PennHIP - A New Scientific Method for
Early Screening of Canine Hip Dysplasia
Canine Hip Dysplasia (CHD) is the most common, heritable
orthopaedic problem seen in dogs. It affects virtually all breeds of dogs
but is especially problematic in large and giant breeds. Clinically, the
disease manifests itself in one of two ways:
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A severe form that typically afflicts the younger animal
and is usually characterized by marked pain and lameness, or:
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A more chronic form with more gradual onset of clinical signs
such as mild intermittent pain, stiffness and restricted range of motion in
the hips as the dog ages.
Breeders and Veterinarians have long sought a reliable
method to determine the likelihood of a dog developing CHD and passing that
genetic trait to any offspring. It was generally recognized that the
current diagnostic methods of hip evaluation were associated with
disappointing progress in reducing the frequency of CHD.
In 1983, Dr. Gail Smith a veterinary orthopaedic surgeon
and bioengineer from the University of Pennsylvania School of Veterinary Medicine, began to actively research and develop a new
scientific method for the early diagnosis of Canine Hip Dysplasia. Research
in his laboratory resulted in a diagnostic method capable of estimating the
susceptibility for CHD in populations of dogs as young as sixteen weeks.
The method has shown distinct advantages over the
standard Australian CHD diagnostic method that evaluates dogs at one year
or older. The University
of Pennsylvania Hip Improvement Program
(PennHIP) was founded as an extension of Dr. Smith's laboratory research.
Questions and
Answers about PennHIP
What exactly is
PennHIP?
PennHIP is a scientific method to evaluate a dog for its
susceptibility to develop Hip Dysplasia. The radiographic procedure
involves a special positioning of the dog so that the dog's "passive
hip laxity" can be accurately measured. In simple terms, passive hip
laxity refers to the degree of looseness of the hip ball in the hip socket
when the dog's muscles are completely relaxed.
Research has shown that the degree of passive hip laxity
is an important factor in determining susceptibility to develop
Degenerative Joint Disease (DJD) later in life. Radiographic evidence of
hip (DJD), also known as osteoarthritis, is the universally accepted
confirmation of CHD. Visit the PennHIP site by following this link. www.PennHIP.org
How was PennHIP
Developed?
The development of PennHIP has involved multiple
disciplines including biomechanics, orthopaedics, clinical medicine,
radiology, epidemiology and population genetics. The first phase of
development involved sophisticated biomechanical testing to determine the
optimal patient position for measuring hip laxity. By monitoring passive
hip laxity in dogs as they matured, it was discovered that hip laxity was
the primary factor in the development of the DJD characteristic of CHD.
That is, the radiographic expression of DJD was statistically significantly
correlated with the degree of measured passive hip laxity.
In addition the CHD prediction was shown to be
acceptably accurate in populations of puppies as young as sixteen weeks of
age. Moreover, the correlation between passive hip laxity and subsequent
hip DJD was shown to increase over the four-month figures when hips were
evaluated at six months and twelve months of age. In addition, no other
method used to evaluate CHD has undergone similar rigorous testing through
controlled scientific studies to determine diagnostic accuracy.
How does PennHIP
differ from evaluation methods, which use the Hip Extended Position?
PennHIP differs in some very fundamental and important
ways.
First, PennHIP was developed and tested following
strict scientific protocol and the results of these studies have been
published (and continue to be) in peer-reviewed, scientific journals. More
than a decade of research and analysis has produced a body of information
in support of PennHIP's effectiveness. As with all diagnostic tests,
PennHIP's accuracy is not 100 percent, but in direct comparisons it is far
superior to any other available diagnostic method.
Second, passive hip laxity is objectively measured
and the resulting Hip Evaluation Report is not issued in a pass/fail
framework. PennHIP specifically measures passive joint laxity and includes
the quantitative measurement in its report. Based on the degree of laxity,
the individual dog is then ranked relative to other members of the same
breed. (Note: Breed specific ranking's are given
when there are twenty evaluations - ranking is made to the general dog
population.) For example, a dog receiving a ranking in the 70th percentile
means that thirty percent of its breed members have hips that are tighter.
This allows breeders to easily identify those animals with tighter hips
within each breed. As shown in our studies, dogs with tighter hips are less
likely to develop CHD and pass that genetic tendency on to future
generations.
Third, because PennHIP is measuring maximal
passive hip laxity, the position of the patient is very different from the
hip-extended position. The hip-extended position has been used for more
than thirty years to screen hips for either DJD laxity or both. Laboratory
studies, however, have indicated wide diagnostic variability among radiologists
in interpreting this view. Further, through biomechanical testing, the
hip-extended view was found to mask the underlying true joint laxity and
through direct comparison, the predictive value for CHD was shown to be
inferior to the PennHIP procedure.
Most importantly, the heritability of the diseased
phenotype scored in the hip-extended view has not been studied in most
breeds of dogs. Knowledge of heritability is critical to determine whether
selection pressure will produce genetic change. Estimates for the
heritability of passive hip laxity drawn from analysis of full pedigrees
for the breeds examined thus far in the studies show high values (for
German Shepherd Dogs, heritability 0.61).
Fourth, the PennHIP method is based on strict
quality control. To take PennHIP radiographs, veterinarians must undergo
training and a certification process to demonstrate competency. The data
generated from PennHIP undergoes regular review and statistical analysis so
that useful information, by breed, is available to judge progress toward
reducing CHD. For optimal validity, it is mandatory that all PennHIP
radiographs be submitted for analysis and inclusion in the PennHIP
database. This policy eliminates the practice of pre-screening radiographs
and sending only the best for evaluation, resulting in biased hip data for
any given breed.
What happens to my
dog during a PennHIP Evaluation?
To obtain diagnostic radiographs, it is important that
the patient and the surrounding hip musculature be completely relaxed. For
the comfort and safety of the animal, this requires sedation, however, some
veterinarians prefer general anesthesia. Typically, three separate
radiographs are made during an evaluation. The first is a compression view
where the femurs are positioned in a neutral, stance-phase orientation and
the femoral heads are pushed fully into the sockets. This helps show the
true depth of the hip socket and gives and indication of the
"fit" of the ball in the socket.
The second radiograph is the distraction view. Again, the
hips are positioned in a neutral orientation and a special positioning
device is used to apply a harmless force to cause the hips to displace
laterally. This position is the most accurate and sensitive for showing the
degree of passive laxity. Passive laxity has been shown to correlate with
the susceptibility to develop DJD. A hip extended view is also included for
the sole purpose of examining for any existing joint disease such as
osteoarthritis. The PennHIP procedure has been safely performed on thousands
of patients.
What is the cost of
Having My Dog Evaluated?
The Veterinarian providing the service determines the
total fee for a PennHIP evaluation. It is important to remember that the
total service includes sedation, anaesthesia, three radiographs, office
consultation and all charges associated with mailing and film evaluation.
You will not find it necessary to write a separate cheque for evaluation
fees or mail your dog's films. The veterinarian performing the procedure is
responsible for payment and film submission, and will be able inform you of our current fees.
How Does this
benefit me as an owner or breeder of Dogs?
Scientific data confirms that the PennHIP method
surpasses other diagnostic methods in the ability to accurately predict
susceptibility to developing CHD. The method can be performed on dogs as
young as sixteen weeks of age compared with two years using the standard
technique.
The data generated by PennHIP will allow breeders to
confidently identify the members of their breeding stock with the tightest
hips. The PennHIP interpretation will also permit breeders to assess the
progress they are making with their breeding program as they strive to
reduce the amount of hip laxity in their dogs. Pet owners are able to
assess their pets risk of developing CHD, and make
their lifestyle adjustments for their dog, if necessary, to enhance the
quality of their pets life.
How can I get the name of a PennHIP Veterinarian to get
answers to additional questions?
If in the Melbourne metropolitan
area, contact Dr Ray Ferguson at the Monash Veterinary Clinic on 03 9544
7455.
If viewing this website from any other location and you need to obtain the
name of a veterinarian near you visit the PennHIP website. Locate
PennHIP Vets
Definition of
PennHIP Terms
Acetabulum - The
"socket" component of the hip.
Canine Hip Dysplasia (CHD) - A
developmental, degenerative condition affecting the ball and socket of the hip.
Conventionally diagnosed radio graphically by the presence of degenerative
changes and or subjugation of the hip. While the precise role of
subluxation in the development of CHD has been poorly studied and remains
controversial, radiographic evidence of osteoarthritis is undisputed
confirmation of CHD.
Certified PennHIP
Member - A veterinarian who has been trained in the PennHIP method
and has successfully passed the quality assurance exercises demonstrating
competence and repeatability in performing the PennHIP evaluation method.
Compression View - One of three
radiographic views taken during a PennHIP evaluation. During Compression,
the femoral head is pushed fully into the acetabulum. This view is included
for purposes of accurately indicating hip landmarks and to demonstrate
joint congruity, how well the femoral head fits into the Acetabulum.
Degenerative Joint
Disease (DJD) - A degenerative condition of the hip characterized by
one or more of the following: cartilage damage, joint effusion, synovitis,
periarticular osteophyte formation (bone spurs), subchondral bony
sclerosis, and ultimately bony remodelling. DJD is synonymous with
osteoarthritis and its radiographic presence in the hip is considered
diagnostic of CHD.
Distraction Index (DI) - DI is a
measurement of maximal passive hip laxity. It is a unit less number between
0 and 1. A smaller number DI means less laxity, (tighter hips) and less
susceptibility for DJD. A DI of .5 is interpreted to mean that the femoral
head is 50% displaced from the acetabulum. DI has been shown to correlate
strongly with a dog's probability of developing hip DJD.
Distraction View - One of three
radiographic views made during a PennHIP evaluation. Dogs are heavily
sedated or under general anaesthesia. A special "distraction
device" is placed between the legs with the dog on its back. The
device acts as a fulcrum to apply a harmless lateral distractive force to
the hips. The legs are positioned to optimize the measurement of passive
laxity. The amount of hip laxity is quantitated using the distraction
index.
Functional Hip
Laxity - Hip laxity or hip excursion that occurs during
weight-bearing activity such as walking, running or jumping. Functional hip
laxity is associated with the development of high joint stresses that cause
cartilage damage and ultimately DJD. While it would be very useful to know
the onset and magnitude of functional hip laxity, it is a dynamic condition
that is not possible to measure either clinically or experimentally.
Heritability - Heritability indicates
the proportion of phenotypic variation that is due to addictive genetic
effects. It expresses the extent to which phenotypes (for example, (CHD)
are determined by the genes transmitted from the parents. Heritability is
not a biological constant and will likely vary by breed. Higher
heritability means faster genetic change through selective breeding. The DI
phenotype is highly heritable (0.61 for German Shepherd Dogs) and indicates
that DI is a promising criteria on which to base
the selection of breeding stock.
Hip - Extended Position
- One of three radiographic views made during a PennHIP evaluation. The hip
extended position is included for purposes of evaluating the hips for
existing degenerative joint disease. It is not a reliable position for showing
true passive laxity.
Hip Laxity Profile - Hip laxity
profile refers to the "current" distribution of passive hip
laxity (D1) within a breed. It allows the breed or the individual dog to be
compared to other breeds or other individuals within the same breed.
Combining this information with radiographic evidence of DJD within a breed
facilitates a breed-specific determination of CHD susceptibility. In
addition, regular monitoring of changes in hip laxity profiles over time
permits an assessment of the progress of selective breeding attributable to
the PennHIP procedure.
Passive Hip Laxity - This refers to
the hip laxity that is measured in a dog that is sedated and non-weight
bearing. Since it is not possible to measure "functional hip
laxity", all hip evaluation methods assess (subjectively or
objectively) the magnitude of passive hip laxity.
PennHIP - PennHIP stands
for University
of Pennsylvania Hip Improvement Program.
PennHIP encompasses the overall evaluation method, the Network of
veterinary providers, analytical and support staff, as well as an extensive
database of hip and breed evaluation data.
Links - www.PennHIP.org
