POINTS EAST WEST VETERINARY SERVICES
Sports Medicine and Rehabilitation Specialty Practice
Dr. David Lane, DVM, ACVSMR
PENNHIP X-RAYS TO DIAGNOSE HIP DYSPLASIA
Canine Hip Dysplasia is a well recognized genetic condition in dogs that can cause hip arthritis, chronic pain, and sometimes requires surgery. Over the last fifty years, breed organizations and kennel clubs have attempted to remove the disease from the population through selective breeding. Despite this effort, little progress has been made. This may be in part due to the under utilization of the PennHIP radiographic technique.
Selecting dogs that are considered “hip dysplasia free”, those considered unlikely to pass the condition onto their offspring, has largely been based on their OFA radiograph findings – by x-raying the appearance of the hips while the dog is lying on its back with its legs in full extension. Unfortunately, research has shown that OFA radiographs are a poor test for screening against hip dysplasia.
OFA radiographs are a poor test because although they select for dogs with good hip conformation, they does not test for soft tissue laxity, a key component in the development of hip dysplasia. As a result, many dogs that pass their OFA radiographs have now been shown to have lax hips This is likely the reason that efforts to eliminate the disease have not worked. Research has found that breeding dogs with passing OFA radiographs results in hip dysplasia in anywhere from 19% to 73% of the offspring.
PennHIP radiographic testing was introduced over 20 years ago, and tests both hip conformation (as does OFA) as well as tissue laxity. It is a more sensitive test than OFA radiographs, meaning that it will detect cases of hip dysplasia that otherwise would be missed. In order to breed hip dysplasia out of the gene pool, it is key that all dogs potentially carrying the condition are detected, and therefore the test needs to be as sensitive as possible.
Side by side comparison of OFA and PennHIP radiographs found that none of the dogs that failed their PennHIP radiographs, passed their OFA radiographs, but many dogs that passed their OFA radiographs, failed their PennHIP radiographs. In fact, two of the dogs with “excellent” OFA ratings had some of the worst PennHIP scores, indicating a high probability of developing hip arthritis secondary to tissue laxity later in life.
Another limitation of OFA radiographs is that scoring is based on subjective evaluation. This means that the same radiographs may get a different score depending on who is reviewing them, or even if the same radiologist reviews them on different days (with a different mood, fatigue level etc.). This problem is reduced with PennHIP radiographs because the results are based on measurements and the calculation of a distraction index, which is less likely to show variation between radiologists.
OFA radiographs require the dog to be at least 2 years of age before testing, whereas PennHIP radiographs have been shown to be accurate in predicting the onset of hip dysplasia as early as 4 months of age, allowing for earlier testing.
Conservative estimates based on mathematical models indicate that for a breeder of Labrador retrievers hoping to eliminate hip dysplasia from their line, using the PennHIP system will accomplish that goal 4 times faster than by relying on OFA radiographs.
Although some dogs receiving OFA radiographs may not need sedation, sedation is mandatory for PennHIP radiographs in order to relax the muscles enough to properly appreciate the degree of connective tissue laxity.
Any breeder who is serious about producing a line of dogs free from hip dysplasia should employ a PennHIP screening program. Pet owners and dog handlers who want to invest in a dog suited to an active life style, working, or competition, should also consider only purchasing PennHIP cleared dogs. Dogs can be tested for hip dysplasia using the PennHIP method as early as 4 months of age.