04 Canine Hip Dysplasia: How Does PennHIP Differ from Evaluation Methods Which Use the Hip Extended Position?
Description
This article is from the Canine Hip Dysplasia FAQ, by rpd-info@zmall.com (Cindy Tittle Moore) with numerous contributions by others.
04 Canine Hip Dysplasia: 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 rankings are given when there are twenty or more evaluations.
If there are fewer than 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. A knowledge of
heritability is critical to determine whether the 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 prescreening radiographs and sending only the best for
evaluation, resulting in biased hip data for any given breed.
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