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.
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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
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