Part III-Follow up on OFA vs. PennHip By Ann Allen
I have read dozens of articles and several books on canine hip dysplasia (CHD) to prepare for the two articles that I wrote for the AKC Gazette columns of October 2006 and January 2007. The topic of CHD is a giant one to say the least and studies suggest all kinds of conflicting interpretations of the current methods of evaluation. There is even plenty of mud-slinging by both camps -OFA and PennHip- to discredit each other’s methods and to further confuse those trying to make the best decisions possible when it comes to hip clearances. The Griffon appears to be in relatively good shape compared to other breeds based on both OFA and PennHip statistics. With a smaller gene pool it is probably easier for breeders to track down those dogs that seem to be carriers or what breeding combinations appear to yield more cases of CHD than others. I have heard many stories from various breeders over the years about disappointing outcomes of a breeding that on paper appeared to be very sound based on health clearances. One breeder told me that when she doubled back to dog X, she got dysplastic pups even though there was no evidence of CHD in either dam or sire’s pedigree. Another told me that when using one sire in combination with dams in a particular line, he got dysplastic pups. Breeding is not an exact science, that is for certain.
Without identification of the precise genes that contribute to CHD, we are left with those methods we currently have on hand to help us make the best breeding decisions. Most breeders currently use the OFA hip-extended view method. There are many advantages to using this system. It is cheaper, does not require anesthesia and the results are compiled into a database for anyone to access through the OFA website. Results are very easy to understand with gradings of Excellent, Good and Fair assigned to dogs certified free of hip dysplasia. But, there are also disadvantages to this system.
First, one of the biggest criticisms of the OFA method, is that submission of x-rays to OFA for evaluation is completely voluntary. Owners may opt to submit an evaluation but not to have results published. (Submitted, but unpublished results are, however, factored into the database according to the OFA.) A breeder’s veterinarian may look at a set of x-rays and suggest to them that they will not pass so they are not sent in. I know of many people who have not submitted x-rays simply because their vet said they didn’t look very good and have even heard of dogs being euthanized based on this opinion alone. Not submitting x-rays based on the opinion of a veterinarian who might have limited orthopedic or radiological expertise does the breed a huge disservice. All x-rays should be submitted to the OFA for public disclosure, no matter what! To not submit x-rays or to not allow publication of results for whatever reason hides the facts about our breed’s health rather than doing the right thing by publicly disclosing where there may be potential problems in the breed so that everyone may benefit from this information. I commend those breeders and Griffon owners who have gone public with their disappointing OFA results!
Second, the OFA method provides a limited evaluation of the hip’s structure. For example, an OFA rating of “Good” says nothing more than, at the time the radiograph was taken, the structure of the hip did not show CHD. OFA describes a Good hip as “slightly less than superior but a well-formed congruent hip joint is visualized. The ball fits well into the socket and good coverage is present.” The hip-extended radiographic view only looks at the current structure of the hip joint itself determining how well the ball fits into the socket. It is no insurance that the joint will not deteriorate later in the dog’s lifetime. It also does not predict the likelihood that the joint may develop CHD in the future and it is based solely on the subjective opinion of a team of veterinary radiologists. Some studies suggest that there is great variation and inconsistency in the grades assigned by the OFA radiologists even with x-rays resubmitted to the OFA.
If the joint shows some deterioration, remodeling of the bone, arthritis or malformation of the ball or socket, there is already evidence of CHD. Dr. Greg Keller of the OFA suggested in a recent interview that Fair rated Griffons should probably not be bred given the high distribution of Good and Excellent Griffons (21% Excellent, 61.9% Good) in the evaluation pool that breeders have to choose from. Why breed to the bottom of the barrel when we are blessed with so many better specimens? An OFA rating of Fair is still certified free of CHD. According to OFA, Fair is “assigned where minor irregularities in the hip joint exist. The hip joint is wider than a good hip phenotype. This is due to the ball slightly slipping out of the socket causing a minor degree of joint incongruency. There may also be slight inward deviation of the weight-bearing surface of the socket (dorsal acetabular rim) causing the socket to appear slightly shallow.” Doesn’t this description already suggest a malformed joint, slight though it may be? Why breed a dog that has a ball slipping out of the socket? The point is, if there is evidence of CHD of any degree, that dog is probably a carrier of CHD. As Dr. Keller pointed out in the same interview, “It is important to understand that heritability estimates do not refer to the degree of inheritance but rather to the degree that the added genetic component is reflected in phenotype.” Even though HD may only be slightly reflected in a Fair joint, isn’t the genetic component still there? Isn’t a dog still going to pass on these bad genes? We aren’t going to improve our breed if these are the kinds of decisions we make in our breeding programs. We need to stop breeding Griffons with Fair hips or with Fair hips in its pedigree.
Another problem with the OFA method is that studies suggest that the standard hip-extended radiographic view masks the true laxity of the hip. When extending the dog’s legs downward in order to get the hip-extended view for x-ray purposes, the hip joint is actually wound up more tightly than if it were in a natural, standing position. PennHip’s research is more focused on the laxity of the hip joint, in other words, how tightly the joint is held together. It would be logical to assume that a loose joint’s ball would not fit well into the socket and by sliding around, produce the kinds of remodeling of the joint bones and deterioration of the hip joint as seen in OFA ratings of Fair, borderline, mild or severely dysplastic evaluations. Both OFA and PennHip seem to concur more on the low end of OFA evaluations.
It is the OFA Good and Excellent evaluations that are called into question for they may give breeders a false sense of security. While these evaluations do not show obvious evidence of joint deterioration at the time of the x-ray, they do not necessarily show how tight a joint is. By winding up the joint for the hip-extended radiographic view, looseness is not observed in these x-rays. OFA merely offers a snapshot view of hips at the time of the x-ray. If the hips do not show signs of CHD they are given the stamp of approval as “certified clear of CHD”. However, this snapshot cannot predict the statistical likelihood that a given dog will develop CHD at a later date.
There are currently limited studies comparing the OFA Good or Excellent evaluations to PennHip’s distraction index results. I have read the evaluations of one Griffon with both OFA and PennHip evaluations. OFA rated the dog’s hips Good while the PennHip evaluation showed this dog’s hips to be among the tightest in the entire PennHip Griffon evaluation pool. I also know of one Griffon bitch that received an OFA preliminary evaluation of Good and later turned out to have extreme laxity of the hip joints from PennHip with both hips having a distraction index of above .70, thus being at high risk of developing CHD. (See distraction index explanation below.) If breeders are given the OFA’s stamp of approval for breeding a dog with supposedly clear hips, think of the potential for disaster in our breed’s future given this last scenario. One has to wonder how many of our breeding Griffons have also been given a similar, misleading green light for breeding. It is impossible to know how many of these false negatives are bred, but if we are unwittingly breeding what we are lead to believe are healthy Griffons, we will never eradicate CHD.
The PennHip evaluation is comparatively new to Griffon breeders. It does use, just as OFA does, the standard hip extended view to check for the existence of CHD in the hip joint. But, the other two radiographic views provide additional information about the hip’s laxity, the key contributor and predictor, according to PennHip, to CHD.The compression view is used for evaluating how well the femoral head (ball) and the acetabulum (socket) fit together. The distraction view gives an objective, quantitative measurement of how far the femoral head can be distracted, or forced out of the socket and it compares this measurement to other dogs of the same breed. The PennHip radiographic procedure is very different from the OFA procedure in that only a PennHip certified vet can perform the procedure after attending specific training suggesting better consistency in x-ray technique. Any veterinarian can perform the OFA procedure. In the PennHip procedure, general anesthetic is required, a factor that adds to the cost of the procedure. The additional two radiographic views also add to the total cost ranging between $200-$500 depending upon the area in which you live. PennHip claims that all x-ray submissions are mandatory by those vets certified to perform the x-ray procedure thus rendering the results more accurate than the OFA voluntary submission.
The following is the semi-annual laxity profile update as of September 2006, the most recent profile for the Wirehaired Pointing Griffon:
Number of Wirehaired Pointing Griffons: 159
Minimum DI*: 0.20
Maximum DI*: 0.88
Mean (average) DI*: 0.43
50th% percentile**: 0.39
60th% percentile**: 0.36
*DI = Distraction Index is a measurement of the amount of maximal passive hip laxity. A low DI indicates a small amount of laxity or a "tight" hip, while a high DI indicates a "loose" hip. Dogs with tight hips, DI's less than or equal to 0.30, are at extremely low risk for developing degenerative joint disease (hip dysplasia). As the DI increases, the hip is more likely to develop DJD (degenerative joint disease). Dogs with DI's that are 0.70 and above are considered to be at high risk for developing hip dysplasia.
**Percentiles = A quantification that allows an individual dog to be compared to other individuals of the same breed. When considering percentiles, 50% is average and 60-100% is above average. A dog in the 80th percentile, for example, would be tighter than at least 80% of the group of dogs in the database. Note with percentiles, the higher the number, the better (opposite of the DI, where the higher the number the more likely the hips are to develop DJD.
The PennHip method is not without its problems. First, its database is not open to the public except for general breed statistics. A breeder cannot learn the distraction index of a dog s/he is interested in breeding to nor that of any of its relatives for comparison through PennHip. The database is supposedly updated semi-annually. I can tell you that the Griffon database was not updated between October 2005 and September 2006. While PennHip data tells me something about my own dog, it tells me nothing about any one else’s and does not allow me to learn about trends in a given breeding line or from a popular stud or bitch. Furthermore, a database of only 159 dogs does not tell me enough about our breed as a whole when compared to a database ten times as large. I would be much more interested in a public database of individual dogs.
Second, the OFA contends that joint laxity, PennHip’s primary focus for evaluation, is considered to be one of the earliest pathologic findings of CHD but is not the only factor. They argue that even dogs that may “demonstrate abnormal laxity do not develop the definitive degenerative changes of dysplasia.” They also believe that the specific degree of laxity acceptable at a given age or in a given breed has not been determined. The OFA argues that the use of artificially forced laxity to measure the amount a hip can be forced out of the joint, as in the distraction portion of the evaluation where the veterinarian manually forces the hips out of the socket, is performed in an unnatural, non-weight bearing position on the dog. They believe the test would be more accurate if the technique were able to measure laxity that occurs when a dog is in a more normal, standing position. In other words, the OFA believes that there is further research necessary in order to understand the full implications of joint laxity as a component of the development of CHD.
Third, the Wirehaired Pointing Griffon Club of America, WPGCA, is now requiring that all its breeding stock and offspring have Penn Hip evaluations. The WPGCA-registered “Griffon’s” results are also being thrown into the purebred Griffon’s statistics. This provides inaccurate statistics considering that they are not purebred Griffons and come from a different breed’s genetic stock. We currently have no way of knowing, without access to the PennHip database, which of the 159 dogs are purebred or Griffon-Ceszky Fousek crosses. This is an issue the AWPGA is addressing with PennHip. At least in the public OFA database, the GRB prefix indicating the mixes under the registration separates them from the purebreds that are indicated as GR.
Finally, until we have a definitive genetic test for the multiple genes that contribute to CHD, we have not yet heard the final answer in determining the best way to evaluate breeding stock. What we do have are two different systems for looking at the phenotypic and suggested genotypic quality of the dog’s hips. There are also other factors to take into consideration that can contribute to CHD such as diet in growing puppies, physical activity and inactivity and injury among them.
I think the PennHip system is a more accurate system of evaluation of our dog’s hips. It is a system that uses objective data to statistically predict the likelihood that a dog will develop CHD based on the laxity and structure of the hip. In his outstanding presentation at this year’s AWPGA National Specialty in Arkansas, John O. Lewis, DVM suggested that we breed Griffons with the tightest hips, that is, those Griffons with the lowest Distraction Index and with a Distraction Index lower than the mean. The current mean DI for the Griffon is .43. Keep in mind that PennHip studies suggest that dogs with DI's less than or equal to 0.30, are at extremely low risk for developing degenerative joint disease (canine hip dysplasia). We need to have more Griffons evaluated by PennHip in order to have a clearer sense of which dogs are superior for a breeding program. I would also like to see the AWPGA collect PennHip data from all Griffons whose hips have been evaluated and have that information readily available to the public, perhaps for quarterly publication in the Griffonnier, just as the OFA reports are published.
In the end, it may be to our advantage to have our breeding Griffons evaluated by both OFA and PennHip since there are advantages of both. This can easily be done in one office visit to the vet since the standard hip-extended view used by the OFA is one of the three views used in the PennHip evaluation. It would also allow breeders additional information in the case of what might appear to be conflicting results, i.e. OFA Good vs. a high PennHip DI. The more information we have on our dog’s hips, the better. Let’s seek out those dogs with the tightest hips, the best conformation, hunting ability and temperament to produce the best all around Wirehaired Pointing Griffons.