Owner and Breeder Questions
Q. My dog was bred unexpectedly before she had the PennHIP procedure done, and had her pups 1 week ago.  How long after the dog gives birth should I wait until I can have her PennHIPed and get a true reading?
Q. Our population is small in bloodlines but I am worried to use the 0.50. I understand the possibility of developing HD is much bigger with the 0.50. Do you know what breed clubs in other country's use for breed standard with PennHIP?
Q. On the hip evaluation report there is the following sentence; "Please note that the PennHIP DI is a measure of hip joint laxity, it does not allude to a passing or failing hip score." If the DI isn’t, then what is?
Q. In our breed club we use 0.40 or lower to breed with that dog. It’s the median DI for our breed. In your opinion is this too high or too low?
Q. If my dog has a PennHIP evaluation at a newly PennHIP certified veterinarian, instead of one who has been doing the procedure for over a year, should I be worried that my dog’s laxity will be different with the less experienced veterinarian?
Q. How does the increased number of dogs of my breed affect my dog's percentile?
Q. What does the DI (Distraction Index) actually predict?
Q. Is this still accurate - 'is accurate in puppies as young as 16 weeks of age'?
Q. Is a certain amount of flattening of the heads allowed or must they be perfectly rounded?


Q. My dog was bred unexpectedly before she had the PennHIP procedure done, and had her pups 1 week ago.  How long after the dog gives birth should I wait until I can have her PennHIPed and get a true reading?
A. We do not recommend a PennHIP evaluation close to whelping or up to 1 month following the end of lactation. During the birthing process, a hormone called relaxin is released, which causes overall relaxation of muscles and other tissues, and mayinclude the joint capsule. This would potentially cause that dog’s hips to appear more lax than they actually are.

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Q. Our population is small in bloodlines but I am worried to use the 0.50. I understand the possibility of developing HD is much bigger with the 0.50. Do you know what breed clubs in other country's use for breed standard with PennHIP?
A. It is correct the higher the DI (ie. the more lax the hips are) the more the hip dysplasia susceptibility increases. For example, a dog with a DI of 0.9 is much more likely to develop hip dysplasia (and sooner) than a dog with a DI of 0.48. In addition, the median DI for each breed varies. We update the breed statistics twice per year. At this time the breed mean for German Shepherds in general is 0.43, but 6 months or a year from now it may change. For this reason it is probably not a good idea to decide on a specific DI value as being a breed standard (unless of course, the DI is < 0.3). Instead, use the 60th-100th percentiles as a guide. This ‘breeding interval’ will correspond to tighter and tighter hips (better DI’s) as selection pressure is applied over generations.

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Q. On the hip evaluation report there is the following sentence; "Please note that the PennHIP DI is a measure of hip joint laxity, it does not allude to a passing or failing hip score." If the DI isn’t, then what is?
A. Since hip laxity is inherited in a polygenic manner, and different combinations of unwanted genes can result in a wide range of outcomes, a "pass-fail" system, as used by the OFA is simply not appropriate. Since the OFA system has been in use for the past 38 years, many people are accustomed to a "pass-fail" mentality and we are often asked about this at PennHIP. The DI itself can vary continuously and each breed has a unique susceptibility to arthritis as a function of the DI values (Smith GK, Mayhew PD, Kapatkin AS, et. al., 2001). Therefore susceptibility to hip arthritis depends on specific breed statistics, for example the mean and the distribution of laxity within each breed. A dog with a DI in the 60th-100th percentile would be considered a good breeding dog, producing genetic improvement in subsequent generations. But such a dog would not be technically normal unless its DI is less than 0.3. So it may be suitable for breeding but still be susceptible to hip dysplasia and therefore not “normal”. The goal of PennHIP is to drive all DIs for each breed below 0.3, into the unsusceptible range.

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Q. In our breed club we use 0.40 or lower to breed with that dog. It’s the median DI for our breed. In your opinion is this too high or too low?
A. The goal is to drive the DI for each dog within a breed below 0.3, in the unsusceptible range. This will happen if dogs between the 60th-100th percentiles are used for breeding, since these are dogs that, if bred, will result in positive genetic change for the better. Of course, if you breed two 90th percentile dogs, much faster genetic change will occur compared to two 60th percentile dogs. Breeding dogs in the 50th percentile or mean, would not result in positive genetic change in the next generation.

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Q. If my dog has a PennHIP evaluation at a newly PennHIP certified veterinarian, instead of one who has been doing the procedure for over a year, should I be worried that my dog’s laxity will be different with the less experienced veterinarian?
A. The mechanical behavior mentioned in the above question explains the observed repeatability of the PennHIP procedure. Specifically, the PennHIP method has been statistically proven to be consistent and reliable when evaluated within and between examiners (Smith GK, LaFond E, Gregor TP, et.al., 1997). This published study compared repeatability of the distraction index measurements between inexperienced examiners (not certified and just learning the technique) and experienced (PennHIP certified) examiners as well as compared the measurements within examiners. From this study, it was shown that the repeatability and clinical reliability was statistically high for within and between examiners, and can be considered interchangeable based on a high intra-correlation coefficient. Remember that there will be biologic variation with any test over time, such as blood pressure, so the DI during one exam may not be exactly the same as during an exam at a subsequent time, but the laxity measured will be statistically comparable.

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Q. My dog was Penn Hipped in 2001. At that time, less than 500 of our breed had participated in PennHIP. My dog was in the 90th percentile at that time. I would imagine that many more of our breed have had PennHIP evaluations by now. How does the increased number of dogs of my breed affect my dog's percentile?
A. Let's use the analogy of flipping a coin. If a coin is flipped 10 times and you count the number of heads and tails, you would most likely get a percentile that is not exactly 50%. However, the more times the coin is flipped, the more the percentage of heads and tails will converge to 50%. In the case of your breed, 500 is a very large number for statistical breed calculations, and I wouldn’t expect the actual breed mean to change substantially if more dogs were included in the calculation. However, if many breeders are aggressively breeding for tighter hips, this would gradually drive the mean breed DI down over time (a very desirable outcome). If you would like an updated hip laxity report, a new report can be re-issued at a cost of $5 which compares your dog’s previous PennHIP DI to the current breed statistics.

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Q. What does the DI (Distraction Index) actually predict?
A. The DI can tell you if a dog is at risk for hip dysplasia. A dog with a DI below 0.3, based on our research for all breeds in general, has almost no risk of developing hip dysplasia (osteoarthritis) in that hip. There may be different thresholds for each breed. For example, German Shepherds are more susceptible to hip dysplasia than other common breeds of dogs, and thus may have a lower threshold than 0.3 to be free of susceptibility to arthritis. A higher DI indicates more hip laxity. Since hip laxity (as measured by the PennHIP method) has been identified as a risk factor for hip dysplasia, the higher the DI, above 0.3, the higher the risk is for hip dysplasia. This means that a dog with a DI of 0.8 would have a much greater risk of hip dysplasia than a dog with a DI of 0.46. A DI of 0.8 also means that the femoral head can be subluxated 80% out of the socket; a 0.46 would be 46%. Note: These are not the percentages used for the percentile rankings, below.
      Percentiles are a quantification used to compare that specific dog to the rest of the breed, and are based on the looser hip (ie. higher DI). When considering percentiles, 50% is average and 60-100% is above average. A dog with a DI in the 50th percentile has hip laxity approximately equivalent to the average of the entire breed. A dog with a DI in the 70th percentile means that the dog’s hips are better than 70% of the rest of the breed. The higher the percentile, the lower the DI, which means they are less prone to the onset of hip dysplasia. So it would be better to adopt a 70th percentile dog over a 50th percentile as far as hip status goes. Dogs with a DI in the 60th-100th percentile represent good breeding dogs, resulting in genetic change for the better in subsequent generations, because they carry more genes for good hips. In some breeds, dogs with a DI of 0.3 or less are very difficult to find, but remember that tighter hips are better hips, so purchase the dog with the tighest hips you can find.
      The most accurate PennHIP result, based on our studies, can be obtained at 1 year of age. Pups can be evaluated as early as 16 weeks to give an idea of what hip status is like when breeders make the first cut for breeding decisions. But we recommend a follow-up PennHIP at 6 months to 1 year of age, or later. If the dog was in the 70th percentile at 16 weeks of age, the DI could change somewhat if repeated at an older age, since pups are still growing rapidly at that age.
      When considering dogs susceptible to hip dysplasia, studies have shown that keeping dogs thin is the best way to delay or possibly even prevent the onset of hip osteoarthritis. Lean dogs also live longer. So this means even if the dog is in the susceptible range (DI > 0.3), he will definitely benefit if kept thin for life.

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Q. Is this still accurate - 'is accurate in puppies as young as 16 weeks of age'?
A. Pups can be evaluated as early as 16 weeks to give an idea of what hip status is like when breeders make the first cut for breeding decisions. But we recommend a follow-up PennHIP at 6 months to 1 year of age, or later. If the dog was in the 70th percentile at 16 weeks of age, the DI could change somewhat if repeated at an older age, since pups are still growing rapidly at that age. The most accurate PennHIP result, based on our studies, can be obtained at 1 year of age. For this reason, if it is only in your means for 1 PennHIP evaluation for the dog, it should be performed at 1 year of age.

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Q. Is a certain amount of flattening of the heads allowed or must they be perfectly rounded? Why do breeders hear of so many dogs with 'loose' hips at 1 year or under but by 2 they are fine? Some do not pass the OFA but when they re-xray at an older age they do?
A. PennHIP cannot speak for the OFA in regards to flattening of the femoral heads in their scoring system. In PennHIP, we only use the hip extended view to examine for the presence of osteoarthritis, which doesn't include a degree of femoral head flattening as a specific criteria. Most dogs normally have some degree of femoral head flattening because a ligament attaches at that site. Dogs with loose (hip dysplasia susceptible range of DI > 0.3) hips when evaluated with PennHIP at a younger age, such as 16 weeks, will stay loose. Even some dogs evaluated to be tight (DI < 0.3) at that age may become loose or stay tight, since the dog is still growing. It is for this reason we recommend a later PennHIP evaluation at age 1 year or older when a dog is evaluated at an earlier age. One of the many benefits PennHIP evaluation has over OFA is that it gives you a risk assessment of your dog's susceptibility to hip dysplasia that is useful and more predictive over time. OFA scoring only gives you an OA/subluxation read at one point in time, and according to our studies, is not accurate in predicting their susceptibility to developing hip dysplasia in the future. It also is a subjective score and not an objective measurement, which means that the same radiograph could be sent in multiple different times and may not always receive the same score. It is impossible for a dog to have loose hips at under 1 year of age and then suddenly be tight-hipped/normal later- this is physically impossible. What you are seeing is evidence of the subjectivity of the OFA scoring method. PennHIP is recommended to determine the dog's true laxity and eliminate the subjectiveness associated with the OFA grading scheme.

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