The questions "PUPscan" won't answer. Part 2: The answers

By Carol Beuchat PhD
Yesterday's post was about a new venture in the UK called "PUPscan", which endeavors to identify puppies that will develop hip dysplasia as adults on the basis of a sonographic examination of the hips in puppies 6-8 weeks old. The gist of my discussion is that I had basic questions about what they were measuring and the scientific evidence to support assertion that their scans would be predictive of hip dysplasia in the adult. They did not provide answers to these questions despite repeated attempts to extract basic information from them.

• What "measurements" are taken?
• What evidence is there that whatever you are scoring is predictive of the development of hip dysplasia?
• What value is there in imaging a cartilagenous joint that is yet to be formed?
• What is the basis for your claim to be assessing "congenital genetic dysplasia"?

If you haven't already, you can read my earlier post here.
Last night, I was alerted to a paper (Fischer et al, 2010) that examined the efficacy of using ultrasound of puppies to predict hip dysplasia in adult dogs. This is the very thing they appear to be doing, so the results of that study are worth a closer look.
They examined 566 puppies of 17 different breeds, from age 16 to 49 days (mean = 32.5 days). They clearly describe the measurements they made, which included α-angle (as illustrated), as well as a measure of joint laxity (distraction value, DV). They also assessed the repeatability of their measurements and subjected the data to rigorous statistical analysis. They note that they did not record β-angle as had been done in other studies because of low repeatability. Of the animals they examined as puppies, 203 (35.9%) were radiographed as adults for classification of hip status.

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Their results:

"...No statistical significant correlation could be found between sonographical determinations of α-angle, joint laxity, DV and conventional radiographic hip joint classification at the age of 12 to 24 months...None of the
parameters assessed by ultrasonography in puppies could ultimately be linked to adult CHD. Results of our study suggest that static and dynamic ultrasonography of hip joints in puppies between 16 and 49 days of age is technically feasible but cannot be recommended for detecting puppies that will develop CHD between the ages of 12 and 24 months."

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Their conclusion is very clear. They were unable to predict the development of hip dysplasia based on ultrasound examination of young puppies. Further, they note that similar sonographic assessments have been done on newborn infants to detect dysplastic or immature hips for many years. However, they note that the hips of puppies always appear normal at birth and dysplasia develops postnatally, so the structural anomalies in newborn infants are not evident until later development in puppies.
There is one question I asked that is not answered by this study:

• What is the basis for your claim to be assessing "congenital genetic dysplasia"?

PUPscan claims to be able to distinguish "genetic" dysplasia from dysplasia resulting from trauma or damage. In fact, as Riser et al (1985) explain, the hips of all puppies are anatomically normal at birth, and hip dysplasia is the consequence of abnormal stresses on the structures of the hip that result from laxity in the joint. That is, there is no "genetic" hip dysplasia in which genes are responsible for misshaping of the hip during post-natal development. Rather, hip dysplasia is in fact the result of trauma and damage because of abnormal biomechanics. He notes that genetics does play a role in the body conformation of a dog (e.g., size, weight, muscle development), and these features are related to breed-specific differences in the prevalence of hip dysplasia, with large, heavy dogs being at highest risk. From this,
To be fair, assessing joint laxity in young puppies seems like a reasonable idea. In fact, I've given it some thought myself, and I haven't ruled out the possibility that it might be a useful thing to do. While this study failed to find that any of the things they measured were predictive, it's possible that focusing on a single breed (instead of combining the results from 17 breeds) might reveal something missed in this study.
The bottom line

A published, peer-reviewed study failed to find any evidence that ultrasound examination of young puppies was predictive of the development of hip dysplasia as adults.

Finally, this post appeared on the PUPscan Facebook page today:

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REFERENCES

Fischer A, A Flock, B Tellhelm, K Failing, M Kramer, & C Thiel. 2010. Static and dynamic ultrasonography for the early diagnosis of canine hip dysplasia. Journal of Small Animal Practice 51: 582-588. DOI: 10.1111/j.1748-5827.2010.00995.x.

Riser WH, WH Rhodes, & CD Newton. 1985. Hip dysplasia. Ch 83 in Textbook of Small Animal Orthopedics, CD Newton, Ed. Lippencott Williams & Wilkins.

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