Hip joint of dog dysplasia is a disease manifested by abnormal forming of hip
socket and head of femur, they are incongruent (hip sockets are of a different
shape than head of femur) and therefore joint is ubstable. Head of femur fit
in the socket very tight in a healthy joint. If displasia occurs, a junction
is more free, head of femur partialy loosen from socket (subluxate). As a result
of joint detachment degenerative joint disease (arthrosis) is developed in an
advanced stage of HD. HD afflicts mostly big and giant breeds but generally
can afflict every breed. HD is not a congenital disease and is manifested during
growth. But there is a heredital predisposition. Development of HD depends on
individual genes ( the shape of joint structures the amount of muscle mass)
and environmental factors ( the speed of growth, feeding, everyday load). US
passive laxity (i.e. HD predisposition) research revealed that heritability
at German shepherd is 0,74 and at Labrador retriever even 0,92. The passive
laxity was detected by usin Penn HIP system of hip joint examination. This system
is used in the USA for the examination of even 16 week old pupies. Another works
revealed that HD negative parents have 64-81% negative offsprings and 19-37%
HD positive offsprings. Contrary the rate of offsprings of HD positive parents
was 17-37% HD negative and 63-93% HD positive.
All dogs without exception are born with healthy hip joints, even those suffering
from HD lately. Most important time of development of hip bone are first two
months when joint pasts are still soft and consist mainly of cartilage. Cartilage
is lately replaced by bone mass in the course of ossification. The instability
of joint develops, if strenghts impact on cartilage exceed its elastic limit.
Under normal conditions strengths impact the surface of joint cartilage almost
perpendicular approximately to its centre. Under the load the head of instable
joint is forced more to the front outside rim of joint and not to the centre
as in healthy joint. As a consequence of overloading of upper joint rim and
socket develops more flat and its development is slowed. The socket becomes
more and more flat and a head of femur is slowly released. And again, more pressure
is loaded to front upper rim, it becomes more and more flat and head is more
and more loosen. At the end of this circle, we can see HD of various degree.
If more than half of head is out of the socket, then it is called subluxation.
Subluxation can continue into luxation, when head is totaly out of socket. The
head loose its regular shape because pressure from socket is irregular.
If head of femur and socket are of the different shape or joint is weaken,
then pressure to cartilage is unequal. This leads to itīs degeneration. The
cartilage becomes more harsh fibrous and gradual destruction occurs. In reaction
to cartilage shrinkage bone becomes wider and thicker. X-ray can determine subchondral
sclerosis in the overloaded area. On the edge of the joint bone protrusions-osteophytes
exostoses are developed. These protrudings can be found on the ligament anchorages
between the head neck of femur. If these protrudings are seriously developed,
they change the shape of head from spherical to more mushroom form. All these
secondar artritic changes are manifestations of degenerative joint process called
osteoarthrosis - in case of hip joint coxarthrosis. the result of them is a
joint deformation.
The most accurate HD diagnostic method is X-ray. For eliable judgement a quality
X-ray snap is necessary. To prevent the confusion the snap must be safe labeled.
The snap is sent to veterinarian approved for HD diagnostic for the particular
breed. The minimal age for valid judgement is 12 months in Czech Republic, the
minimal age for big and giant breeds is 18 months. The minimal age of any particular
breed is determined by breed clubs.
The HD negative judgement should not be assessed before the age of two. FCI
determines the minimal age 12 months and 18 months for DH. American OFA have
changed the minimal age from 12 months to 24 months, because they discovered
that not all cases of HD can be found at the age of 12 months. Several works
of different authors determined, that X-ray method made at the age of 12 months
can reveal only 66% of HD positive dogs whereas 18 months can reveal 84% HD
positive dogs. At the age of 24 months 94% positive dogs can be revealed.
For X-ray diagnosis ventrolateral projection snap is used i.e. a dog lies on
back hindlegs extended evenly backwards. A good position is made on the V shaped
table. Good myorelaxation is made by narcotics. The snap must include pelvis,
sacrum and humer including knee joint. For correct judgement the snap must be
symetric (bad projection can cause bad judgement). X-ray diagnostic is based
on judgement of degree of subluxation and presence of secundar arthrotic chages.
The degree of subluxation is made on the base of shape and width of joint cleft
position of the centre of head of humerus to upper rim of socket and of the
Norberg-Olssonīs angle.
On the base of these criteria FCI scientic commision adopted classification
chart that divides HD affection into five degrees. FCI chart amended in 1993
denominate particular degrees by leters A-E. Apart from this chart, several
other chart does exist all over the world. It is US OFA chart, British and Swiss
mark system and Swedish HD chart.
In Czech Republic adapted FCI chart is used. Degree of joint affection is expressed
by numbers 0-4, where 0 is HD negative, 1 is borderline between negative and
HD, 2 is mild HD, 3 is intermediate and 4 is severe HD. Clinical symptoms HD
as getting up with problems unwilling to move and limping that becomes worse
after load should not always agree with X-ray.
HD is heredital disease conditioned by interaction of more genes. There is
also an important role of environment. For its difficult genetic base, it is
impossible to eradicate it despite breeders effort. But consistent breeding
effort can substantially lowered its incidence.
MVDr. Jan Sterc, MVDr. EVA Stercova
Scheme of X-ray picture in ventrolateral projection
Ventrolateral X-ray snap of normal hip joint
Gleft is narrow, surface is congruent. Head of humer is idealy
half bulbous, socket is deep more than half of head is in socket.
A - Joint socket
B - Front rim of socket
C - Front and lateral rim of socket
D - Upper rim of socket
E - Caudal rim of socket
HD joint
Cleft rim is wider joint surfaces are not of the same shape,
the centre of head is outside the upper rim of socket, frontal margin of socket
becomes more flat and sclerosis of subchondral bone can be seen.
HD joint with arthrosis symptoms
A - osteophtys on front lateral rim of socket
B - abrasion of front lateral rim
C - wider "forked" joint cleft
D - osteophtys on the base of socket
E - "collar" of osteophtys in the area of head and neck
F - osteophtys along the upper edge of neck
HD joint with degenerative mutations
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