Tuesday, 1 September 2015

Our PennHIP Experience

Another rather long post that was quite difficult to write because of all the thoughts I have on this topic and how difficult it is to put them in a coherent order. Hopefully it makes sense.

Indi and I went to a vet in Bristol to have Indi's hips x-rayed. For reasons I am going to explain later in this post, I have become disillusioned with the BVA scoring system which is based on the extended view. Recently, vets in the UK have started to offer Penn hip scoring. Indi's brother went to the USA and was scored under this system with a good result, so I thought it was worth giving it a try.

You can click on any of the images in this article to see them in more detail.

For some further reading, most of the information this post is based on comes from the following three sources:
Here is the PennHip website. On the website are listed lots of published research papers about the method, showing it has been found to be reproducible and a reliable predictor of later DJD (degenerative joint disease). Evidence such as this I consider very important if I am going to subject my dogs to what is an expensive and in reality rather invasive test requiring anaesthesia and radiation.

Here is a paper with a detailed explanation of the BVA hip scoring method which is widely used in the UK and recommended by the Kennel Club.

Here is an excellent veterinary textbook with lots of information about hip dysplasia for those wanting to understand this condition better. If you are not familiar with the terminology, I would read the above paper about the BVA system first.

The vet we went to is Joe Fox at Highcroft in Bristol. If you are interested in finding a vet who can do the Penn method, you can find vets near to your postcode in the UK using the Penn website above. After I lost Pasha, I never want to leave a poodle at a vet or anywhere else unless it is absolutely necessary. I have tried using vets who sedate for BVA hip scoring before, and have not been happy with the results (more on this later) and because of this and my dislike for subjecting dogs to general anaesthesia for no good reason, I was actually considering ceasing doing any sort of radiographic hip evaluation on my breeding dogs at all. Fortunately, the staff at Highcroft were very reasonable and allowed me to book Indi in late morning, with the caveat that if there was an emergency, we might have to wait several hours. There wasn't an emergency, and so after Indi was assessed, a nurse administered an initial drug to prepare Indi for anaesthesia, and I stayed with her for 20 minutes in an empty consulting room until the drug had taken effect and she was drowsy. Then the nurse carried Indi in to the x-ray room and I waited outside while she was anaesthetised and it was carried out. The vet then showed me the radiographs, and as soon as Indi was raising her head I was allowed to collect her from the recovery room and put her in my van where she could come round properly in a familiar environment on the journey home.

We did this on a Friday, and on the next Friday we received Indi's results in an email from the vet, which I consider to be a good turnaround and much better than the equivalent BVA panel, which often takes a month. Indi's results are shown below:


Indi's hip laxity was measured in the 60th percentile for her breed, which means Indi's hips are tighter than 60% of Standard Poodles, which is a good result. The radiographs from which this result was calculated are shown below:


Penn Hip involves three different images, from top to bottom, the extended view (the same as for BVA scoring and other methods), the distraction view, and the compression view. The extended view is just to look at and assess if there is any sign of DJD, the distraction view is of the dog in a position that pushes the femoral heads out of the acetabula, and the compression view is a position that pushes the femoral heads into the acetabula. The compression view is used to assess the depth of the acetabulum and compared to the distraction view in order to calculate how much the femoral heads displace between the two different positions, to give an accurate measure of how 'loose' the hips are in terms of a distraction index (DI). The studies Penn have done on their method have shown that different breeds have different profiles, but as a general approximation over all breeds, DIs close to or under 0.3 have negligible risk of developing DJD, whereas DIs greater than 0.7 have a high risk of developing DJD.

If you look at the top image, you can see that the positioning isn't perfect. The image isn't symmetrical and Indi's left knee is leaning in towards her midline, which perhaps makes her left hip look slightly pushed out (the left hip is on the right of the image, so the picture is of Indi lying on her back with the 'camera' looking down). But this is nowhere near as important for the Penn method as it is for methods that depend on the extended position, so it doesn't matter, and the vet was quite honest when he assessed Indi and said she might be difficult to position well, because she is small and in muscular, lean condition, and the nurse commented when she listened to her heartbeat about how fit she was (when she finally kept still enough for it to be heard). Indi's pelvis is also not symmetrical and the vet said there was evidence on the radiograph that she had injured her right femur when she was very young, and compensating for this while she was growing has probably caused it, and the right hip is tilted towards the 'plate'. The right hip looks pushed into the acetabulum more than the left one. probably because of its position, and on a scoring system such as the BVA one, it would probably score better than the left one. Now, bearing in mind that Indi's left hip has a measured distraction index of 0.31, which is close to the ideal of 0.3, look at the lower images of distraction and compression of the left hip (on the right of the image). This gives you some idea of the normal, natural range of movement in a normal hip that Penn's studies have found to have low risk of developing DJD. Indi's right hip, which looks tighter on the extended view, scored 0.46, so it is WORSE than the left one, although it is still not at high risk for developing DJD and marginally better than average for the breed, which is 0.47. Penn have published one paper I'm aware of about DI in poodles, and the results indicate that the risk of DJD in dogs up to age 3 with DIs of up to 0.5 is still less than 10% compared to ~2% at 0.3, and does not really start to rise sharply until DI reaches 0.6. Obviously further breed-specific research will be beneficial.

Now, on to the part where I'm going to opine and moan about BVA scoring:

The extended view is a neutral position. It's not like the compression position, which pushes the femoral heads into the acetabulum, or the distraction position, which pushes them out. The image of Indi's left hip in the distraction position shows that in a hip with a DI close to 0.3 has a range of normal movement -- it's a joint on a living animal and not a piece of machinery, so of course it does. In the neutral extended view, when the dog is relaxed because of anaesthesia, this normal range of movement could be just about anywhere, and is very susceptible to imperfections in positioning. If Indi's hip looked like it did in the distraction position in an extended view and it was sent for BVA scoring, it would be marked up for subluxation, Norberg angle, and for failing to align to the cranial acetabular edge.

This is the first dog I had BVA hip scored:

This dog scored 2+2=4. Yes, this is my beloved Pasha, the best dog I've ever owned. According to the BVA (see paper at top) dogs with scores of 2 per hip or under have anatomically perfect hips. Pasha probably did, because the positioning on this is not very good at all, and her pelvis isn't even straight, and despite this her hips still look very tight. I had no idea how to recognise good positioning or good hips at the time this was done, and went to an overpriced local vet and didn't even insist on seeing the image before they sent it for scoring. The tragic irony is of course that Pasha died when she was the same age as her hip score, from GDV, so she never reaped the benefits of her anatomically perfect hips when DJD is something that generally develops in old age. Nobody knows at the moment if GDV has a genetic component to it, but there are certainly worse things that can happen than having slightly loose hips.

This radiograph is Loki's:

The positioning on this radiograph is pretty much perfect. It was done by a more reasonably priced local veterinary practice, by an Australian vet whom I spoke to beforehand and insisted on seeing the radiograph. Both this and Pasha's were done under general anaesthetic. Loki's hips are not as good as Pasha's, and he scored 3+4=7. He would probably have scored worse if he had not been positioned so well. There is a good layman article about positioning here and an anecdote from an owner with radiographic evidence.

The next dog I had x-rayed was Hobsey. I'm not going to derail this post with discussing it in detail, and there is more information on Hobsey's page on the website, but the positioning was so bad that the radiograph wasn't even fit to be scored, so she has ended up with a radiograph with some signs of mild subluxation in one hip which is probably due to poor positioning, no evidence of DJD, and no score. I looked into other vets who do sedation rather than GA and did not find very many. One of them was very proud of his positioning, and had every right to be from the images I saw, but the resolution of the images was poor, and on one image he said he wasn't able to tell if there was signs of early DJD. Obviously I am not going to send a radiograph where potentially the resolution is so bad it cannot be seen if there is DJD to a BVA panel and hope they give it the benefit of the doubt. The other vets I looked at all insisted on general anaesthetic, and this these reasons together were why I decided to try PennHIP instead of using BVA scoring on Indi.

The BVA system scores nine radiographic features:

The first two features (Norberg angle and subluxation) are to do with how loose the hips appear on the radiograph. The third (CrAE) is to do with both laxity and DJD. The remaining rows are all to do with DJD/osteoarthritis only. More information on them can be found in the BVA paper linked at the top.

Hip laxity is thought to be caused by a combination of environment while the puppy is growing and genetics. DJD is exclusively caused by environment -- it's the result of wear and tear on the hip joints. DJD is more likely to be seen in older dogs, mature dogs that do high-impact physical activities, and rarely in young dogs. My personal feeling is that it is unlikely that most poodles that have been reared in a suitable environment will show evidence of DJD on a radiograph at one year old, which is when BVA hip scoring is generally carried out. Interestingly, different breeds have different appearances of hip dysplasia -- apparently Bulldog breeds often have dislocated hips with no proper acetabulum at all, and GSDs tend to develop DJD even when their hips are not loose relatively speaking. Optimistic estimates of heritability of results from extended-view hip evaluations tend to be about 0.4, meaning that at least 60% of the observed result is down to environmental factors. The Penn method which assesses laxity only, describes a much higher heritability, although this varies between dog breeds and is still less than 1, indicating environment does play a part. While the radiographic features in BVA scoring are academically interesting to study, my feeling is that BVA scoring can only really group dogs into four groups:

1. Dogs with scores of 2 per hip or less -- described as being pretty much anatomically perfect in the BVA paper. My suspicion is that dogs who score this well do have a genetic advantage that influences their hip conformation. In many breeds, the proportion of these dogs is very small. Off the top of my head, I can think of only 4 poodles alive whose scores I have seen which are this low, and two of them are first and second degree relatives of Pasha. Penn's research would seem to agree with this small a proportion, as Indi's brother's DI is 0.34 on both hips and he is in the 90th percentile for the breed.

2. Dogs with scores over 4 and into the teens, without any scores below the 3rd row, which have varying degrees of laxity which are highly influenced by positioning.

3. Dogs with hips so lax they are dislocated or almost so in the extended position. The worst score a dog can achieve under the BVA scheme representing completely dislocated hips but no DJD is, per hip, 6 for Norberg angle, 6 for subluxation, and about 3 for cranial acetabular edge, giving a total of 15+15=30. Hips that are normal should not fully luxate even when they are placed in the distraction position, so if the subluxation on an extended position is more than would be reasonably expected under distraction, this confirms abnormal looseness.

4. Dogs that already have DJD. In older dogs, this is probably less significant than in young dogs. Some conditions such as injuries, infections, or cancer in the bones, can cause an appearance resembling DJD. That the DJD is there is probably of more relevance than how advanced it is.

Because a lot of the BVA system is about measuring DJD rather than laxity, and because dogs to be used for breeding are generally scored before DJD is likely to develop, and because the appearance of laxity in the extended position is so susceptible to positioning, I feel that this system is less relevant to breeding dogs than schemes like PennHIP where the focus is in acquiring a measure of laxity accurately. PennHIP does cost more than BVA -- it was £400.15 for Indi whereas BVA scoring usually costs half that or slightly more. I feel if I am going to spend money on a radiographic hip evaluation, it is better spent on something that provides meaningful information, rather than on doing a test as a platitude because it's cheap and recommended.

The recommendations of a lot of hip evaluation schemes suggest only those dogs better than the breed median be bred, and those that are worse be discarded from breeding. This, they claim, is selection pressure that will reduce the incidence of hip dysplasia. I find it hard to put into words how damaging to genetic diversity it is to throw away half the gene pool of the breed on every generation. It would not be so bad if the test could be carried out on puppies when the selection of which dog to keep for breeding takes place, but it cannot be done until the dog is a year old. The current median BVA score for standard poodles, according to the BVA's information as of 2014, is 10. This means the BVA recommends that only poodles with single-figure scores are bred, and the others should not be bred. In practice, poodles with hip scores under 10 are bred, and generally so are poodles with scores of under 20. Poodles with scores of 20 or more are either not bred from, or bred from anyway, often with the radiograph not submitted for scoring if it looked really bad. No real selection occurs, and the reduction in scores the BVA seems to be so proud of is quite possibly more likely to do with people being more aware of the importance of good positioning and proper rearing environment, and hips that are radiographically obviously poor not being submitted for scoring.

The 'better than average' idea is also absurd when one considers a hypothetical breed that has generally very good hips. If the average DI for a breed is 0.2 and PennHIP says that dogs with DIs 0.3 or under have negligible risk of DJD, not breeding a dog because it scores 0.21, or even 0.3 and in the 10th percentile for that breed, is utterly idiotic. Similarly if a breed has a very poor score on average, if the average DI for a breed is 0.8 and a dog scores 0.79, this dog and its progeny's risk of DJD is really no improvement.

This also means that breeders who want to appear respectable and not be ostracised breed their litter, choose their breeding prospect as a puppy, wait until the dog is a year old, and if the score isn't good enough they have to start all over again after investing time and love and hope into the puppy they chose. This ISN'T selection. Quite possibly if all the other pups in the litter went as pets, the breeder is now in the position of having bred a litter that contributed nothing back to the breed. Breeders need to be able to preserve their breed. They can't do that to their full potential if half the dogs they have are pets that are never bred from, taking up space that could be given to dogs that can make a genetic contribution to the future. We do tests like eye certificates and SA biopsies because there are serious diseases that occasionally occur in the breed, and we want to keep those occurrences occasional. This is a somewhat crude method and a genetic test would be better and would mean we could eliminate these diseases, but it's all we have for now. Having half the dogs in the breed have a 'disease' which often has no symptoms (DJD as a result of hip dysplasia often does not manifest until old age, and many dogs whose radiographs show evidence of osteoarthritis don't have symptoms) is not an acceptable situation.

To be quite honest, I would not have been deterred from keeping Indi as a potential breeding dog even if her DI had put her in the 40th percentile. Unless there was evidence of DJD or her hips near dislocated when she was put in the distraction position, there is not a serious problem provided she remains healthy and her other test results are OK. The reason as I see it for breeding a breed is that you preserve it, hopefully improve it slightly, and don't contribute to the problem. That means that when I die or can't breed dogs any more, what I leave behind won't be afflicted with inbreeding depression, outbreeding depression, popular sire syndrome, or rampant genetic disease, and it will retain as much of the genetic diversity as possible that it started with, and be an improvement on what I started with. Improving on what you start with means just that, using tools available to you to make each generation an improvement on the last. It doesn't mean you draw a line in the sand and throw away everything on the wrong side of it.

Something interesting about PennHIP is that it can be used on puppies as young as 16 weeks and apparently can accurately assess their hip laxity. Therefore, there is a better method for those looking to improve their dogs' hips that involves gentle selection pressure and should over time improve results:

If you already have your breeding prospect, have it scored under whatever system you like. Unless the radiograph indicates there is a serious problem, or the dog develops other problems, don't discard the dog as a breeding prospect. How you interpret the dog's result is going to depend on the specifics of your breed, and it is helpful to look at research published on your breed by PennHip or other as to what level of laxity starts to present a problem, and if hip dysplasia is a serious problem in your breed or bloodline, and it has a large gene pool without other serious problems in it, you can probably afford to be more selective. If the result is not as good as you would like, try to find a mate with a much better result if possible for your dog. When puppies are born, select your favourite puppies according to whatever criteria you like -- conformation, temperament, etc. Narrow your choice down to the two best pups, and keep them until 16 weeks and have them PennHIP scored. Choose the puppy with the lowest DI, and sell the other puppy to whatever sort of owner you think is suitable, which should not be as difficult as selling a 1-year old since the puppy is still young and you have probably put some work into training it.

If you do this for a few generations, your average DIs should improve. This is a method which is much better for maintaining genetic diversity than just getting rid of the genetics of dogs just because they score worse than an arbitrary cutoff point.

For some breeds, the KC is now publishing estimated breeding values based on BVA hip scores. My feeling is that these are at best just something amusing to look at, and at worst something that can be abused. BVA hip scores are at least 60% the result of environmental influences, and studies have suggested that the biggest influence occurs in the first two months of life while the puppy is with the breeder. Naturally puppies born to the same dam and reared in the same environment are going to score similarly. Naturally, looking at the progeny results of stud dogs who have been used widely on many different bitches in 'myKC' reveals results that are all over the place. Breeders who rear dogs in the best possible environment tend to be careful where their puppies go, and if a novice buys a bitch puppy from such a breeder, they tend to get the breeder as a mentor with the puppy, so looking at good scores in dog families may be more the study of the transmission of memes between breeders rather than genes between dogs! It is extremely unfortunate that some try to use hip scores from the dogs of other breeders as ammunition, and discrimination against bloodlines because of hip scores and favouring of ones that produce low scores (where there may be other problems not as high profile as hip scores) in mating decisions, even if there is a substantial genetic component, is a quick fix that sacrifices diversity for the sake of fast results.

Finally, to further emphasise the importance of environment on orthopaedic conditions like hip dysplasia, below is a table comparing different environmental factors that have been found to influence hip dysplasia and how the best and worst breeders are likely to approach them. It is true that breeders with an ethos best represented by the right column are more likely to use some sort of radiographic hip evaluation to inform their breeding decisions, but they also bring up the pups in an environment that gives the pups the best possible start. If you are considering buying a puppy as a pet, this is something to keep in mind.

Puppy Farm Careful Breeder
Example
Flooring
Cold, cramped, dirty concrete pen in an outbuilding
Warm, hygienic non-slip surface inside house
Dam
Unloved, not a family member
Can be fed anything and amounts and composition may be inappropriate for pregnancy/lactation
Loved and cared for
fed quality appropriate food throughout pregnancy and rearing
Exercise
Crowded in pen, bouncing up and down on hard floor, no opportunity for pups to 'stretch their legs'
No toys
Climbing on and interacting with suitable toys and objects
Allowed to exercise on grass at own pace in appropriate weather
Diet
May be poor quality, unbalanced, or inappropriate
High quality, balanced, suitable for life stage
Quantity
Food left out constantly or thrown on the floor or in a communal dish, allowing greedy puppies to eat too much
Once weaned, pups are fed from individual bowls to ensure each eats the optimum amount
Table comparing breeder environments that have opposite effects on orthopaedic conditions

This dog was raised in the environment described on the right.

In fact, he is the offspring of Loki and Pasha, whose radiographs and their scores are shown in this post. He scored 2+2=4 like his mother. Perhaps genetics do have something to do with this, but certainly environment plays a major part. His parents were both brought up in environments much closer to the one on the right than the one on the left, and his parents both have scores better than the breed median, as does one grandmother, but one grandfather's score is at the breed median, the other is 5 points higher than it, and the other grandmother was never hip scored. Had they not been bred because of their scores or lack of, this dog with an excellent score would never have been born.

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