Hip dysplasia (HD) is an inherited developmental disease. Dogs who inherit the genes for HD become dysplastic when the muscle mass that supports the hip joint does not mature at the same rate as the skeleton. The resultant disparity between soft tissue strength and biomechanical forces during skeletal growth gives rise to varying degrees of a shallow hip socket and a flattened femur head. This results in ill-fitting or loose hip joints and the development of secondary osteoarthritis (joint inflammation and degeneration). Bony changes develop because the muscles lack sufficient strength to keep the hip joint stable.

Symptoms may vary from mild lameness of the hindquarters to severe pain and inability to walk. In dogs with strongly developed hindquarter musculature there may be no external symptoms at all. However, when the muscle mass decreases in old dogs, chronic pain and stiffness will develop.

The only definite way of determining whether a dog has HD is by means of radiographs (x-rays). Dogs must be at least 12 months old when x-rayed and a specialist veterinary radiologist must evaluate the x-rays. In South Africa hips are graded according to the FCI grading system. (refer table appearing elsewhere)

NORMAL HIPS

The two hips of a dog may have different grades, eg A1-C1 or B2-D2. The grading system is merely a description of the physical appearance of the hips on a radiograph. The grade does not necessarily reflect the severity of clinical symptoms or the degree of chance of a dog transmitting the disease. A dog with C2-C2 hips has as much chance of transmitting the HD-genes to its offspring as a dog with hips graded E2-E2. The transmission of the genes from parents to offspring is complicated, as it probably involves several genes.

A dog with normal hips is not necessarily genetically normal and may transmit the disease to its progeny. Two radiologically normal parents may therefore produce affected progeny, which means that we will never be able to eliminate hip dysplasia completely. In addition, the severity of the disease in dogs that do have the genes may be influenced by certain environmental factors such as overfeeding and strenuous exercise at a young age. The environment cannot however cause the disease in genetically normal animals - the dog must first have hip dysplasia for environmental factors to make it worse.

Because of the above, breeders who wish to improve hips in their breeding stock, should not simply look for a dog or bitch with normal hips, but should try and select stock from families that produce good hips (more than 75% normal hips). If the parents, grandparents and siblings of a dog all have normal hips, statistically the chances of that dog also producing normal hips are of course much better than those of a dog with A1-A1 hips but with parents or many family members with affected hips.

SEVERE HIP DYSPLASIA

Unfortunately so few owners are prepared to x-ray their Boxers in this country that it is quite difficult to discover whether there are families with good hips in addition to all the other traits we look for when selecting breeding partners.
There are several reasons why Boxers are not generally x-rayed:

VERY SEVERE HIP DYSPLASIA

Because of their strong musculature, young Boxers with D1-D1 or even E1-E1 hips may very seldom or only intermittently show clinical signs of the disease. In addition, breeds - such as the Boxer - that were originally developed for “blood sports” (e g bull baiting and dog fighting) are genetically programmed not to show pain. A dog in pain is vulnerable and a vulnerable dog was a dead dog. Boxers may therefore be in pain without their owners realising it. They simply assume that their dogs must have normal hips because they do not show clinical signs of dysplasia and do not see why the dog should be x-rayed.

When such a dog gets older, it will however almost certainly suffer chronic pain, because the osteoarthritis in dysplastic hips gets progressively worse as the dog ages. Other owners may be afraid of discovering that their Boxers do not have good hip joints and prefer the “ostrich” approach of breeding regardless – ignorance, after all, is bliss!
For me there are two main reasons to select and breed for good hips: I want my Boxers to be able to jump and compete in working trials without breaking down or developing arthritis and above all I would rather not be responsible for breeding Boxers condemned to years of chronic suffering and pain when they grow old.

- Marlien Heystek