consider to be a non-problem, though not perfect.

In my experience, there are quite a few Lab lines that run low hip scores.

Lab averages are not that bad compared to other breeds . . . I don't know why they have a reputation for bad hips.

I'm unlikely to read more than the abstracts, especially as my stock has no hip problems

Sandgrubber,

Congratulations on having a line of Labs with no HD problems!

You really should let some of the research teams know you have line of labs free of HD disease. They really need to look at what you have done to accomplish this and the genetics of your dogs. Your dogs could hold the genetic key for HD free dogs of all breeds.

Cornell is using Labs right now in the search for genes. However the Labs are used as the affected line not the line free of HD genetics. They are using a different breed for the line that does not carry the genes. Usinfg 2 different breeds makes it harder to find the genes. I am sure your HD free labs would prove very valuable in their research.