Part 2: Your dog has hip dysplasia because your breeder watches too much ER and not enough House.

As a veterinary radiologist, I am routinely asked to evaluate screening hip radiographs in young patients as breeders and military and police organizations are attempting to “screen away” hip dysplasia in young patients. These breeders and organizations go to their veterinarian and ask for a “hip score” or “hip grade” or “hip screening.”  In most cases what they are asking for is an OFA evaluation of the hips as this is the most commonly requested and performed hip screening test.  The veterinarian complies then sends me the x-rays to help determine if the pet has hip dysplasia1.

The problem with all of this is that, even as a so-called “expert” in my field, using this particular screening test, I have no stinking idea if their pet has or will develop hip dysplasia or not.

Using the terms we learned in the first part of this series, the OFA hip screening x-ray test is not sensitive enough to identify all patients that will develop hip dysplasia in the future. Stated another way, this test is plagued by false negatives. Two recent articles highlighted some of the issues with OFA screening. On one article2 the authors concluded that young dogs with significant laxity were judged as OFA certified for breeding despite significant laxity and failed to identify osteoarthritis susceptibility in 80% of the dogs in the study that were judged normal by OFA. Ouch! A second article3 highlights the fact the OFA screening is a subjective test and the authors concluded that that there were discrepancies between observers grading OFA screening tests –  even among experienced observers. Ouch #2.

One positive thing that can be said about OFA screening is that this particular screening test is very specific for hip dysplasia. Stated another way, if the OFA folks say your dog has hip dysplasia you can bet it does.

The bottom line with all of this is that the lack of sensitivity (e.g. high false negative rate) using the OFA screening test means that we can breed two dogs with excellent hips and their offspring will develop hip dysplasia.

Using the OFA test is better than not testing at all but there is another test that is more sensitive and more specific to identify and predict the development of hip dysplasia in young patients. That test is called PennHIP.

Previously we said that tests that are more sensitive and more specific are often more expensive and/or more of a hassle to run4. The case is no different with PennHIP. Unlike OFA where any vet in any practice can run the test,  with PennHIP veterinarians require additional education and must be certified before performing this test. Obtaining a PennHIPevaluation is also more expensive for breeders as sedation is required to perform the examination. Moreover, many pet owners will request an OFA grading score before purchasing a puppy (most pet owners do not know about PennHIP and need some education on the topic) so breeders are now required to do two hip screening tests to make the owners happy and to do their very best to work toward decreasing the incidence of hip dysplasia in our pet population.

 

Take home message #2: The slight extra cost associated with the Penn Hip evaluation is worth every penny.
Please take this series of article as a plea to all breeders and pet owners to help increase my job satisfaction and relieve me of the pain of trying to attempt to predict which patients will develop hip dysplasia by using poorly designed imaging tests. Please spend the money, sedate your pets, and get a PennHIP evaluation if you really want to know if your dog will develop hip dysplasia or, if you will be breeding your dog, if your dog has propensity to have puppies with hip dysplasia.

 

My highly opinionated recommendations: The bottom line with all of this is that if I ran the world I would require

 

  1. Breeders to stop requesting OFA projection radiographs in young patients
  2. Pet owners to stop asking breeders for OFA grading scores.
  3. If an OFA test is performed and it is negative, a PennHIP test would be performed as a follow up test to rule out a false negative.

 

NOTES:

1. The problem with this situation is that pet owners get upset that they have to run test after test. They often think the vets does not know what they are doing when they get contradictory results or get upset that the vet is spending their money

 

1. one of the limitations of OFA screening and the OFA database is that pet owners are not required to send in the images of pets screened for hip dysplasia. In many cases if the hips are terrible they do not send in the films. This skews the data the OFA keeps about hip dysplasia toward the best pet owners and vets who send in the images regardless. This is what they are supposed to do but it does not always happen.

 

2. Evaluation of the relationship between Orthopedic Foundation for Animals’ hip joint scores and PennHIP distraction index values in dogs. J Am Vet Med Assoc. 2010 Sep 1;237(5):532-41.

 

3. “The Effect of a Technical Quality Assessment of Hip Extended Radiographs on Interobserver Agreement in the Diagnosis of Canine Hip Dysplasia” Vet Radiol Ultrasound. 2010 Sep-Oct;51(5):498-503.

 

4.  The majority of veterinarians are not currently certified to perform a PennHIP evaluation because pet owners and breeders are not asking for the test so it does not make financial sense for them to get certified to perform the test.

 

About the author: Dr. Matt Wright DVM MS DACVR is a veterinary radiologist who sits in a dark room looking at x-rays all day long. Although he feels that his essays are well thought out, his opinions often fall outside the mainstream. The ideas and concepts in his essays are his and only his and do not necessarily reflect those of his clients, colleagues, or employer. He is the author of several books including Breedfreak – The Dog Breed Guide for Normal People with Real Lives, Families, Houses, and Budgets.