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Dealing
With Wrong Ideas about Hip Dysplasia |
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Background
Friends and fellow dog
fanciers: I was asked to comment on some accusations and remarks re HD that
have been on chat lists. First, so you understand where I am coming from, you
should know a little history of my involvement in dogs, veterinary science, and
hip dysplasia in particular. I got my first purebred
dog in 1937, bred my first litter in 1945, got my first GSD in 1947, started
handling and more extensive breeding in 1966, gave up all-breed pro handling to
become a judge in 1979, am one of only two in North & Central America
licensed by the SV (world parent club for the GSD), and I lecture and judge
around the world. I have done so in some 20 countries, lately several countries
per year. Among other books, I wrote “The Total GSD” and “Canine Hip Dysplasia”. I received early encouragement and support in
my research and study in orthopedic problems from the
founder of the OFA, Dr. Wayne Riser of the
Having constructed that
frame, I will now fill in more of the picture. Vet schools, breeders’
associations, and other groups across the globe do not invite me to speak and
judge without good reason. Nor do I write this from an antagonistic point of
view. It is strictly because of my dedication to the philosophical science of
logic and to the physical sciences that I feel compelled to rebut statements
that run contrary to those principles. I do so in a completely impartial
manner, and from the historical perspective mentioned above. Quotes from
Internet remarks by one Mr. D.N., for example, should not go uncorrected. I
have corresponded with him before and it is my impression that he does not read
the veterinary literature with comprehension, or he has some personal bone to
pick with Penn, or else he has some unreasonable attachment to or bias toward
OFA. I use his initial(s) instead of a name because his attitude and
misunderstanding are near-clones of those found in a few others. However, with
enough time, patience, and scientific evidence, most of such anti-progress naysayers are eventually converted by the facts and
deductive reasoning. I hate to mix personalities with science, but this
situation has been a source of irritation throughout the history of science,
and there is no avoiding
it.
Nature of HD
The facts about
HD, if they can be reduced to bare bones, are as follow: It is a developmental
and variably progressive disorder with incidence and severity that are related
to breed and body type as well as pain threshold. It is completely genetic in
origin (dogs do not get HD unless they have sufficient “bad genes”) but the expression
of those genes can be modified somewhat by environment, notably overnutrition but also exercise and weight. In the days
before X-radiography, when tending dogs (for example) worked hard for 18-20
hours a day, the worst carriers of HD in such working dogs were weeded out by
not breeding (or even allowing to live) those dogs that could not perform. As
sheep gave place to urbanization and modernization, there was less vocational
culling, and people needed an alternative means of detecting carriers.
Fortunately, the Curies had paved the way with X-rays; by the World-War-2 era,
diagnosis of canine and other animals’ degenerative joint diseases by casting
X-ray shadows onto photographic film became that means. Thanks largely to Dr.
Gerry Schnelle, it was also recognized in the 1920s and ‘30s that loose
ball-and-socket hip joints had much to do with pain and loss of usefulness. We
refer to that loose condition as laxity or subluxation.
Laxity had been palpated (felt) by a few methods of manipulating some
dogs’ joints and estimating the displacement of the ball (femoral head) from
the socket (acetabulum). We used the term subluxation more to describe what we saw on
radiographs, but the two terms have become nearly synonymous for most people.
The important
thing about hip-joint laxity that the people of Schnelle’s
day knew intuitively in the 1930s, the OFA proclaimed via deductive reasoning
since Riser’s work in the 1960s, and PennHIP has
scientifically, statistically proven since Smith & Biery’s
work began in the early 1980s, is that there is a definite correlation between
laxity and degenerative joint disease (DJD). This connection might be
relatively weak, as in Saint Bernard type bodies, or very strong as in gundogs
and herding breeds. Regardless of breed, however, PennHIP
has shown that as laxity increases, the relative risk of DJD also increases. The
slope of the curve or line on the X-Y graph may vary from breed to breed, but
the correlation is nevertheless real in all cases. The hip-extended
(leg-extended) position is ideal for viewing DJD, and has been the “backbone”
of the accepted radiographic diagnostic technique in every country since OFA in
Central
to this barrier against progress when relying only on the leg-extended view is
the fact that the position tends to unnaturally and artificially wind up and
tighten the soft tissues in the joint. The joint capsule is composed
primarily of ligaments, with muscles and tendons playing a supporting role.
Like a rubber band or a tourniquet that is twisted, these hip joint capsule
tissues tend to force the head of the femur more deeply and tightly into the acetabulum. Thus, in many dogs, we get a false sense of
security, a “false-negative” reading for HD’s laxity component. Since the
leg-extended registries such as SV, OFA, BVA, etc. have always used either
DJD or laxity to define HD, that means we erroneously
give a green light to the breeding of dogs with such false negatives. This
reintroduces an undesirable (and to many of us, an unacceptable) number of bad
genes into the gene pool. Obviously, good breeders want to eliminate or reduce
this pollution of the pool. Therefore, the need arose for a diagnostic
technique that would be more sensitive to true laxity than current methods
were. The technique developed at Penn in the 1980s was just such an answer to
that need, and this alternate route to the next plateau was as real as a new
and better approach to the summit is for a mountain climber. Using another
metaphor, it is like an improved sieve that traps pollutants and prevents them
from re-entering our potable water supply.
The (University of)
Pennsylvania Hip Improvement Program utilizes, in addition to the leg-extended
view for DJD, a neutral-natural position that closely duplicates the standing
position of the dog, but on its back. That position midway between the
most-forward and the most-rearward extremes of the dog’s stride,
is the one in which the joint capsule tissues are most relaxed, and therefore
laxity can be most accurately and easily manifested. PennHIP supplies a
mechanical device by which the veterinarian can distract (displace) the femoral
head, take a picture, and objectively compare that with the picture taken
before distraction. When I use the word “objective”, I refer to something that
we can measure --- a mathematical value.
Just as figures do not lie, laxity cannot hide from the distraction
view; you may get tired of me repeating that, but it should be drummed into our
heads. What looseness is there definitely will be demonstrated, and the
measurement will be repeated exactly or very closely. This is in contrast to
the leg-extended, twist-tightened, older method in which different evaluators
may come up with a range of laxity diagnoses days, hours, or even minutes
apart. Furthermore, there is far more subjectivity in the leg-extended
procedures. The only objective portion of that latter view is the use of the Norberg angle, which has been shown to have rather poor
predictive value for dysplasia’s DJD development.
Today and for the foreseeable future, the distractive view as expressed in
Penn’s “DI” (Distraction Index) is the most accurate, precise, objective
picture of current laxity, and the best indicator of relative risk, the best
predictor of probable eventual DJD. In my seminars, I make comparisons in much
greater detail than is feasible here.
Attacks from the misinformed
To return to the
aforementioned sniper attacks on the new knowledge of HD, an unpleasant task
but necessary response must be made. People who fall for DN’s
misinformed accusations do so mostly because they have not been clearly shown
the superior science of the newer technique, the understandable explanations of
the method. Very succinctly, he is completely wrong when he says (without the
backing of peer-reviewed, scientific data) that PennHIP
gives false positives for the presence of HD. The truth is that Penn’s
definition of HD is DJD; the OFA’s definition is either
DJD or laxity, or both. The truth is that laxity is always shown in the neutral
distraction view but it very often is undiscovered in the leg-extended view.
The truth is that Penn’s method is far more indicative of actual genotype
because of far better information re actual phenotype, and therefore that PennHIP is a much more advanced tool for the conscientious
breeder. The truth is that PennHIP gives us more
relevant and useful data, virtually no false positives, and almost zero false
negatives, which are the greatest hindrance to progress in genetic disease
reduction.
DN recalls “from
reading and discussions” many supposedly false positives in other techniques
(unproven and undocumented in the science literature) and illogically ties
these vapors to PennHIP. He
very erroneously claims that DI is the same as the “fulcrum” or “wedge X-ray”
of the 1970s, an untrue and misleading statement. Position alone
(neutral-natural or wound-up) is sufficient to blow that statement out of the
water. The misinterpretations continue; he says the force used to distract the
femoral head runs counter to the concept of diagnosis and creates the condition
of laxity. That is so transparently nonsense that it boggles the mind to
imagine anyone believing his statement. The whole idea of “raising the bar” for
diagnosis is to detect more covert HD than has been possible with the
leg-extended view! This head-in-the-sand approach coupled with that artificial
tightening of the hip joint capsule in order to take a picture conducive to
more false negatives should be obvious to any of our respective readers.
Distraction does not create laxity; it reveals it!
The
assertion that a strong vet would produce more distraction and displacement
than would someone with a light touch is understandable, but unfounded. Anyone with
knowledge of basic physics and anatomy knows that the relative inextensibility
of white connective tissue (ligaments) in the joint capsule is not at all
analogous to the coiled steel spring in a weighing scale. The latter will
produce a nearly perfect linear slope in a stress-strain graph, which means
that the pulling force applied is directly proportional to the displacement
(distance the weighted end of the spring moves). In any hip joint there is a certain
amount of looseness, and it takes but a very minimal distractive force (perhaps
a couple of
For this point,
Dr. Smith of Penn likes to use the “ball-on-a-rope” analogy. In the
hip-extended (OFA-type) position, the ball (femoral head) is hooked to a
spring; the harder you pull, the further the spring elongates, meaning that the
strength of the operator will have a marked effect on measured laxity. But in the neutral (knees up, flexed)
distraction position, the constraints of the hip act like the ball is hanging
vertically on a rope. You can pull the ball laterally with very little force
until the rope gets tight but after that point there will be no increase in hip
laxity, no matter how much additional force is added. They have never broken
the rope, by the way.
The “silence” DN
reports re his questions on what equipment is used to measure force is simply
because the
During the early and mid 1960s when I began my research in HD, I
was a weekend pro handler in the
I have had correspondence run-ins with Mr. N, and unfortunately
find him to be a sincere but closed-minded, somewhat illogical person with
opinions set in epoxy (a scientist always leaves the door open to possible
change based on evidence). People must eventually decide whom to trust, and
ride that particular horse across the river... changing in mid-stream or
choosing the wrong horse are equally disastrous. I was just reading the Bible
last night where it advises people not to hang between two decisions. I get
especially tired of trying to help people who allow themselves
to be blown in all directions by every changing wisp of wind. More frustrating than a
fickle friend and worse than a determined opponent.
From
Another Quarter: Faking?
The editor of a breed magazine for certain stock- and
companion-dogs wrote: “We were
discussing PennHIP on the Internet, and someone said
her vet talked them out of it. According to this vet, PennHIP
is notoriously easy to fake. By not exerting the right amount of pressure, the
x-raying vet can purposely cause a dysplastic dog to
get good results. According to the vet who made these claims, it's done all the
time, and consequently PennHIP results cannot be
trusted. (The person who posted this is a HUGE fan of OFA, mainly because of OFA's ‘gossip factor’, methinks. Club people like to print
OFA results in their newsletters, and resent PennHIP
not playing along with the game.) Your thoughts on the
subject, please?” Well, if I can
help anyone on the “Setter-L”, the English Shepherd list, or any other group, I
think the first response should be to refer you to a small collection of
some of my articles on a leading GSD website called "http://realgsd.net". But to answer this editor’s request, the
best thing to say to such a brainwashed (I almost typed "brainless")
vet is the old adage, "Put up or shut up". In other words, “Where's the proof?” This is
the most ridiculous thing I have ever seen in the way of opposition to PennHIP. It is similar to DN’s
charge, except that instead of supposedly damaging the joint (creating HD), it now supposedly hides it because of not enough
force! I have been through the training
sessions and I have first-hand knowledge of the force applied. I also have the scientific knowledge to
understand the difference between a linear stress-strain curve such as what you
get when you pull a coiled spring (for the greatest part of the force) and the
high-stiffness, nearly parabolic curve you get when you pull on a nearly
non-extensible material such as ligaments. That veterinarian is obviously not
acting in his clients' best interests, and he certainly is not being a credit
to the scientists he had as professors in college and vet school.
It is one thing to voice an opinion that
a procedure might be easy to fake (and I know that it's easier to put one over
on OFA than it is on PennHIP because "laxity
doesn't hide from the Distraction technique"); but it is downright
irresponsible and probably malicious to use a word like
"notoriously". You simply don't use "extreme" words when
disagreeing from a position of ignorance. Unless of course, you are following
the advice that I believe was attributed to one Adolph H. that if you tell a
lie that is big (preposterous) enough, often enough, and loudly enough, people
would believe it. That vet does not understand the procedure, and I'd bet cold
cash he has never seen a demonstration. If you do not exert enough distractive
force on the hips, one or more of three things are bound to happen:
- there will not be sufficient difference
in a relatively tight-hipped dog between the compressed and distracted
views, and P-H would tell him to do it over; or,
- the hips are going to be so loose that you can
see the laxity anyway.
- the radiolucent rods of the distractor
are covered with a tough Neoprene sponge rubber which must show on the
film that it has been squeezed enough; if it does not, the film would be
rejected.
There are only a very few who read and evaluate the films at Penn,
so there is not the reader-to-reader variance found in other registries that
use the hip-extended view. There are other incentives/penalties working to the
advantage of the breeder/owner: PennHIP vets would
lose their certification and therefore their prestige amongst other vets and
the breeder community if they played games like that described. Even
incompetence is not tolerated, if it ever appears... vets who don't do many P-H
films might "lose their touch" temporarily, but getting a film set
sent back and having to call the client in for a repeat because it wasn't done
properly, is a powerful motivator to get the job done right the first time.
Now, to be fair, we must realize that the
vet is being semi-quoted in a third-hand way, so unless one got this directly
from him/her, the malice or ignorance should be considered as having come
primarily from that "person who posted this". It is apparent that person did not do his
homework and investigate for himself the reliability of either PennHIP or the naysayer's
statements. To fail to check out both sides or sets of
arguments is irresponsible. If that person would keep his mouth closed and his
ears open for a couple of hours during my seminar (except to ask honest
questions) he would take another tack. I see it happen all the time. It isn't
because I'm so persuasive; it's because the science is so convincing. I present the Orthopedics
Disorders seminar all over the world, and would be happy to consider a date in
anybody's hometown if it fits my calendar. By the way, I’m not sure what the
writer meant by “resenting PennHIP for not playing
along with the game”, but it seems to hint at the pass/fail list that OFA
distributes, compared to the breed DI averages that PennHIP
publishes. Those clubs and magazines that print the OFA statistics, biased as
they are because not all films are sent in, can also get the PennHIP unbiased updates simply by asking for them. I don't
have Internet myself, but I'm sure they could get that info from
<www.synbiotics.com> and qualified breed club representatives (magazine
editors, health committee heads) could get on Penn's mailing list.
Estrus
Another magazine has asked me to
comment on the effect of estrus (heat cycle), and I
felt it would be a good idea to put that into this piece as a sort-of “p.s.” For many years
we breeders have been assuming that there were (regularly) differences in
observable hip joint laxity between films made in or near estrus
and those made in complete anestrus (not close to a
heat cycle). We also told each other that to get the best picture and the best
chances of “passing OFA”, we should take the pictures in the afternoon, after
the dog had been exercised and “toned up”, on a dog with good muscle
development from regular exercise over a longer period of time, not within a
couple weeks of estrus or several weeks of pregnancy,
and without sedation. This was based on intuitive supposition, and the OFA even
made statements to the effect that they were true concepts. There are two holes
in this otherwise neat scenario. One is that there has never been any
scientific study to prove the idea that joints are tighter or looser than at other
times. It simply “made sense” to many of us, because conventional wisdom shows
us that we are slightly longer when we wake up than after a day of gravity
compressing our spinal disks, and that hormones in late pregnancy cause a
woman’s pelvic symphyses to relax or bend so that
there is more room for the child exiting the birth canal. But does that
necessarily mean that the other joints are likewise affected, and that
ligaments somehow relax more than they would in other circumstances? No. It was
a faulty assumption, and there is no published study to support that. On the
other hand, a definitive study in Veterinary Comparative Orthopaedics and Traumatology (1997;10:69-74)
showed that hip laxity is NOT changed by estrus cycle
using either the OFA or the PennHIP
method. All of the OFA’s
contentions (and breeders’ assumptions about the effect of estrus)
are untrue, according to this journal report.
The other problem with that
reasoning is that we were basing our assumptions on the old and imprecise
leg-extended position. As I have mentioned, this natural position for humans
but unnatural position for quadrupeds tends to wind up and artificially tighten
the muscles, tendons, and ligaments in the area of the hip. We do not always
get repeatable results with that position. With the knees flexed and the distractor unit employed in the PennHIP
technique, however, the same amount of laxity is seen (with few and minor
exceptions) time after time. The dog’s full laxity is seen each time the dog is
radiographed in this position. There is no change in
DI attributable to a bitch being in heat or the other reasons, when this method
is used. In fact, researchers at Penn
have scientifically proved the point (see comment above) that it simply is not
true in the leg-extended view… although I have been saying that there are as
many examples that do not show this as those that seem to do so, Penn’s
study-based statement is that no examples
show significantly increased laxity with estrus.
So, the conclusion of the estrus-laxity question is (again) that true laxity does not
hide from the distraction procedure, that it very well might from the
leg-extended view, and that the role of hormones in canine hip joint laxity
(whatever it might be in other species and anatomical locations) is not
present, or it is immeasurable.
Recommended reading:
Some
Scientific Publications
(This is an abbreviated bibliography. For
more, see the Synbiotics or Pennhip websites.)
Puerto DA, Smith GK, Gregor TP, LaFond E, Conzemius MG, Cabell LW and McKelvie PJ. Relationships between results of the Ortolani method of hip joint palpation and distraction
index, Norberg angle, and hip score in dogs. J Am
Vet Med Assoc 1999;214:497-501.
Smith GK, LaFond E and Gregor TP.
Within-and between-examiner repeatability by experienced and inexperienced
examiners in performing distraction stress-radiography to quantitate
canine coxofemoral joint laxity. Am J Vet Res 1997;58:1076-1077.
Smith GK, LaFond E, Heyman SJ, Cofone MA and Gregor TP.
Biomechanical characterization of passive laxity of the canine coxofemoral joint. Am J Vet Res
1997;58:1078-1082.
Hassinger KA,
Smith GK, Conzemius HM, Hill CM and Gregor TP. Effect of estrus cycle
on coxofemoral joint laxity. Vet
Comp Ortho Traum 1997;
Smith GK. Advances in diagnosing canine hip dysplasia.
J Am Vet Med Assoc 1997;211:1451-1457.
Smith GK, Popovitch CA, and Gregor TP. Evaluation
of risk factors for degenerative joint disease associated with hip dysplasia in dogs. J Am Vet Med Assoc 1995;206:642-647.
Smith GK, Gregor TP, Rhodes WH and Biery
DN. Coxofemoral joint laxity from distraction
radiography and its contemporaneous and prospective correlation with laxity,
subjective score and evidence of degenerative joint disease from conventional
hip-extended radiography. Am J Vet Res 1993;54:1021-1042.
Submitted or in press
Fordyce
HH, Gregor TP, and Smith GK.
Correlation of OFA hip scoring to passive hip laxity derived from the
hip-extended and distraction radiographs. Submitted.
Vet Ortho Soc Ann Mtg, Val D'Isire,
France, 2000.
Smith
GK, Fordyce HH, Gregor TP, Puerto DA, Rhodes WH, Reid
CF, Bierry DN, LaFond E, Iriye A and Elliot E. Within
and between examiner agreement of subjective hip scoring from the ventrodorsal hip-extended radiograph in dogs. Submitted.
Leighton EA, Smith GK, Biery DN, Gregor TP, Stankovics M, and Holle D.
Heritability of the distraction index in German Shepherd
Dogs and
Abstracts
Fordyce HH, Smith GK, Gregor TP. Relative sensitivities of three methods to
measure passive hip laxity in the dog, in Proceedings. Vet Ortho Soc Ann
Mtg,
Puerto DA, Smith GK, Gregor TP, LaFond E, Conzemius MG, Cabell LM, and McKelvie PJ. The relationship of Ortolani palpation results and quantitative measurements of
passive hip laxity, in Proceedings. Vet Ortho Soc Mtg,
Smith GK, LaFond E and Gregor TP.
Within-and between-examiner repeatability by experienced and inexperienced
examiners in performing distraction stress-radiography to quantitate
canine coxofemoral joint laxity. J Am Vet Med
Assoc 1997;211:1260.
Smith GK, Hassinger KA, Conzemius MC,
Saunders HM, Hill CM, Gregor TP. Effect of estrus cycle on coxofemoral joint
laxity, in Proceedings. ACVS Scientific Mtg,
Smith GK, LaFond E, Heyman SJ, Cofone MA, Gregor TP.
Biomechanical basis for clinical repeatability of PennHIP
distraction radiography of the canine hip, in Proceedings. ACVS
Scientific Mtg,
Smith GK, Biery DN, Iriye A, Gregor TP, LaFond E. Frequency of
hip dysplasia in Golden Retrievers and Rottweilers and the effect of prescreening
of radiographs on reported CHD prevalence figures, in Proceedings. Vet
Ortho Soc, 1997; 61. -- also in Vet Comp Ortho Traum
1997;10,68.
Hassinger KA,
Smith GK, Conzemius MC, Saunders HM, Hill CM, Gregor TP. Effect of estrus cycle
on coxofemoral joint laxity, in Proceedings.
Vet Ortho Soc, 1997; 31.
-- also in Vet Comp Ortho Traum
1997;10:77.
LaFond E, Smith
GK, Gregor TP, McKelvie PJ,
Shofer FS. Synovial
fluid cavitation of the canine coxofemoral
joint: frequency, risk factros and effects in 6649
purebred dogs undergoing distraction radiography for hip evaluation, in Proceedings.
Vet Ortho Soc, 1997;40.
-- also in Vet Comp Ortho Traum
1997;10:80.
Smith GK, LaFond E, Heyman SJ, Cofone MA, Gregor TP.
Biomechanical characterization of passive laxity of the canine coxofemoral joint and its role in clinical repeatability of
laxity measurements, in Proceedings. Vet Ortho Soc, 1997;13.
-- also in Vet Comp Ortho Traum
1997;10:68.
Smith GK, Biery DN, Rhodes WH, Reid CF LaFond
E, Gregor TP, Waldman A, and Elliot E. Between- and
within- radiologist accuracy of subjective hip scoring of the VD hip-extended
radiograph, in Proceedings. Eur Assoc of Vet Diag Imaging Ann Mtg, 1996;2-3.
also,
in Proceedings. International Symposium on Hip Dysplasia
and Osteoarthritis in Dogs,
Smith GK, Biery DN, Rhodes WH, Reid CF, Gregor
TP, LaFond E, Waldman A, Elliot E. Between- and
within-radiologist accuracy of subjective hip scoring of the ventrodorsal hip-extended radiograph, in Proceedings.
International Symposium on Hip Dysplasia
and Osteoarthritis in Dogs,
Meinen J, Dueland RT, Adams WM, O'Brien R and Smith GK: Correlation
of early diagnosis of hip laxity by stress radiography, CT, OFA radiography, Norberg Angles and clinical palpations. A
preliminary report, in Proceedings. 20th Ann Vet Ortho Soc Mtg,
Smith GK, Gregor TP, Biery DN, Rhodes WH
and Reid CF: Hip Dysplasia Diagnosis: A comparison of diagnostic methods and diagnosticians, in Proceedings.
Symposium on Comparative Aspects on Hip and Knee Joint
Lesions in Dog and Man,
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Copyright 2001 Fred Lanting, Canine Consulting.
Mr.GSD@juno.com. All rights reserved. Please
view his site Real GSD.
NOTE: A well-respected AKC and Schaferhund
Verein judge, Mr. Lanting has
judged in more than a dozen countries, including the prestigious FCI Asian Show
hosted by Japan Kennel Club, the Scottish Kennel Club, a Greyhound specialty in