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 The PennHIP Radiograph

 Rationale, Technique, Differences, and Value

by Fred Lanting


As the author of "Canine Hip Dysplasia", and an international lecturer on orthopedic disorders, as well as a dog show judge, I am frequently asked to comment on similarities and differences in the procedures used and information obtained when radiographs are taken for OFA and other leg-extended positions as compared to the PennHIP evaluation, which you will see is an improved diagnostic technique.

The Methods

By now, you know that the acronym stands for (University of) Pennsylvania Hip Improvement Program. This program arose from scientific inquiry, which in turn had its roots in the two related parents of invention: need and curiosity. The need was the desire of breeders and buyers for an earlier idea of how good were the hips of their canine "products". For several years in the beginning of OFA, breeders who got into the program in earnest made some progress, and many were able to avoid high incidence of severe HD in their lines. But a plateau was reached before total satisfaction could be attained, and they started to look for a means to progress beyond where they were, especially regarding early identification of the most likely carriers of the most "bad genes". Curiosity is the very heart of science, the "need to know"; in this case the question was "What must we learn to do in order to provide that early information in a valid and reliable manner?" The 30-plus years' history of the older hip dysplasia control programs had not resulted in satisfactory progress, so by the early 1990s researchers at that veterinary college in Philadelphia developed equipment and techniques to satisfy both breeder and scientist needs. Times change: what was acceptable in the past is not enough now; the bar has been raised, and to perform today we must jump higher, do better. The Orthopedic Foundation for Animals was established in the mid 1960s to collect radiographic data on hip dysplasia (abnormal hip joint development) and to register and publicize those dogs with more normal joint appearance so breeders could avoid the worst ones, which also might be the worst "carriers". The American Veterinary Medical Association (AVMA) developed guidelines for positioning the dog for its radiograph in order to show the maximum number and extent of bony growths and remodeling of bone contours. In doing so, vets discovered an important principal: there was a correlation between those abnormalities and laxity (loose fit). Both for the individual's risk of affliction and the risk of bestowing the causative genes upon future descendants, the phrase "Tighter Is Better" became an obvious truth. The AVMA position, adopted by OFA and foreign breed clubs, is that of a dog lying on its back in a similar way that we bipedal humans stretch out in our beds or coffins. It is certainly not a "natural" position for a quadripedal animal - one that travels on all four limbs of approximately equal lengths. In order to make a dog assume this supine humanoid position, the legs must be pulled (extended) with some force and restraint, or the dog would pull the knees up (flex them

forward toward the chest and head). Conversely, the "neutral/natural"

position for the standing or moving dog is with the vertical femurs

(nearly 90 degrees from horizontal) making an angle with the pelvis of

somewhere near 120 degrees. For Homo sapiens it is the erect position

when standing or moving. Neutral means that position in which there is

the greatest state of relaxation in the muscles used to extend or flex

the limb. Not only are the muscles and ligaments most relaxed, but also

the joints are then the loosest they will ever be. When the quadripedal

dog or bipedal man is standing at ease, a very few nerve impulses are

all that are needed to maintain balance by triggering a very few muscle

fibers on all sides of the joint. The contractions in the rear parts of

our legs keep us from falling forward, for example, while at the same

time the momentary contraction of a few "front" muscle fibers counteract

their effect.

It is very important to understand this stasis or

position of most neutrality, this balance of forces, in order to

understand one of the significant differences in AVMA's current protocol

and the position used by PennHIP. The AVMA-OFA position stretches

(tightens) the muscles on the belly side and front of thigh while not

letting those on the back side operate in contraction and balance.

Using this view with legs extended unnaturally, we "wind up" the

muscles, tendons, and ligaments in and around the hip joint and tighten

the joint capsule. The soft tissues closest to the joint are primarily

the white-tissue, high-collagen types such as tendons and ligaments, and

these do not extend (change length) to the degree that muscle fiber can.

Thus, the twisting of white-tissue fibers is like twisting a nylon rope

with two sticks turning in opposite directions, but in this case it

tends to cause bones to be pushed closer together - the femoral head

deeper into the socket than it would otherwise be. This artificially

tighter-than-natural aspect contributes to the high false-negative rates

in the OFA-certified dogs, as pertaining to laxity. Remember, both

degenerative joint disease (DJD) and joint space are grounds for

diagnosing HD in this method. Penn makes a semantic distinction between

DJD as the definition of HD, and laxity as being a risk factor for

eventual DJD.

While the hip-extended position is best for discovering DJD, it is not

best for uncovering latent laxity, or what I call "covert laxity".

False-negative means that a passing grade is given because the true

laxity was not observed, and that is the biggest drawback of the

hip-extended methods worldwide. There are some individuals (usually of

certain giant mastiff-family breeds) that do not develop DJD but are

OFA-assessed as dysplastic because of laxity at two years' age. But even

more importantly, there are a greater number of dogs of other breeds

that are adjudged "normal" at one or two years but later develop DJD or

produce an unacceptably high percentage of dysplastic descendants. Thus,

the accuracy of the hip-extended methods is gravely flawed. The gene

pool is hurt most by these false negative diagnoses.


Latest Improvements

Two movements in America arose in the past decade or two

that promise better progress than does adherence to OFA numbers as the

way to coxofemoral nirvana. One is the proposal to use a voluntary

"open registry", promulgated by the Institute for Genetic Disease

Control (GDC). The other is PennHIP (University of Pennsylvania

Veterinary School Hip Improvement Program). I had the pleasure of

working with the OFA's first "program director", Penn's Dr. Wayne Riser,

when I was researching and preparing my book, Canine Hip Dysplasia, and

I also have had the good fortune to visit Dr. Gail Smith (PennHIP) in

Philadelphia in the late 1980s. I reviewed his methods, philosophy, and

results, and am increasingly a supporter of this protocol. At present,

only PennHIP has the accuracy, repeatability, precision, and scientific

foundation for real and rapid progress in producing better hips. The

Seeing Eye, Inc. has turned to the distraction index (PennHIP) as a

means of assessing hip quality.

You can learn more about the procedure if you are on Internet, by

"tuning in" to <>,

<>, and


In the PennHIP technique, the dog is placed in a

position that is even more neutral than standing naturally because the

small effect of gravity is diminished. While under chemical relaxants

sufficient to prevent resistance to manipulation, the dog's femurs are

spread apart (distracted) with the force applied as close to the hip

joints as possible. One of three radiographic exposures is made at that

time, and the actual displacement is measured. An index is calculated in

order to take into account the various sizes of dogs and their femoral

heads/acetabulums. Any dog with an index of lower than 0.3 is

practically guaranteed to never get HD. So far there have only been a

few "semi-exceptions" in the many thousands of dogs evaluated. PennHIP

does not make breeding recommendations, only evaluations; it leaves the

decisions up to you, and counseling up to your veterinarian and peers.

It should not be surprising to anyone that the looser the hips, the less

accurate a prediction of a specific grade or severity might be,

especially in the hip-extended method. HD is developmental (DJD might

not show up right away), progressive (it'll eventually be worse), and

multifactorial (environment has a part to play in the expression of the

bad genes). Some young dogs will get worse than others even with the

same DI.


Other Differences

Other differences exist. There are three radiographs

used in the PennHIP procedure, and only PennHIP-certified vets may

submit them. Every dog's films enter the database, so there is not the

skew or bias as found with the OFA-type registries. The "first" film

(actually, it doesn't much matter in which order they are made) is

identical to that used by the older method: the traditional extended-leg

picture for the study of bone abnormalities - in some cases, especially

the worst ones, laxity is also apparent here. The second film is of the

knees-up neutral position with a very small compressive force pushing

the femoral heads into the sockets. While not as important as the other

two, this view allows an evaluation of congruity, how neatly the round

head fits into the curve of the socket. It is the third view that really

makes all the difference. While the dog is deeply "under", the patented

distractor unit is placed between the legs at the groin, roughly

parallel to the pelvis. Twin bars in this device that is shaped like the

Roman numeral II act as the fulcrum, and when the lower legs are held

near the hocks and pressed together, the vet leverages the femoral heads

away from each other and outward (laterally) from the sockets. No covert

laxity escapes this view.

The films are sent to the PennHIP Analysis Center, where a handful of

people evaluate them (OFA uses a panel of radiologists that rotates or

varies constantly). DJD presence or absence is noted on the first film,

and circle gauges are laid on the third radiograph for use in

objectively measuring the displacement. It is here where the paths

diverge markedly: OFA, AVMA, SV, and most foreign hip registries or

breed clubs use only the subjective hip-extended view, while PennHIP

adds the objective view. At Penn, the results are added to those already

in the database and compared. A report is issued that gives the

Distraction Index, which can be thought of as expressing the percentage

that the head is out of the socket. Another part states where this

particular dog stands in relation to the average (mean) for its breed,

expressed as "percentile". For example, if the mean DI for GSDs is 0.41,

your Shepherd with a DI of 0.53 will be in a percentile between 50 and

zero (worse than half of the breed). A percentile of 80 means that your

dog has tighter (better) hips than about 80% of those in the breed. The

mean can vary a little with time, especially when there is a low initial

number of dogs in the database. However, there is no escaping the facts

that "tighter is better" and that a relative threshold of safety of 0.3


PennHIP-certified vets have to pass a training and

subsequent testing regimen. For OFA, any local practitioner may submit

films, even if all she or he has ever X-rayed for in the past has been

fractures. Some clubs, such as the SV (GSD club in Germany) have a list

of approved vets who may submit films.

PennHIP researchers and method do not show estrus to be

a factor in the distraction view. In fact, there appears to be no

veterinary literature yet, to support the idea that it is so, even in

the leg-extended view. Furthermore, a study performed at the veterinary

school at U of PA definitively showed that hip laxity, whether on the

distraction view or the hip extended view, was not affected by estrus.

Their conclusion is that that scientific evidence refutes the purported

relationship of estrus to hip laxity.



The great value of PennHIP is the higher accuracy and

reliability of evaluations done at an early age, so owners don't spend

more money than necessary in training for more demanding work, or even

breed a dog that has a relatively high risk of later transmitting many

bad genes to progeny, or itself developing DJD. The accuracy and

repeatability of DI is just about as valid at six months age as

throughout life; in fact about 95% reliability is seen in pups even as

young as four months. The report by OFA that they too, now have equal

predictive value (JAVMA, 1997) was refuted by a University of Wisconsin

study published later and has not been confirmed by other independent

research. Similarly, the OFA claim of progress in the past

quarter-century has not been supported by data or experience elsewhere.

The claims in their news release were reduced to just a 2.83% increase

by the time the article was reviewed and then published in JAVMA in

1997; that would indicate that the inflated numbers in the OFA mailings

to clubs might not be all that impressive. All that our reliance on OFA

numbers has done is to allow very slow, perhaps almost imperceptible,

progress in some lines of some breeds and, in a statistically

insignificant amount, the "excellent" ratings in a few breeds. In almost

all others, more than thirty-five years of partial use of OFA for

breeding decisions has resulted in no progress, and in a few breeds the

situation may actually have worsened. Breeders complain of a plateau

reached in rates of progress when relying solely on OFA certification.

During the seminar on HD and other orthopedic disorders

that I have presented in many countries, I recommend a few points to

keep in mind when comparing the methods:

1. PennHIP is the hip-extended view plus two more radiographs that

show different things,

2. PennHIP has performed biomechanical studies on its radiographic

positioning while others have not,

3. PennHIP has performed much research in general and these have been

published in refereed journals to prove the science is valid. Those who

quote old information and say that "School is still out on the PennHIP

method" simply have been skipping classes in the past several years.

To replace the old combined-approach program of Bardens

palpation, wedge X-ray, and OFA-Good or Excellent, today I recommend

PennHIP's improved technology at 4-6 months (or any time before

breeding) as a viable and more accurate evaluation than all three of

those. For breeding, I advise my audiences to breed only to a partner

with higher than 50th percentile and lower DI than the mean, or a lower

DI than their own dog has; if they really want to accelerate progress,

to breed dogs with 0.3 or better. At least, get as close to that

threshold as possible, consistent with preservation of breed type and



What Does This Mean? The Situation Today: Slow Progress and Why

Why, after nearly some four decades of awareness, breeding changes, and

study, do we continue to hear from disgruntled or dissatisfied dog

buyers and breeders? Knowing that orthopedic disorders are almost all

genetic, one might think that it would be a simple answer to just breed

non-carriers of HD or ED (elbow disorders), or those with the best

genetic bank for good joints, but it is discovering these dogs that is

the challenge. Now that we have good diagnostic tools and effective hip

registries, the next step toward progress is for each breeder to develop

a breeding program. Fortunately, some breed clubs and other

organizations have already done the greater part of laying a foundation.

We have already potentially removed one of the two major obstacles to

progress, lack of understanding - or in other words, a lack of good

diagnostic guidance. After decades of using the hip-extended method,

most or all of those agencies have not generated a reliable heritability

figure for hip phenotype, nor has the method used in North America

reduced the incidence of HD as an average, across the breed populations.

Even when we look at subsets of canine populations in the serious

hobbyist world, whether we speak of individual or group (club) efforts,

we find that discontinued progress. One reason is the failure to adopt

the better diagnostic techniques.

The other reason for insufficient progress in reducing and ultimately

eliminating canine HD is non-compliance: the failure of most breeders to

stick with a really vigorous program of control and reduction. As you

might think, some breeders do their best to provide an environment that

causes the least dysplasia. However, genes that induce HD will thus be

masked and therefore retained in the stock. Few breeders are likely to

provide knowingly the adverse eugenics environment that would reveal

such genes. Part of that second reason (breeding practices) for slow

progress is the win-at-all-costs attitude maintained by many of the more

prolific breeders and leaders of breed clubs. In 1986 John Bardens, a

friend and a widely respected veterinary researcher, wrote to me, "Many

of the breeding [genetic] defects do not hit the breeder in the

pocketbook, and winning in the show ring is all that's important."

In some parts of the world, organizations and individuals have made

greater strides than those in North America have, but there is still a

way to go. The requirement in Germany for all radiographs to be recorded

and dogs' results made known, is admirable. The "sometime-pressure" in

the UK for vets to cooperate by sending in all films and getting the

results posted in the GSD database founded by Dr. Malcolm Willis has

helped a little. "Kiwis and Aussies" down-under use the UK system, but

also have room for improvement, as the following example would indicate:

I received a request for advice and counsel from a breeder in

Australasia who sold a pet-price bitch (no guarantees), paid for the

12-month radiograph, and got a BVA-type score of 11 in the Australian

hip scheme. When the bitch was approximately 3 years old, the buyers

decided they wanted to breed her, had her re-radiographed, and the score

was 81. Now, 11 is pretty good but 81 certainly is not. There are two

likely reasons for the two different readings, and I suspect both are

involved, even though the bitch had no clinical signs. One is the

inaccuracy of the supine, legs-extended procedure used in diagnosis in

the bulk of the world. The other is the rule rather than the exception

that loose hips at a young age (even if undetected) can be even looser

at an older age, when examined by the old method, and that DJD

(degenerative joint disease, arthritis, remodeling) is more likely then.

On the other hand, the experience with the great majority of cases

evaluated with the PennHIP method tells us that true laxity does not

change significantly after 4 months of age. At least, it is a rare

occurrence. If the prevailing culture and conventional wisdom amongst

breeders and vets in New Zealand and Australia ignores the newer,

improved, more accurate techniques, can they rightly blame the average

breeder? However, using a method shown to be not the best available

opens the door to litigation if defects should appear.


Progress in the United Kingdom

England, Scotland, Wales, and to a lesser extent countries with

historical ties to England, such as Ireland, Singapore, "OZ and NZ",

South Africa, and a few others have the potential for making great

strides in reducing HD. Part of the mechanism is in place; what breeders

need to do is use it. However, it may be difficult to accomplish without

government legislation or regulation by breed clubs and The Kennel Club.

They certify hips at one year of age; whether by government force or

voluntary peer pressure, I would like to see a reconfirmation of

phenotype normalcy after 2 years of age. Where the UK scheme continues

to fall short of being ideal, besides certifying at an early age, is in

not requiring all films to be submitted for the statistical study.

The BVA system concerns nine features; values of zero (no

irregularities) to 6 (horrible) are given to both left and right hips

joints, and the columns added. Most good breeders refuse to use any dog

with a grand total of anything more than 10. Dr. Malcolm Willis, for

many breeds, reports results with dogs' identities, in a form useful to

breeders. The British Veterinary Association's scheme was adopted or

copied in several countries historically connected to the old Empire.

Besides giving a quantitative score, the BVA/GSDL/KC scheme also has

another important advantage for breeders over the American OFA and some

other systems: it does produce information on progeny for several

breeds. Computer-retrievable data by kennel name, sex, birthdate, age at

time of radiography, and numerical value for each hip are used for

genetic analyses and for your own conclusions on with whom to breed

Schatzie, or whether to breed at all in deference to waiting to buy a

better dog. Say you like the looks of that dog that placed in the Top

Ten at his breed's national specialty show the past two or three years.

You look up his published hip scores, the mean score of his offspring

who are old enough to be assessed, and scan the column that tells you

whether and by how much he improved on the hip scores of bitches he

previously bred. If your breed club doesn't have that information, and

it's likely it doesn't, then it isn't doing all it can to serve you and

your breed. That's where "politics" can have a rare, beneficial effect

on purebred dogs and the sport. Get into or start a movement to require

your national club to hire a geneticist and give instructions to set up

a scheme similar to that now employed by BVA/KC. Yes, you can go it

alone, but your choices of breeding animals will be more limited than if

you were backed with the power of a club like the U.K.'s GSD League or

BAGS, or the GSD Council of Australia.

However, despite one of the most advanced information and control

schemes in the world, the mean scores for GSD males and females born in

the UK since 1959 have not changed a whit. About 45% of the UK's GSDs

have scores of 10 or below, with most considering the really "normal"

ones as being in the 0-5 range and the 6-10s being equivalent to what we

might call "near-normal". BVA scores as high as 20 could encompass the

level of quality in dogs given the 'A' stamp in Australia (not the same

meaning as the FCI's "A" designation for normal hips), but allowing that

many dogs to breed will slow the progress, regardless of breed or

country. Much better to make the requirements more strict each year

until something approaching the Swedish model can be had. Progeny data

are often seen in tables published in breed magazines. Obviously, those

sires that produce higher percentages in the 0-5 score category and (of

slightly lesser importance) a close second-high percentage in the 6-10

column, are the most desirable for improvement in hips and should be

preferentially bred to, as long as they also produce other important

good features.


Progress in Australasia

I was an honored guest and minor judging participant at Australia's

1991version of a "Sieger Show", the only foreigner to have been so

honored up to that date. It is called the "Main Breed Assessment" rather

than a "show", to avoid problems with the quasi-governmental Australian

National Kennel Council over practices allowed at regular shows, such as

pedigrees and catalogs in the judges' hands, gun sureness testing, and

especially information on what problems and good features the dog being

examined has passed on to its pups. I was very impressed that, in coming

to the placement decisions, the judges of the adult classes took into

account such things as the Australian 'A' stamp hip status (they

capitalize the letter there) of the individual as well as of siblings

and offspring, and other genetic factors as well as a full and expert

evaluation of the dog in question. The GSD people in Australia modified

the BVA scheme in conjunction with their own system. But I think they

give the 'A' stamp to too many animals for fast enough progress. The 6

grades are: N, NN, A, BL, III, and IV. Dogs are considered eligible for

the 'A' stamp if they have one of the four top grades of the six, and

this includes A (acceptable) and Borderline (many of which have what OFA

would call mild to moderate HD). As in Germany, this allows too many to

breed, and tends to act as a brake on progress. However, they have what

we in North America don't have, to any appreciable amount: progeny data.

This tends to offset part of the failings of less-strict radiograph

requirements, at least when comparing those schemes to OFA's. According

to an issue of the Australian GSD club's newsletter, almost all of the

Normals and 61.4% of the Near-Normals score 0-5. While GSD hip quality

has not increased as dramatically as quality of breed type, there are

hip requirements for breeding and, in time, increased strictures will

produce faster improvement. By limiting breedings to animals with the

'A' stamp, the Aussies and New Zealanders would exclude about a third of

the breed, better than what was done in England, but far inferior to

Sweden and what had been required in East Germany. Since 1981, the

percentage of Australian GSDs receiving the 'A' stamp has risen from 60%

to 80%, while grades III and IV (roughly equivalent to moderate and

severe HD in the United States or the BVA scores of 0-10) have declined

by half.


Japan and Pacific Rim

In the modern, dog-loving portion of Japan's society, progress in

control of hip dysplasia is just around the corner. I have judged and

lectured there, and long ago found great interest in improving many

areas. The Japan Kennel Club adopted PennHIP as the official and

preferred HD diagnostic procedure in the late 1990s. In Taiwan, dog

shows and interest in improved breeding, including for better hips, are

on the increase. When I lectured in Malaysia and the Philippines, I

found the progress and awareness at a lower level, but at least they

know enough to ask about hip status when they import dogs for their

breeding programs.


Comparing America to the World

In the Americas, the oldest hip registry is the OFA, but there are two

better ones in many respects: GDC (Institute for Genetic Disease

Control) and PennHIP. It's a good thing that OFA requires a minimum age

of 24 months for certification of "normalcy"; otherwise the situation in

most breeds in the USA would be dismally poorer. In most breeds it is

not that great, anyway, if you look at over-all breed statistics instead

of individual breeders' accomplishments. Paradoxically, the greatest

rates of progress are in some of those countries where dogs are

radiographed and certified for breeding as soon as they pass their first

year's birthdate, although they would be even better if approval were to

be delayed at least 6 more months. The reason, though, is that many

breed clubs outside America control authorization for breeding and

registering. In America, the AKC gleefully registers anything that comes

with money and the specified paperwork.

Compare progress in the U.S. with that in Germany, for example, and

specifically the most popular breed there and in the world, the German

Shepherd Dog. There has been a shift toward normalcy that came about in

spite of the practice of forbidding breeding rights only to those with

severe HD. As time went on, requirements for the VA (excellent-select)

class at the world Sieger Show in Germany were tightened more and more.

Not only must current highly placing show dogs have advanced training

degrees, they must also have the better hips and produce a good number

of normal hips as well as structurally desirable progeny. Today a dog

with a Noch Zugelassen (still permissible) rating might make it into the

VA class of some eight or ten dogs out of hundreds of competitors, but

he or she will not win the top title of Sieger or Siegerin, and there is

now pressure to keep the bad producers (with high ZW numbers) from being

honored with the Sieger title. There is annually increasing emphasis

that the very top be Normal, not just Fast (nearly) Normal. So the dogs

that get the most breedings in most of Europe will generally have the

best hips. There is no similar restriction in the sizeable Select class

for GSDs, neither at American (U.S.) national specialty shows, nor at

the smaller but similar Canadian Nationals. Nor is there anything

similar in the other AKC- or CKC-affiliated breed clubs. In America we

have neither the strict rules nor the peer pressure nor strong

suggestions to judges. We certainly aren't allowed to officially "know"

the hip status or other information important to the breed when we


Even faster progress could have been made by the SV if they would award

the "a" stamp only to dogs radiographed after 18 or 24 months of age.

And in other countries we could see an increase in the progress rates if

all dogs were to be radiographed and evaluated, even if they had poor

hips and would never be bred. It would give valuable data for progeny



Improve Your Breed by Improved Breeding

I recommend that breeders use this triad: evaluating

mature dogs for DJD, using PennHIP for early risk detection, and

following a Breed Value/Zuchtwert program. If, as is certainly

indicated, the DI gives a better picture of future hip quality in your

dog, then deductive reasoning would lead you to think of it as a

reasonably accurate indicator of the genotype of your dog. That means a

better idea of the proportion of bad hip genes to good hip genes, which

in turn means relatively how many bad genes are likely to be transmitted

to the next generation Now that, dear friends, is really revolutionary.

The lack of further progress we have seen in modern times, with ratings

by BVA, OFA, SV, ADRK, OVC, and other breed and veterinary organizations

is a direct result of their inability to indicate those hidden genes. A

dog that has a good picture in the extended-leg view yet still produces

an unacceptably high number of dysplastic offspring has too many of

those hidden genes. Since OFA would be the first to tell you of the link

between laxity and HD (remember, they actually use that as a

definition), the only reason for the poor progress is the covert laxity

I mentioned earlier. Therefore, using a logical process of thought, if

PennHIP shows more of this laxity than shows up in the AVMA-type view,

it better shows us the effects of more "hip genes". Since mapping the

dog's genome (at least finding markers for enough of the polygenic

perpetrators) is decades away, the DI evaluation as promoted by PennHIP

is by far the best tool in our tool chest.

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