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Animal Medical Hospital
Canine Hip Dysplasia
Why my dog? I must be cursed.
Curses aside, there isn't really a single, good answer to why some dogs develop dysplasia and others (even in the same litter), don't. We know that some of the influence is genetic, but the genetics themselves aren't simple. It certainly isn't as easy as saying, "a dog with good hips will have puppies with good hips". We've seen puppies with terrible hips come from parents with excellent hip conformation. We've seen dogs with good hips come from parents with bad hips. The best we can say is that there is a "genetic predisposition to developmental problems" in some animals. Not every dog with this predisposition will go on to have problems.
Another factor is breed or size. Hip dysplasia can be found in any breed and any size of dog. However, large breed dogs are over-represented when we talk about clinical hip dysplasia. More jargon for you, eh? That only means that lots of dogs have malformed joints (dysplasia), but large breed dogs seem to be more disposed to showing clinical signs of lameness and pain, and developing arthritis. The smaller breeds often go their whole lives with icky-looking hips on x-rays and never show any signs of trouble.
Why is this? A lot of it has to do with wear and tear. A 50 kg Newfoundland will be putting a lot more force on the joint components than a 3 kg Chihuahua. Over a lifetime the Newf will tend to do more "abusive" exercise and have to heave that giant frame around. All of the joints will be at increased risk for trauma, impact injuries and strain injuries simply by virtue of the enormous forces.
This ties in with nutrition. If you learn nothing else from this site, remember that fat dogs get arthritis. It really is that simple. Purina did a beautiful study in which they raised 48 Labradors from puppyhood to death in old age. Half of the puppies were fed enough food that they were somewhat overweight. The other half were fed so that they were in the ideal weight range. Aside from living an average of 2 years longer, the slim dogs had far less arthritis.
They x-rayed all of the dogs at age five and found that about 9% of the slim dogs had arthritis changes in the hips already. That seemed like a lot to me until I read that 43% of the fat dogs were arthritic. Wow! The only difference between the two groups was weight. Exercise, housing, and food type were identical. Weight alone caused over a four-fold increase in arthritic change in the hips.
How do we prevent this from getting worse?
We can apply all of our knowledge when it comes to feeding puppies. Some people used to push large breed pups to grow fast and big. They wanted big dogs, so they wanted big puppies. The results were not good. Depending on the supplements given and the general nutritional levels, there was asynchronous growth. This means that one part of the system grew too quickly or slowly. We know that in order for a joint to form normally we have to get coordinated growth of the bones, muscles, ligaments, cartilage, and all of the other structures. Get any one part out of whack, and you have dysplasia.
We are smarter now. Instead of pushing growth, we want to slow things down and give the joints a chance. One excellent option we have now is the new "large breed puppy" or "adolescent" foods. These are formulated to get good growth without over-supplying any one nutrient, hopefully minimizing the risk of dysplasia and puppyhood obesity.
As well, one study was done showing that a puppy's risk of hip dysplasia is halved if he is fed meals rather than free-feeding. This may tie in to the obesity issue, since free-fed dogs have more of a tendency to be fat.
"Doc, how do I know whether my poor puppy has hip dysplasia?"
There are several ways to tell whether a pup is going to have issues with hip dysplasia. One is simply to watch the puppy run and walk. All puppies walk a little "funny". They have big feet, they trip over them, and they have that cute little butt-wiggle. But older puppies who are getting dysplasia will 'bunny hop' when they run. They will bring both hind feet forward at the same time, putting a hitch in the gait and making it look a little odd. This is beyond the usual loose look of a normal puppy. Watch for any change in your dog's running or walking style.
You can also get your vet to do something called an Ortolani test. This is a simple test to try to determine whether there is an excess laxity in the hip joints. It can be done on most young puppies during a routine examination. Sometimes if the pup is very wiggly it is easiest to do it when they are anesthetized. At AMH we always take advantage of the total relaxation during general anesthesia when a pet is spayed or neutered to perform an Ortolani test. Every dog that is under anesthetic and had not been previously check has his or her hips palpated.
We can also pelvic x-rays on animals we suspect of having hip dysplasia, or who have a positive Ortolani test, or just for peace of mind. A PennHIP x-ray is a specialized kind of x-ray that uses different positioning and is of more use in determining the exact degree of laxity in the hips. The PennHIP distraction index correlates extremely well to the development of arthritis. High distraction index (loose hips) = high risk of arthritis. PennHIP radiographs can be done at any time after 16 weeks of age. The evaluation does not change significantly with time or maturity, making it an excellent screening test for future problems.
We can do routine x-rays of the pelvis at 6 months and 2 years on dogs who are going to be used for breeding purposes, or who need their hips "certified" for another reason and owners do not want to do PennHIP studies. These x-rays are then sent to the Orthopedic Foundation for Animals (OFA) or the University of Saskatchewan for evaluation and grading. These grades are sometimes advertised when puppies are sold. "Both parents OFA certified excellent hips and elbows" for example.