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Why Do Large Dogs Get Hip Dysplasia?

Why Do Large Dogs Get Hip Dysplasia? If you have owned several large dogs, you may have wondered why big dogs get hip dysplasia and how you can prevent them from getting this debilitating condition. Actually, to be correct, not all large dogs are prone to hip problems. There are certain large dog breeds that are curiously almost immune to hip dysplasia. Before you head out to buy a small dog in hopes of not encountering future hip problems, consider that small and medium-sized dogs are prone to their own set of orthopedic problems, and some of them may even have a higher incidence of hip problems compared to some larger dogs.

The Role Of Hips

The dog's hips connect the bones of the hind legs with the pelvis. Composed by the femur bone and the acetabulum, the hip joint is medically known as the acetabulofemoral joint. This ball and socket joint is one of the most important joints found in the dog's body. The primary role of a dog's hips is to support the dog's weight and allow stability whether the dog is standing or in movement.

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Normal Hip Anatomy

To better understand hip dysplasia, it's important to understand the normal anatomy of a dog's hips. In a dog with good hips, the spherical end of the femur bone fits snugly into the concave socket of the pelvis (acetabulus). The surfaces of both joints are covered by a slippery tissue called articular cartilage, which is lubricated by a thin film of synovial fluid, a fluid with an egg-white consistency whose purpose is to reduce friction between bones during movement.

Hip dysplasia on x-ray

Hip dysplasia on x-ray

Abnormal Hip Anatomy

In a dog with hip dysplasia, the femur does not fit correctly into the pelvic socket, triggering a cascading chain of problems. Because the fit is not as snug as it's supposed to be, there is increased wear and tear as the dog moves. This leads to the development of secondary degenerative joint disease, pain, lameness, and eventually debilitation.

A Matter of Nature

When it comes to hip dysplasia, there appears to be a strong genetic component at play. Hip dysplasia is known as being an inheritable condition taking place when defective genes are passed from one generation to another. For this reason, reputable breeders are very careful in having their breeding stock tested for good hips before being allowed to reproduce. By carefully screening for bad hips, breeders can reduce the incidence of passing down genetic problems from one generation to another. Completely eradicating the disease from a specific breeding line can be challenging at times.

A Matter of Nurture

Other than genes, the environment in which dogs who are genetically susceptible to hip problems may act as an aggravating factor to hip problems. The amount of calories a dog consumes and increased body weight have been known for increasing the severity of hip problems in genetically susceptible animals since extra weight contributes greatly to the degeneration of the hip joints in a dog. Rapid growth in puppies and strenuous exercise at a young age are other contributing factors. According to the Baker Institute for Animal Health slowing down the growth rate during a puppy's early months of life can, not only lessen the severity of hip dysplasia, but possibly even prevent it. Interestingly, according to Wayne H. Riser, hip dysplasia has not been reported in wolves and foxes, and this is likely because they are slow growing and late maturing species.

The Role of Body Type

Breeds most commonly affected by hip dysplasia include German Shepherds, Rottweilers, Golden Retrievers, Great Danes and St. Bernards. Why are large and giant breeds overrepresented when it comes to this condition? Body type seems to matter. According to Dr. Frank Borostyankoi, a Diplomate of the American College of Veterinary Surgeons this is likely due to the fact that in these breeds more stress placed on the ligaments and joints because of their body weight.

Exceptions to the Rule

Interestingly, there are several large dog breeds which are less predisposed to hip dysplasia. According to veterinarians, Dr. Foster and Smith, sighthounds such as the Greyhound or the Borzoi have a very low incidence of hips dysplasia. Why is that? Dr. Frank suggests that it's likely because greyhounds and whippets are lightweight breeds. However, according to the Textbook of Small Animal Surgery, Volume 1, while these breeds are at lower risk for hip dysplasia, it doesn't necessarily mean they are exempt from developing it.

Not only Large Dogs

Surprise! Pugs rank second place for bad hips.

Surprise! Pugs rank second place for bad hips.

According to board-certified veterinary surgeon, R.D. Montgomery, dogs of all breeds and sizes have been found to have hip dysplasia and even some relatively small dogs like the American Water Spaniel have a very high incidence of hip dysplasia. If we look at statistics provided by the Orthopedic Foundation for Animals, we may be shocked to see that the bulldog, a breed weighing about 50 pounds is at the very top of the list as the dog breed with the highest frequency of dysplastic hips, while second place is held by the pug, a dog breed merely weighing in at 20 pounds!

Did you know? According to the Institute of Canine Biology, all dogs are born with a normal set of hip joints at birth. Things start to deteriorate when the congruity between the femoral head and the acetabulum is disrupted.

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