We sent Diva in for a PennHIP exam yesterday.  Dr. Temm took some digital pictures of the x-rays so I could show you in this blog post.  I wish I'd have taken some other pictures, but didn't think of it at the time.

The first thing they do is put your dog under anesthesia.  Here's something to consider when talking to your veterinarian about putting your dog under on gas.  Sevoflurane is used in human medicine and is less irritating to the lungs than isoflurane.  Isoflurane is cheap but now only common in veterinary medicine.  Sevo is the better drug.  Find out which your veterinarian uses, and you'll get some insight about him or her.

With the dog out, she is propped in a plastic saddle that keeps her on her back.  This is all standard equipment for veterinary radiology.  The veterinarian or technician will use a measuring stick type of device to determine the exposure time.  It's based on the thickness of the animal.

The first image is taken while pulling the legs parallel to the table, straight back.  This is the only image the OFA uses.  It looks like this:



Keep in mind this is a photograph of a radiograph.  It's not a digital radiograph.  These images are a little fuzzy.  What you can see here is that she has round "ball" joints and deep and round "sockets" and that everything seems to fit very well.

Dr. Temm takes this image and lays the mysterious PennHIP device on it so that he can adjust it to the right width.  OK, I have heard a dozen different descriptions of this thing.  It is not a vice, there is no mechanical pressure put on the dog's hips.  It is only used so hand pressure can be applied to the hips.  Here is a picture of the actual device. 



The slotted end pieces are either aluminum or something a lot like aluminum.  The knobs are plastic.  The rods are clear plastic wrapped in foam.  There is a number in the rod that shows up on the x-ray.  I presume this is to match the veterinarian to the device. 

The next picture is taken with the knees up.  The ankles are twisted to drive the hips into the socket.  I'm sure this would be uncomfortable, but not terribly painful.  The power on the x-ray machine has to be turned up (usually about 20%) because the thigh muscles are in the way.  The picture is shot through the thighs lengthwise.  In Diva's case, it had to be turned up 30% because her muscle is enormous and dense.  Here's the result.



Again the real x-ray film is easier to read.  The massive clear spots are from her thunder thighs.  However, you can see the heads of the joint are driven into the sockets.  It's hard to see here, but they do fit very nicely.

Next, Dr. Temm took the spreader and put it on Diva's belly and a second assistant held it in place.  He used the same kind of pressure, but now with the leverage against the padded tool, the sockets go out instead of in.  You can see it's "shadow" in the x-ray below.  It's about as wide as the tip s of the pelvis and runs over one hip joint and just to the right of the hip on the right (Diva's left hip, she's on her back, remember?).



You can see they didn't move much, and that's the whole theory behind the Distraction Index.  A hip with a DI of .50 comes out of the socket by 50%.  They find almost no dysplasia in dogs whose hips only come out 30% or less.  Dogs whose hips come out 80% or more almost always have dysplasia.  The dogs in between, the tighter they are, the less likely, the looser, more likely.

The x-rays will be sent to the University of Pennsylvania to be read and measured by their radiologist.  There is no "interpretation" the score is a measurement. 

So if you are in the middle, what are the other factors involved?  Well every structure, be it a house, bridge or yes a dog, is made of materials, geometry and joints.

Geometry plays a huge role in the stress put on the hip joint.  Basically the shoulder blades and hips should align at about a 45 degree angle and should  be symmetrical.  A lot of dogs have very straight fronts and rears and that means their bad proportions put extra stress on the joints.  Unfortunately you can't do anything about geometry, it's heritable, just like the hips.

A dog's joints are mostly bone, right?  Yes and no.  It's the ligaments that hold the hips in the sockets, in concert with a sack of fluid.  But muscle plays a big role too.  Think of a dog's shoulder.  It's held in place completely by muscle attached to the shoulder blade.  If you have ever cut up a deer, it's the same.  No collar bone.  So having good muscle tone will probably help keep a joint that isn't perfect intact.  That's something you can control, especially if you have the screening done young enough for you to do something about it.

The final thing that makes structures fail is the load.  If your dog is fat, it's carrying more load on the weak joint than it should.  I have a terrible time with my weight, but my dogs are thin.  I don't care if they "look" hungry.  I just measure their food every day.

If you have read a bunch of negative stuff on the net about PennHIP, check the dates.  Most of it is over ten years old, there is no controversy anymore.  Dr. Gail Smith originally bought the license from his university employer to "sell" this service as a for-profit endevor.  The advertising was brash (coed's on campus loved the "Tighter is Better" tee shirts, I'm told).  Folks with OFA excellent dogs suddenly discovered their PennHIP scores were middling at best.  Couple it with a young interenet where anybody could (and still can) say anything, but it all seemed so much more autoritative back then because it was still pretty difficult to actually publish a web site.

PennHIP is currently the best, most predictive method available.  I will remain loyal only as long as it remains the best method.