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PennHip vs OFA, A Personal Story

By F. Lynann Stuby

 

Let me begin by saying I am a member of the Health Committee of the GPCA.  I spent most of my life in nursing, in specialty units in a major metropolitan hospital. I have always had an intellectual curiosity about most things,  and in particular medical things.

I had heard of  this new hip testing procedure for Dysplasia, and after reading their web site felt it to be potentially more beneficial for breeders. My beliefs were based on several things.  First was that this procedure used several views, rather than one, of the dogs hips. Second was that it was read by a computer thus removing any “opinion” from the mix as is seen in the OFA readings. And third it could be done at a young age, long before you would have a lot of money tied up in a dog whether it was for conformation, obedience or service work. Wow, what a great thing for the dog world. I believed in this so strongly I encouraged my vet of 25 years to become certified and he did attend the seminar, after a year or so of my prodding.  My vet has remained on the cutting edge of new techniques and equipment as they have come along over the years, and has a thriving practice with many “breeders” like myself who travel a distance to go to his clinic.

I had seven bitches of all ages that I wanted to PennHip.

He attended the seminar in January and I had high hopes of having all of my dogs PennHip evaluated by the end of January no later than February.

As it turned out, the certification procedure involved  five “test” exams be perform by each new practitioner, each exam taking five views. These are then evaluated for their technique before a certification is awarded.  

My vet had my dogs ready and waiting to be used as his first “subjects.”  All five had to be completed before any of them are “officially” read and numbers issued to either the vet, or the owner.   I could live with this even if it might drag things out a little.  I could not have foreseen that the last result would be arriving in June. Due to a long term patient/ client relationship,   I was allowed to witness every single examination performed. A great learning experience for me as well.

The premise from the PennHip research/method which has been ongoing for many years and now includes 63,000 dogs in their data base, is the laxity or “looseness” of the joint being a very accurate prognostication of potential Hip Dysplasia. The numbers have proven out and this can be done on dogs as young as 16 weeks old with good  reliability. The procedure consists of three views,  a extended view, (OFA view), a compression view, which simulates the dog standing, and a distracted view which pulls the hips from the socket as much the tendon and joint capsule will allow showing “passive laxity.” This distracted view has a device that is used to leverage the hips from the sockets. The dog must be totally sedated.  Unlike OFA, once an exam is done and it ‘”appears” like a potential poor reading might ensue, the practitioner is mandated to send the exam in. Thus all exams are included in their database, and the potential for the “bad” results to be removed from the figures does not occur.

Let me take this opportunity to explain a phenomenon that can occur with this examination. That is cavitation. The very best explanation of this I could find was in the following article. Here is the  excerpt on cavitation from

New Words in the HD Dictionary by Fred Lanting.

Cavitation
A word very few will come across when using the advanced PennHIP
evaluation is "cavitation". The space between the acetabulum and the
femoral head (the socket and the ball) has a small amount of lubricating
liquid called synovial fluid that performs a function similar to that of
the grease in your car's ball joints. However, it also apparently has
another critical function, and that is related to the fact that it is
permanently sealed in, and if you were to try pulling the ball out of its
socket, there would be a vacuum-like effect. The harder you pull, the
harder it resists. Of course, if you puncture that joint capsule, you
would let in some air or fluid, and the "vacuum" would be lost. Likewise,
if the dog had a genetic defect that allowed production of excess
synovial fluid, the negative pressure would not be as significant, and
you'd be able to pull the ball further out before resistance built up. In
order to get a good reading of the difference between compression and
distraction views, and measure the displacement to give that index, the
vet has to exert a considerable force, up to the point where even more
force no longer produces any more displacement. The limit to which he or
she can pry the bones apart illustrates a principle of physics and
mechanics known as Hook's Law. A spring or elastic material can be
stretched with relative ease up to the point of its elastic limit, and
will stretch no further, no matter if you add one ounce to the weight or
100 pounds. Of course, if you put a ton or so on the steel cable or
spring, you might exceed the elastic limit and the steel will fail, and
not regain its length the way it did when you stayed within the limit and
relaxed the tension.
In distracting a dog's hip joint, a slightly similar thing happens, but
you do not go past the yield point the way you can with an enormous
weight on the steel test piece. Instead, something else "gives", a
temporary and harmless phenomenon that is quite rare (about 4%) in the
distraction procedure: voids appear in the synovial fluid and give a
sudden decrease of pressure in the articulation area. Nitrogen and/or
other normally-dissolved gases in the fluid are subjected to enough
suction force that they vaporize, and can show up as radiolucent areas on
the radiograph. When it happens, it is almost always only one hip that is
involved. Within minutes to an hour, they re-dissolve and the dog can be
re-tested. If it takes longer than the vet wants the dog to be under
anesthesia, the PennHIP evaluators in Philadelphia will just take the DI
reading of the other hip. In the even less frequent instance of a vet
causing cavitation in both sockets, that film is rejected or the vet has
already realized what he did, and repeats that part a little later.  A
similar pop or snap happens when one cracks his knuckles, and it takes a
while before it can be done again. I've been annoying family members that
way for fifty years with no damage, and there is likewise no damage to
the dog when cavitation occurs.

So now you know as much as I do about cavitation.  Once this occurs there is not a number score given as this can drastically change the reading toward the negative. RECOGNITION of cavitation is essential for an accurate reading. Even “partial cavitation” can cause a very different reading to be given.  The decision of whether to read or not to read, is done at PennHip. A human decision, whether the computer should read the film. There is not any other circumstance that can occur during  the exam that can result in an inaccurate result other than inadequate distraction, that I am aware of. This is also a judgment call from those at PennHip.  

I have PennHip exams on eight of my dogs.  I as well have done OFA certifications or prelims on five of them at the same time. The OFA view (extended) is done in the PennHip exam, so I originally thought why not. I had also seen some websites of other breeds where both were done and the results were very inconsistent, high positive outcome using one method while negative outcome is reported with the other. I assumed it was just a bad day for the OFA viewers on those occasions, as PennHip is read by a computer, and not subject to “human opinion.”  I have learned this is not necessarily the case.

I received several scores that were very discouraging, like half of my bitches had hips scores in the area that I did not really want to breed them. The worst, was one of my imports with quite a sizable investment in her already. I had decided to choose one of these bitches and let the others go to pet homes, no matter what I had invested in them. There were a couple that the PennHip score coincided with OFA , as well as siblings in the litter.  There were several where they did not coincide with the OFA grade, and pedigree would not have suggested poor hips. I have been very cautious to purchase good breeding stock, with hips and eyes well documented in the pedigrees. I made the decision to take two, with unexpected poor results, to another vet who was very experienced in the PennHip method and technique.  

The two that I had re PennHiped both came back better than the first exam. On one exam, PennHip phoned the vet who did the re-exam, and discussed this very different reading with her, and they felt after re-examination and comparison of the first set of films with the second, that one of the hips were at least partially cavitated. This same bitch had a Good OFA prelim.  At the same time, a pet that I have, returned with a Good OFA reading, and a reading of .30 and  .50, with a note attached stating that partial cavitation of the .50 hip was strongly suspected.  I wondered why a reading was given at all, if it was noted to be partially cavitated.   At this point I had gone from the depths of doom, looking at placing thousands of dollars worth of breeding stock, to at least seeing some light at the end of this tunnel. One bitch at this point who had two Fair OFA evaluations, and PennHip scores indicating that she was a moderate to low fair was placed. 

Annie's Story.  On the initial five certifying tests, she was the only one that PennHip asked my vet to do over, as “there was no difference between her compression and distracted view.”  To toss another  wrench into the mix, my vet had installed new digital system for his x-ray equipment. We did the second procedure, and fell victim to new computer equipment syndrome, they accidentally were deleted.  So back again for a third set. By this time, Annie was beginning to glow in the dark.  We did these and in looking at them in the office,  there appeared to be a large amount of distraction. Her scores came back, . 67  .65. These readings are indicative of a dog that would likely be affected at a young age with Hip Dysplasia. Again doom has struck my kennel. I had actually talked with possible new pet owners for her.  

I decided to have her reexamined when the OFA prelim reading came back GOOD. How could this be? My vet was kept aware of all of the numbers on the others I had done elsewhere. He volunteered to do yet one more set of films. When we arrived it was decided that we would do five views, the extended, the compression, and three distracted, one with a slight pressure used, a “normal” pressure used, and the last would be with enough pressure to cavitate the hips.  He would contact PennHip and discuss this with them, and let them know why the extra views.

This last set returned .42 .42. A huge difference from the previous set which returned so horrible.  Considering the quality of this particular bitch, this  reading was acceptable to keep  her in my breeding program. 

 My conclusions to this entire experience.

Technique is of the utmost importance, as it seems in novice practitioners, cavitation is slightly more likely to occur.

There is a human judgment element involved with PennHip, as the detection of cavitation, complete or partial, must be accurately determined before the computer is asked to read the distraction score.

I will always send in an OFA with the PennHip, if they are drastically different, there just might be a reason for it.

Will I continue to PennHip? Yes, because within the three grading levels of OFA, there is a range,  and PennHip gives such an exact number. It will tell you whether you have a low or high excellent, low  or high good, a low or high fair. The more information available to use in our breeding decisions, the better.  A graph is presented of all of these readings.

 

 

 

Dog Sex

Age

Novice PH

Practitioner

% Tile

Experienced

PH Practitioner

% Tile

OFA

Grade

F

17 weeks

L .37 R .32

80

-

-

-

 

F

18 weeks

L .45 R .47

(R Cv. Found later)

 

60

L .40 R .30

80

GOOD

Prelim

F

18 months

L .45 R .40

60

L.45  R.35

60

FAIR

Prelim

F

18 months

L.35 R. 35

90

-

 

-

 

F

23 months

L.47 R .53

50

-

 

FAIR

Prelim

F

13 months

L 67 R .65

20

L .42 R .42

70

GOOD

Prelim

M

23 months

-

-

L .32 R .32

90

 

 

F

36 months

L .30 R .50

(R Cv. Suspected)

50

 

-

 

GOOD

 

 

My gratitude to Fred Lanting for the use of his article on Cavitation.

 
 
   
   
   
   
 
   
   
 
 
   
   
contact information

F. Lynann Stuby
phone: 317-831-7887
email:
click here

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