THE PennHIP PROCEDURE
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
(hip) joint. The PennHIP procedure is a useful tool in
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
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)
a major role in the development of osteoarthritis.
causes pain and discomfort in the affected joints, the dog with CHD
has impaired mobility and a diminished quality of life.
any method that objectively measures hip joint laxity may be helpful in
a dog’s risk for developing osteoarthritis and CHD. This
would assist the dog owner or breeder in deciding which animals not to
as well as in selecting the best individual animals for breeding.
we go further in this discussion of PennHIP, there are a few terms that
important to know. Take a look at the Definitions below and refer
them if you get confused.
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
extreme laxity such that it displays dislocation of the two bones of
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.
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.
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
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
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.
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
laxity may be helpful in evaluating a dog’s risk for developing
and CHD. This information would assist the dog owner or breeder
deciding which animals not to breed as well as in selecting the best
animals for breeding.
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
|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 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.
hip-extended view is used to diagnose osteoarthritis using criteria
to the OFA and other hip screening organizations. Precise
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
evaluation can be done as early as four months of age.
based upon peer reviewed and published research, though, state that the
reliability of the PennHIP method slightly improves with age, with one
being marginally superior to six months, which in turn is marginally
than four months. The Distraction Index (DI), obtained via the
view radiograph, is not subjective. It is an accurate numerical
that has been shown to be reliable.
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
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
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
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
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
Distraction Index and selecting the best individuals in the “normal”
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
shared with interested breed clubs and routinely appears in
within the dog fancy. Will the PennHIP protocol replace the
OFA protocol? Only time will tell. But this newer method of
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
should be a welcomed addition to our diagnostic and predictive treasure
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...
1. A scientifically
2. Performed on dogs as
young as 16 weeks of age.
3. 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).
4. 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.
5. 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
procedure to use: “If a client has a young puppy that they are
to use for breeding I would recommend the PennHIP radiographs rather
waiting for an OFA. This is because PennHIP can predict as early
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.“