|
|
THE PennHIP PROCEDURE
In 1937 veterinarian
Gerry Schnelle wrote a paper entitled Bilateral Congenital
Subluxation of the Coxofemoral Joints of a Dog. It was a landmark
original description of what we today call Canine Hip Dysplasia. CHD
for short, there are very few topics among dog owners, breeders, and
veterinarians that can rival the spectrum of emotions evoked by this
abnormality of the dog’s coxofemoral (hip) joint. The PennHIP
procedure is a useful tool in determining the degree of hip joint
laxity in dogs.
WHAT IS HIP
DYSPLASIA
In short canine hip dysplasia (CHD) is a developmental abnormality of
the hip joint. CHD is the most common orthopedic disease is dogs and is
a polygenic (influenced by a number of genes) inherited trait. The
radiographic changes observed with CHD include luxation or subluxation
of the hip and osteoarthritis (degenerative joint disease). It is
generally accepted and now scientifically proven that hip joint laxity
(hip looseness) plays a major role in the development of osteoarthritis. Because
osteoarthritis commonly causes pain and
discomfort in the affected joints, the dog with CHD often has impaired
mobility and a diminished quality of life. 
Therefore, any method that objectively measures hip joint laxity may be
helpful in evaluating a dog’s risk for developing osteoarthritis and CHD.
This information would assist the dog owner or breeder in deciding which
animals not to breed as well as in selecting the best individual
animals for breeding. Before we go
further in this discussion of PennHIP, there are a few terms that are
important to know. Take a look at the
Definitions
below and refer to them if you get confused.
CHD in many respects
has been ignored by some, underestimated by a few and fervently analyzed
by many. The evidence collected over the past 65 years since Dr.
Schnelle first brought it to our attention has demonstrated that the
presence of hip dysplasia in a dog has definite genetic determiners.
More recently, data has been presented that shows the development of
joint deterioration in a dog with CHD correlates well with the degree of
joint laxity present in the dog. If hip laxity is present, other
environmental factors, such as
nutritional, can influence the degree of expression of abnormal signs
associated with Canine Hip Dysplasia. The determination of the degree
of CHD in a dog, the ultimate debilitative effects of any hip joint
abnormality, the heritability factors for the potential offspring and
the ethics of breeding a dog with CHD all factor into making this topic
somewhat complicated… as the scientists say “It’s a multi-factorial
subject”. Fortunately, however, the determination of degree of joint
laxity using PennHIP Distraction Index is not subjective, but an
accurate quantitative measurement.
TRADITIONAL
EVALUATION
The ventrodorsal (front to back), hip-extended (legs pulled straight
rearward) radiographic view as approved by the American
Veterinary Medical Association in 1966 has been a standard for
positioning of the dog on the x-ray table. The radiograph needs to be
taken with the dog under sedation or anesthesia for proper and
consistent positioning. If the positioning is not correct, the
asymmetrical images of the hip joints will make accurate interpretation
nearly impossible. This traditional and still widely accepted method of
evaluating hip structure is used by many hip screening programs
throughout the world, including Orthopedic Foundation for Animal (OFA),
the Institute for Genetic Disease Control in Animals (GDC) and PennHIP.
The OFA system and registry has been one strategy attempting to improve
the knowledge base and selection process for breeders interested in
eliminating CHD from a breed. Many breeders and veterinarians agree that
the incidence of CHD has noticeably decreased over the years since it
was first described, partly because awareness of CHD among pet owners
and breeders has reached fairly high levels. For years the OFA protocol
has been the most commonly utilized method of screening and certifying
dogs as having normal or dysplastic hips. Unfortunately, subjective
variables can enter into the OFA evaluation process. Although
preliminary radiographs can be revealing, a potential drawback with the
OFA protocol is the fact that for certification and definitive
evaluation a dog must be 24 months of age or older at the time the hip
radiographs are taken. Additionally, occasional criticism is heard that
some veterinarians unknowingly affect the evaluation of the radiograph
by their subjective positioning of the dog at the time the radiographs
are taken; plus individual interpretation of what is visible on the
radiograph is sometimes challenged. There exists the disappointing fact
that outright fraud has occurred by unscrupulous individuals who
misrepresent a radiograph as being of an animal other than the one
actually radiographed.
PennHIP:
(University of Pennsylvania Hip Improvement Program)
And that is precisely where the PennHIP topic becomes important.
Commercially available since 1993, this procedure has been and was
developed as an objective method of evaluating dogs’ hip structure. It
evolved as a direct result of the subjectivity factors and age
constraint (maturity) limitations inherent to evaluation and
certification of dogs by the OFA and other screening programs. PennHIP
research published in peer reviewed journals has shown that different
breeds have different susceptibility to osteoarthritis. Therefore, in
PennHIP evaluations each breed is compared to its own.
PennHIP incorporates
an improved method for evaluating the integrity of the canine hip. It
has great potential to lower the frequency of CHD when used as a
breeding selection criterion. The technique assesses the quality of the
canine hip and quantitatively measures canine hip joint laxity.
Originally developed in 1983 by Gail Smith, VMD, PhD and his colleagues
at the University of Pennsylvania, School of Veterinary Medicine, the
procedure was conceived and developed as a new scientific method for an
earlier and more accurate diagnosis of CHD. Years of research conducted
in Smith’s laboratory proved the diagnostic method to be capable of
estimating the risk (susceptibility) for CHD in dogs as young as sixteen
weeks of age.
|
It is
especially important to perform a Distraction Index (DI) on
dogs that have normal appearing hips on the ventrodorsal
extended view, such as appears to be the case in the image
on the right. Dogs that are diagnosed as having
excellent hips on the traditional VD view can actually have
a huge amount of laxity. PennHIP's recommendation is to
limit breeding to those dogs that have normal appearing
hips on the VD hip extended view and that also have a DI at
the breed's mean laxity or tighter. |
 |
The PennHIP method
is a novel way to assess, measure and interpret hip joint laxity and hip
conformation. Three separate radiographs are taken of a sedated or
anesthetized dog…
* the distraction view
* the compression view
* the standard ventrodorsal, hip-extended view.
The distraction view and compression view are used to obtain accurate
and precise numerical measurements of joint laxity and conformation. The
hip-extended view is used to diagnose osteoarthritis using criteria
similar to the OFA and other hip screening organizations. Precise
positioning of the dog by trained certified PennHIP members is
imperative and any radiographs that do not conform to prescribed
positioning are rejected and must be repeated.
Interestingly, a
dog's hip laxity at 16 weeks of age will be much the same at one year,
two years and older. For most breeds, the PennHIP evaluation can be
done as early as four months of age. Recommendations based upon peer
reviewed and published research, though, state that the reliability of
the PennHIP method slightly improves with age, with one year being
marginally superior to six months, which in turn is marginally better
than four months. The Distraction Index (DI), obtained via the
distraction view radiograph, is not subjective. It is an accurate
numerical measurement that has been shown to be reliable.
DISTRACTION INDEX
Also called the DI, the Distraction Index is obtained with the aid
of a fulcrum so that a radiograph can be taken with the head of the
femur as far out of the hip socket as possible. This distance is then
measured. Hips with DIs on the distraction view that are close to 0 are
considered to be tight, while DIs close to 1 are considered to be very
loose. The DI is an indication of the "percent out of joint" that the
femoral head is displaced from the acetabulum (socket). For example,
DI=0.58 means the femoral head comes out of the joint by 58%, DI=0.75,
75% out of joint and so on. The Distraction Index of PennHIP is
not subjective, but an accurate quantitative measurement that has been
shown to be repeatable and reliable. A dog with a DI approaching 1 has
a very high degree of predictability for developing Canine Hip Dysplasia
and subsequent osteoarthritis... and should not be considered for
breeding purposes.
WHO DOES PennHIP
PROCEDURES
Only certified individuals who have undergone special training and have
successfully demonstrated their expertise in the technique are permitted
to perform PennHIP procedures. Since both PennHIP and OFA use the
ventrodorsal, hip-extended view, your
PennHIP certified veterinarian can make a copy of the hip-extended
radiograph for submission to the OFA at the time your dog has the
PennHIP procedure. You do not have to abandon OFA opinion nor schedule a
separate appointment for an additional radiograph.
As of November 2001,
there were 1,076 certified PennHIP members. 977 members are in the
United States and Canada and 99 in 19 other countries. Darryl N. Biery,
DVM, Professor of Radiology and a Board Certified Veterinary Radiologist
at the School of Veterinary Medicine, University of Pennsylvania states,
“All PennHIP certified veterinarians have passed a certification process
that includes course work and quality control supervision.”
With the devastating
effects of CHD, the PennHIP procedure is a welcomed addition to the
opportunities dog breeders have in selecting only the best individuals
for carrying on the ideal traits of each breed. That selection
flexibility is enhanced by the opportunity to go beyond the qualitative
description of calling a hip joint “normal” by actually applying a
numerical value to “normal” and abnormal joints. That numerical value
is called the Distraction Index (DI). With PennHIP the breeder can make
a more appropriate choice among breeding individuals with “normal hips”
by referring to the Distraction Index and selecting the best individuals
in the “normal” group… the ones with the tightest hips.
The PennHIP
Laboratory publishes its findings in scientific journals. Published
information is disseminated to all PennHIP members; it is also shared
with interested breed clubs and routinely appears in publications within
the dog fancy. Will the PennHIP protocol replace the traditional OFA
protocol? Only time will tell. But this newer method of evaluating
dogs’ hip joints will be one more tool to improve future generations of
dogs. So for all of us who love and respect canines, the PennHIP
procedure should be a welcomed addition to our diagnostic and predictive
treasure chest.
ADVANTAGES OF
PennHIP
There are a number of advantages associated with doing the PennHIP
procedure rather than the traditional method of radiography:
The PennHIP Procedure is...
* A scientifically validated method.
* Performed on dogs as young as 16 weeks of age.
* 2.5 –11 times more hip laxity is measured compared to the conventional
ventrodorsal, hip-extended radiographic evaluation method. This
objective measurement of hip joint laxity is critical since the amount
of laxity detected has a direct relationship to the likelihood that a
dog will develop arthritis (the looser the hip the greater the risk).
* PennHIP radiographic score has a higher heritability coefficient, and
therefore has a greater potential to improve hips through selective
breeding than the ventrodorsal, hip-extended view alone.
* Requires mandatory submission of hip films to minimize bias in
database. (Even hips showing obvious dysplasia are sent in and added to
the database.)
PennHIP OR OFA?
What procedure should a dog owner select when attempting to gain
valid information about a dog’s hip status? I posed this question:
“What is the major difference between having a dog evaluated by the
OFA as opposed to having a PennHIP
evaluation done?” In response Dr. Smith states, “The PennHIP
radiographic evaluation has been shown scientifically to give a truer
estimate of hip quality; it is more accurate, more reliable and as
mentioned it can be performed as early as 16 weeks of age. The major
advantage of the PennHIP method is its unique ability to identify
true-normal dogs, dogs not susceptible to hip dysplasia.”
Small animal
practitioner Mara DiGrazia, DVM, of New Hyde Park, N.Y., although not
PennHIP certified, states her approach to the question of which
procedure to use: “If a client has a young puppy that they are
considering to use for breeding I would recommend the PennHIP
radiographs rather than waiting for an OFA. This is because PennHIP can
predict as early as 4 months of age what degree of hip dysplasia the dog
may develop. Early OFA radiographs may not reveal the same degree of
laxity in the joint. Early identification of hip deformity can make a
world of difference to the dog’s future life. The PennHIP procedure can
bring about a timely spay or neuter if the dog has been found to be
unworthy of breeding due to poor hip conformation. The dog’s lifestyle
can then conform to its needs as a pet rather than as a working or
breeding dog.“
Definition
of terms:
Articular
Cartilage, nourished by synovial fluid, is the cartilaginous
surface of the end of a bone, which contributes to the function of a
joint.
Osteoarthritis,
Degenerative Joint Disease (DJD) is marked by degeneration or
breakdown of the articular cartilage, hypertrophy of bone at the margins
of the joint, and changes in the synovial membrane and joint capsule,
and is accompanied by pain and stiffness.
Joint Laxity
refers to the amount of looseness in a joint. Generally the more laxity
the greater the potential for DJD from the trauma associated with
loosely fitting joint members.
Luxation
means dislocation. A luxated hip is one that has extreme laxity such
that it displays dislocation of the two bones of the joint. The x-ray
image at the top right of this page demonstrates a fully luxated hip on
the right side of the image.
Subluxation
means a partial dislocation of two joint
members. The x-ray image at the top right of this page demonstrates a
subluxated hip on the left side of the image.
The ventrodorsal,
hip-extended radiographic view: This refers to the standard
positioning of the dog on its back on the X-ray table. The radiograph
is made with the beam projection from the front to the back of the dog
while the rear legs are pulled symmetrically rearward. To be done
properly, the view is generally done under sedation or anesthesia.
OFA Update:
The Issue of
Joint Laxity
and Stress
Radiography
By
G.G. Keller,
D.V.M., MS,
Diplomate of
A.V.C.R.,
Executive
Director
Orthopedic
Foundation
for Animals,
Inc. and E.A.
Corley,
D.V.M.,
Ph.D.,
Diplomate of
A.V.C.R.
OFA does
not
normally
respond
to the
various
opinions
expressed
by
individuals
on
Internet
web
sites
and/or
chat
lines.
Instead
OFA
maintains
a web
site
(http://www.offa.org)
to
provide
information
that may
be of
value to
breeders
and
veterinarians.
However,
a
response
to the
opinions
expressed
by many
people
is
prompted,
as the
opinions
appear
to have
deteriorated
to the
point of
becoming
non-productive.
OFA
stated
its
position
on any
testing
method,
including
PennHIP,
that
involved
stress
radiography
to the
breed
clubs in
1994.
This
posting
is a
review
of that
position.
Contrary
to some
Internet
postings,
OFA, a
not-for-profit
organization,
does
support
and
encourage
research
on joint
laxity
and its
meaning.
The fact
that
joint
laxity
plays a
role,
but is
not the
only
factor
to be
considered
in
development
of hip
dysplasia
and its
secondary
changes
of
degenerative
joint
disease,
has been
recognized
for over
30
years.
This
fact is
not in
dispute.
T he
issue
has
been,
and
remains
to be,
the
relationship
of
laxity
that is
demonstrated
by
forcing
the
heads of
the
femurs
away
from the
acetabula
by
palpation
or a
fulcrum/stress
device
(i.e., a
distraction
device)
to
abnormal
laxity
(functional
laxity
that
occurs
in hip
dysplasia.)
Since
1972,
when an
independent
panel of
scientists
classified
the
techniques
for
demonstration
of joint
laxity
by use
of an
externally
applied
force as
experimental,
OFA has
financially
supported
three
research
projects,
recommended
by
external
review,
to
answer
the
basic
question.
Dr.
Belkoff,
et.al.
(VCOT 1:
31-36
1989)
developed
a device
that
measured
the
amount
of force
applied
to the
hips and
noted
that
some
dogs
that
demonstrated
abnormal
amounts
of
laxity
were
free of
hip
dysplasia
at
necropsy.
These
authors
questioned
the
meaning
of joint
laxity
as
demonstrated
by
force.
The
other
two
projects
supported
by OFA
are
ongoing.
PennHIP
is
another
technique
for
demonstration
of
forced
(passive)
laxity
that is
also
attempting
to
answer
the
basic
question
of the
relationship
of
passive
laxity
to
functional
laxity.
OFA
encourages
their
research
efforts;
however,
OFA
takes
exception
to the
marketing
techniques
and
claims
used to
promote
the
PennHIP
testing
method
for
clinical
use, as
the use
of this
method
appears
to be
premature.
In other
words,
commercialization
(marketing)
of the
method
has
outreached
the
science.
OFA
feels
that
general
use of
PennHIP
as a
mass
screening
test
method
for hip
dysplasia
is
prematur
e
because:
- The
primary
basis
for
marketing
PennHIP
was
reported
by Dr.
Smith,
et.al.
(Am J
Vet Res,
July
1993)
using a
modification
of a
previously
described
positioning,
stress/fulcrum
technique.
The
study
was a
survey
type
involving
142 dogs
(105 of
which
were
German
Shepherd
Dogs).
The
results
of the
study
were
questioned
by Dr.
Susan
Shott of
the
Biostatistical
Unit,
Rusk
Cancer
Institute
(Am J
Vet Res,
December
1993)
who
challenged
the
analysis
of the
data and
stated:
"The
data
does not
support
the
author’s
conclusion
that the
DI was
the most
important
and
reliable
phenotypic
factor
for
determining
susceptibility
of hips
to
degenerative
joint
disease
... and
that
this
determination
could be
made
with an
acceptable
degree
of
accuracy
as early
as 4
months
of age."
- Dr.
Lust,
et.al.
(Dr.
Smith
was a
coauthor)
in a
report
involving
42
Labrador
Retrievers
(Am J
Vet Res,
December
1993)
concluded
that a
DI of
<0.4 at
4 months
of age
correctly
predicted
normal
hips in
88% of
the
cases
and a DI
of >0.4
correctly
predicted
hip
dysplasia
in 57%
of the
cases.
The
authors
further
concluded
that:
"Distraction
indices
between
0.4 and
0.7 and
at
either 4
or 8
months
of age
were not
associated
strongly
enough
with
evidence
of
disease
to be
clinically
reliable
in
predicting,
on an
individual
basis,
the
outcome
for
dysplastic
hip
conformation
when the
dogs
were
older."
- No
breeding
data
based on
PennHIP
h as
been
reported.
Dr. E.A.
Leighton
(JAVMA,
May 13,
1997)
reported
on
genetic
progress
in
improving
the hip
quality
in
German
Shepherd
Dogs and
Labrador
Retrievers
in the
Seeing
Eye
closed
colony
of dogs.
In less
than 5
generations
the
percentage
of hip
dysplasia
was
decreased
from 55
to 24%
in the
German
Shepherd
Dogs and
from 30
to 10%
in the
Labrador
Retrievers
using
the hip
extended
position
and a
modified
OFA
evaluation
procedure.
PennHIP
DI
measurements
were
also
made but
the mean
DI
across
generations
did not
change.
It
should
be
pointed
out that
DI was
considered
experimental
and
breeding
selection
criteria
did not
include
the DI.
It will
be
interesting
to see
the
results
when DI
is
included
as a
selection
criterion.
With the
above
reservations,
plus
experience
with the
issue of
joint
laxity,
OFA
would be
remiss
in its
responsibility
to
either
endorse
or
reject
the
PennHIP
testing
method.
In other
words,
the jury
is still
out!
This
leaves
the
breeder
in a
dilemma
as to
which
testing
method
to use,
OFA or
PennHIP
or both,
as they
are
entirely
different
test
methods
for the
same
disease.
There is
a great
economic
advantage
to
breeders
for
determination
of the
hip
status
at a
young
age and
to
assess
the risk
for
development
of hip
dysplasia
at a
later
age. OFA
reported
(Vet
Clinics
of No
Am, May
1992) on
a study
of 3,369
dogs
from 25
breeds.
Reliability
of the
preliminary
evaluations
ranged
from
71.4% in
the
Chesapeake
Bay
Retriever
to 100%
in the
Welsh=2
0Springer
Spaniel.
The
preliminary
evaluation
appeared
to be
breed
dependent
and
dependent
on the
evaluator’s
experience
with the
skeletal
development
of that
breed at
the age
of
evaluation.
When
faced
with the
problem
of
comparing
entirely
different
test
methods
for
determining
dysplasia,
scientists
evaluate
the
results
of
reported
values
for
false
negative
(probability
of
diagnosing
a
dysplastic
dog as
normal),
false
positive
(probability
of
diagnosing
a normal
dog as
dysplastic),
specificity
(probability
of a
normal
dog
receiving
a normal
evaluation),
and
sensitivity
(probability
of a
dysplastic
dog
receiving
a
dysplastic
evaluation).
These
values
for OFA
preliminary
evaluations
by age
and hip
ratings,
in a
different
population
of dogs
than
previously
reported
(Vet
Clinics
of No
Am., May
1992)
have
been
reported
(JAVMA,
November
1,
1997).
The
false
negative
and
false
positive
values
for
PennHIP
were
reported
by Dr.
Smith
et.al.
(Am J
Vet Res,
July
1993).
No
report
of
selectivity
or
sensitivity
values
for
PennHIP
were
given.
There
were
2,332
dogs in
this OFA
study
and 142
dogs in
the
PennHIP
study.
The
limited
number
of dogs
resulted
in a
larger
confidence
interval
for the
PennHIP
values.
Confidence
intervals
(CI) are
determined
so that
one can
be 95%
confident
that the
true
value
lies
within
the
calculated
range.
The
false
negative
values
for OFA
evaluations
were
8.9%
(CI=5.9
to
12.9%)
at 3-6
months,
6.0%
(CI=4.4
to 8.0%)
at 7-12
months
and 3.8%
(CI=2.6
to 5.4%)
at 13-18
months
of age.
The
false ne
gative
values
for
PennHIP
evaluations
were 12%
(CI=1.5
to
38.3%)
at 4
months
and 0%
(CI=0.0
to
15.4%)
at 12
months
of age.
It
appears
that the
probability
of
retaining
a
dysplastic
dog in
the
breeding
pool is
the same
for
either
test
method.
However,
the
false
positive
values
for
PennHIP
were
significantly
greater
(48% at
4
months,
57% at 6
months
and 38%
at 12
months)
than
those
for OFA
evaluations
17.6% at
3-6
months
(CI 10.8
to
26.4%),
10.0% at
7-12
months
(CI 5.7
to
15.9%)
and 8.5%
at 13-18
months
(CI 4.8
to
13.6%).
It
appears
that the
probability
for
removing
a normal
dog from
the
breeding
pool is
less
with the
OFA
evaluations.
Dr.
Adams,
et.al.
(JAAHA,
1998,
34:
339-47)
reported
(using
palpation,
OFA
method,
PennHIP,
and
Norberg
angle
measurements)
on
results
of a
study of
hip
laxity,
in 32
dogs
from 4
breeds
(12
Greyhounds,
4
Labrador
Retrievers,
12 Irish
Setters,
and 4
hound-mix)
at 6-10
weeks
and 16
to 18
weeks
that
were
compared
to
detection
of
degenerative
joint
disease
at 52
weeks of
age.
Five
hips
with
evidence
of
subluxation
but no
evidence
of
degenerative
joint
disease
on the
OFA type
evaluation
of the
hip
extended
view
were
eliminated
from
analysis.
The
authors
concluded
that DI
and
Norberg
Angle
measurements
at 6-10
and
16-18
weeks
were the
most
reliable
predictors
of hip
dysplasia,
at 52
weeks of
age,
with DI
being
more
reliable
than
Norberg.
The OFA
and
palpation
methods
at 6-10
or 16-18
weeks
were not
reliable
predictors.
This is
not s
urprising
as
reliability
of OFA
preliminary
evaluations
has been
shown to
increase
with age
of
evaluation.
The OFA
report
(JAVMA,
Nov.
1997)
included
380 dogs
evaluated
at 3 to
6 months
of age.
The
reliability
was
89.6%
(CI=85.4
to
92.9%)
for
normal
evaluations
and
80.4%
(CI=71.4
to
87.6%)
for
dysplastic
evaluations.
The mean
age was
4.8
months
(19.2
weeks)
and the
median
age was
5 months
(20
weeks)
which
means
that
over
half of
the dogs
in the
OFA
study
were
older
than in
the
study
reported
by Dr.
Adams.
OFA data
and
PennHIP
data are
not
representative
of the
general
population
of dogs
because
the
programs
are
voluntary,
most
dogs are
in pet
homes
and are
not
radiographed,
and not
all
radiographs
of dogs
radiographed
are
submitted
for
evaluation
by
either
program.
For
example;
if an
attending
veterinarian
determines
a dog to
be
dysplastic,
by
either
method,
the
radiograph(s)
may not
be
submitted
to save
the
owner
money.
PennHIP
collaborators
may take
the hip
extended
view
first
and if
the
radiograph
shows
evidence
of
dysplasia
the DI
views
may not
be taken
or the
owner
may not
allow
submission
of an
obviously
large DI
measurement.
Breeders
are
aware of
the
economic
value of
early
screening
of dogs
for
determination
of the
hip
status.
They
should
also be
aware
that
both OFA
and
PennHIP
use the
radiographic
evaluation
of the
same hip
extended
projection
as the
standard
for
comparing
with the
results
of the
early
evaluations.
The OFA
standard
represents
the
consensus
of203
independent
evaluations
at >24
months
of age
by board
certified
veterinary
radiologists.
It is
not
clear
who
evaluates
a
radiograph
submitted
for
PennHIP
determination,
but the
original
study
reported
the
standard
to be
Dr.
Smith’s
evaluation.
This
evaluation
at >24
months
of age
has
approximately
5% false
negative
finding
as
reported
by Dr.
Jessen
(Proceedings
of a
1972
symposium
on hip
dysplasia)
and by
an
internal
OFA
study of
dogs
evaluated
at 24
months
that
were
re-evaluated
at an
older
age.
This is
why OFA
requires
the 24
month
certification
age.
Voluntary
submissions
to
PennHIP
will
provide
information
on the
range,
mean and
median
of the
DI
measurements
for the
various
breeds.
The
meaning
of the
measurements
remains
unclear
and will
require
repeat
studies,
on the
same
dogs, at
>24
months
of age.
Breeders
must be
aware of
the
cost,
strengths,
and
weaknesses
of the
test
methods
available
for
evaluation
of the
hip
status
before
making
the
choice
of a
specific
testing
method.
Once the
choice
is made,
it must
be
followed
for
generations
before
progress
in
improving
the hip
status
can be
evaluated.
OFA data
has
demonstrated
marked
improvement
of the
hip
status
in the
Portuguese
Water
Dog (AKC
Gazette,
Nov
1991)
and the
Chinese
Shar Pei
(Barker,
Mar/Apr
1995).
OFA data
on all
breeds
was
independently
evaluated
and
reported
by Dr.
Kaneene
(JAVMA,
Dec
1997) an
epidemiologists
from the
Population
Medicine
Center
at
Michigan
State
University.
The
study
compared
OFA
evaluatio
ns on
dogs
born
between
1972 and
1980
with
dogs
born
between
1989 and
1992.
The
population
consisted
of
270,978
dogs.
The
authors,
having
acknowledged
the fact
that
submissions
are
voluntary
and that
there is
bias due
to prior
screening,
concluded:
We
do
not
believe
that
this
is
the
most
likely
explanation,
because
the
increase
in
the
percentage
of
dogs
classified
as
having
excellent
hip
joint
phenotype
(+36%
[7.82
vs
10.64%])
was
substantially
larger
than
the
decrease
in
the
percentage
of
dogs
classified
as
having
canine
hip
dysplasia
(-21.%
[17.39
vs
13.82%]).
If
better
screening
of
radiographs
prior
to
submission
to
the
OFA
was
the
cause
of
the
increase
in
percentage
of
dogs
classified
as
having
an
excellent
hip
joint
phenotype,
then
because
it
is
easier
to
differentiate
dysplastic
hips
from
hips
with
normal
phenotypes
than
it
is
to
differentiate
hips
with
excellent,
good
and
fair
phenotypes,
we
would
have
expected
that
the
decrease
in
percentage
of
dogs
classified
as
having
canine
hip
dysplasia
would
have
been
larger
than
the
increase
in
percentage
of
dogs
classified
as
having
an
excellent
hip
joint
phenotype.
Unfortunately,
PennHIP
has not
been
available
long
enough
to
accumulate
the data
necessary
to
evaluate
the
effect
of this
test
method
over
time.
G.G.
Keller,
D.V.M.,
MS,
Diplomate
of
A.V.C.R.,
is the
Executive
Director
of
Orthopedic
Foundation
for
Animals,
Inc.
Dr.
Keller
received
his
Doctorate
in
Veterinary
Medicine
in 1973
an d was
in a
small
animal
private
practice
until
1987 at
which
time he
accepted
the
Associate
Director
position
for the
Orthopedic
Foundation
for
Animals.
He
received
the
Masters
degree
in
Veterinary
Medicine
and
Surgery
in 1990
and
Diplomate
status
in the
American
College
of
Veterinary
Radiology
in 1994.
He
assumed
the role
of
Executive
Director
for the
Orthopedic
Foundation
for
Animals
in
January,
1997.
Original
article
text
copyright
1998 by
Orthopedic
Foundation
for
Animals.
This
article
may be
reprinted
in paper
form for
educational
purposes
only,
with the
OFA
copyright
notice
intact.
This
article
is a
special
feature
of and
was
first
published
on
Workingdogs.com.
If you
wish to
link to
this
article
from
your web
site,
please
contact
the
Working
Dogs
Cyberzine
Publisher
for
linking
permissions.
Permission
is
not
granted
to copy
the code
or
design
from
this
page to
any
other.
Copyright
1998-2005
Working
Dogs;
all
rights
reserved.
|
|
|
Penn
Hip vs OFA
by Gordon Theilen, DVM
There has been good
discussion about value of Penn Hip and
that of OFA. I would like to emphasize a
few important aspects for all to
remember in their breeding programs.
Some of the following has already been
said and given here as important points
to remember.
1) Penn Hip measures hip
laxity not dysplasia which also is
called arthritis. Young dogs are
radiographed under sedation and pressure
is applied to attempt to move the head
of the femur out of the pelvic joint
socket that is held in place by the
central round ligament. Then radiographs
taken are sent to University of
Pennsylvania, College of Veterinary
Medicine and radiologists there rate the
hips ( Penn Hips) using a distraction
index formula and determine the quotient
up to 1. The ratings very for each breed
and usually a 0.4 or higher rating is
undesirable. Dogs with a high fraction
will be AFFECTED DOGS and show lameness.
I have forgotten the desirable fraction
for the Brittany, but it is around 0.4
or lower. The Penn Hip procedure does
not harm the pup. If there is a hip
joint laxity of 0.4 or more it was
genetic and not caused by the procedure.
Gene markers have been found for hip
laxity in some breeds and the left hip
joint has a higher percentage of
frequency than the right hip. Laxity is
under genetic control and not the same
as canine hip dsyplasia ( CHD). Some
dogs with CHD occur concurrently with
those that have hip laxity, but the two
are genetically separate entities.
2) Canine hip dsyplasia
are bone changes that start from
embryonic life ( under genetic control)
and may not be detected for years, but
up to 95% are detected by 2 years of
age, the time that Orthopedic Foundation
for Animals ( OFA ) certifies hips and
elbows with radiographs. Most dysplastic
hips can be detected by 6 to 8 months of
age, upwards of 85 to 90% occur by that
age. Thus, it is recommended to have hip
preliminaries done early about 6 months
of age and before 2 years of age. A
dysplastic pup at 6 months will never
have good hips at a later age. Another
value of OFA is knowing families being
free or at very low frequency for CHD
for up to 3 generations including not
only sire/dam, grandsire/grandam, and
great grandsire/great granddam but also
related relatives, sibs, cousins, aunts,
uncles etc. This helps establish
frequency of CARRIER DOGS. It is
generally obvious which dogs are
dysplastic, however, CARRIER DOGS are
normal and may be categorized as
excellent, good or fair. Excellent does
not necessarily mean there is less
chance for being a CARRIER, it only
means that dog has excellent hips, not
genetically free of CARRYING CHD.
3) Dogs that are Pen Hip
with a low distraction index and OFA
normal can still be CARRIERS. Dogs with
normal hips can still be CARRIER DOGS.
The condition that so many neglect to
know about or recognize. CARRIERS are
the key to riding unwanted genes from
the population. The only real way to
effectively do this is by open registry
and or OPENNESS by all breeders.
Brittany owners and breeders should
consider as a breed club becoming
members of Canine Health Information
Center ( CHIC). The mission: to provide
a source of health information for
owners, breeders, and scientists, which
will assist in breeding healthy dogs.
CHIC is an organization that works
together with OFA and AKC Canine Health
Foundation. As of September 2004 over 30
parent breed clubs had become members of
CHIC. You can find out more about CHIC
by seeing
or .
4) To find CARRIER DOGS
one can do this by carefully keeping
records and being aware of the health
and or unhealthy condition of offspring
from dogs you wish to purchase a pup or
breed for a litter. Fortunately we now
have at our disposal modern technology
as well to combine with the art of
breeding.
5) DNA profile of your
dog and family of dogs can help find
CARRIER DOGS. UCD, School of Veterinary
Medicine, Division of Canine Genetics
will send DNA swabs free of charge to
any Brittany owner desiring to have
their dogs entered into the Brittany DNA
Bank. It will take thousands of samples
to have an effective DNA Bank. Many
persons across the Nation are now
collecting and aiding Scientists at UCD
develop this Bank. Laboratory personal
are desirous of ABC becoming members of
CHIC and together we hopefully will find
CARRIER DOGS for not only hips and
elbows but for a myriad of other health
and trait problems. It also will be a
repository for documenting and
maintaining wanted health and traits.
Contact kathryn Robertson < krrobertson@ucdavis.edu>
for swabs. For serious questions on
genetics contact Mark Neff PhD < mwneff@ucdavis.edu>,
in charge of Brittany DNA Studies or for
lesser technical questions contact me.
Please let me know as chairman of the
Health Aspects and Genetic Defects
Committee of ABC whether we should
pursue membership as a parent club in
CHIC.
6) CARRIER DOGS can not
easily be found using DNA unless there
are thousands of samples at the
scientist disposal.
7) MAINTAINING
GENETICALLY STRONG DOGS can not easily
be documented without thousands of DNA
samples.
We as a breed are
extremely fortunate to have the Brittany
DNA Bank established at UCD, few breeds
have such an opportunity. This was all
made possible by the Marvin D. Nelson
Jr. Memorial Fund established in 2004 by
ABC. Of the $30,000 so far donated, none
of the monies have been spent, all have
been banked until the Fund substantially
grows hopefully to 1/2 to one million
dollars. Thus, donations are always
needed, so we as Brittany owners can say
we have contributed directly to finding
genetic make up for maintaining
genetically strong breeding stock or for
finding CARRIER DOGS for unwanted health
problem or traits and develop breeding
strategies to handle the unwanted. This
type of research is very expensive and
we must develop more ways to help pay
for needed research. For donations see
Trust this helps all appreciate what
CARRIER DOGS are all about and why they
are the nemesis in all good breeding
programs to maintain and better the
breed.
|
