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The Dysplastic
Joint
Hip Dysplasia is a
terrible genetic disease because of the various
degrees of arthritis (also called degenerative
joint disease, arthrosis, osteoarthrosis) it can
eventually produce, leading to pain and
debilitation.
The very first
step in the development of arthritis is articular
cartilage (the type of cartilage lining the joint)
damage due to the inherited bad biomechanics of an
abnormally developed hip joint. Traumatic
articular fracture through the joint surface is
another way cartilage is damaged. With cartilage
damage, lots of degradative enzymes are released
into the joint. These enzymes degrade and decrease
the synthesis of important constituent molecules
that form hyaline cartilage called proteoglycans.
This causes the cartilage to lose its thickness
and elasticity, which are important in absorbing
mechanical loads placed across the joint during
movement. Eventually, more debris and enzymes
spill into the joint fluid and destroy molecules
called glycosaminoglycan and hyaluronate which are
important precursors that form the cartilage
proteoglycans. The joint's lubrication and ability
to block inflammatory cells are lost and the
debris-tainted joint fluid loses its ability to
properly nourish the cartilage through impairment
of nutrient-waste exchange across the joint
cartilage cells. The damage then spreads to the
synovial membrane lining the joint capsule and
more degradative enzymes and inflammatory cells
stream into the joint. Full thickness loss of
cartilage allows the synovial fluid to contact
nerve endings in the subchondral bone, resulting
in pain. In an attempt to stabilize the joint to
decrease the pain, the animal's body produces new
bone at the edges of the joint surface, joint
capsule, ligament and muscle attachments (bone
spurs). The joint capsule also eventually thickens
and the joint's range of motion decreases.
No one can predict
when or even if a dysplastic dog will start
showing clinical signs of lameness due to pain.
There are multiple environmental factors such as
caloric intake, level of exercise, and weather
that can affect the severity of clinical signs and
phenotypic expression (radiographic changes).
There is no rhyme or reason to the severity of
radiographic changes correlated with the clinical
findings. There are a number of dysplastic dogs
with severe arthritis that run, jump, and play as
if nothing is wrong and some dogs with barely any
arthritic radiographic changes that are severely
lame.
Hip
Dysplasia Radiograph Procedures
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Radiographs
submitted to the OFA must follow the American
Veterinary Medical Association guidelines for
positioning. This view is accepted world wide
for detection and assessment of hip joint
irregularities and secondary arthritic hip
joint changes. To obtain this view, the animal
must be placed on its back in dorsal
recumbency with the rear limbs extended and
parallel to each other. The knees (stifles)
are rotated internally and the pelvis is
symmetric. Chemical restraint (anesthesia) to
the point of relaxation is recommended. For
elbows, the animal is placed on its side and
the respective elbow is placed in an extreme
flexed position.
The radiograph
film must be permanently identified with the
animal's registration number or name, date the
radiograph was taken, and the veterinarian's
name or hospital name. If this required
information is illegible or missing, the OFA
cannot accept the film for registration
purposes. The owner should complete and sign
the OFA application. It is important to record
on the OFA application the animal's tattoo or
microchip number in order for the OFA to
submit results to the AKC. Sire and dam
information should also be present.
Radiography of
pregnant or estrus females should be avoided
due to possible increased joint laxity (subluxation)
from hormonal variations. OFA recommends
radiographs be taken one month after weaning
pups and one month before or after a heat
cycle. Physical inactivity because of illness,
weather, or the owner's management practices
may also result in some degree of joint
laxity. The OFA recommends evaluation when the
dog is in good physical condition.
Chemical
restraint (anesthesia) is not required by OFA
but chemical restraint to the point of muscle
relaxation is recommended. With chemical
restraint optimum patient positioning is
easier with minimal repeat radiographs (less
radiation exposure) and a truer representation
of the hip status is obtained.
For large and
giant breed dogs, 14" x 17" film size is
recommended. Small film sizes can be used for
smaller breeds if the area between the sacrum
and the stifles can be included.
If a copy is
necessary ask your veterinarian to insert 2
films in the cassette prior to making the
exposure. This will require about a 15%
increase in the kVp to make an exact duplicate
of the radiograph sent to OFA. Films may be
returned if a $5.00 fee and request for return
are both included at time of submission.
Good contrast
is desirable (high mAs, low kVp). Grid
techniques are recommended for all large dogs. |
Hip
Grades
The
phenotypic evaluation of hips done by the
Orthopedic Foundation for Animals falls into seven
different categories. Those categories are normal
(Excellent, Good,
Fair),
Borderline, and dysplastic (Mild,
Moderate,
Severe). Once each of the
radiologists classifies the hip into one of the 7
phenotypes above, the final hip grade is decided
by a consensus of the 3 independent outside
evaluations. Examples would be:
- Two
radiologists reported excellent, one good—the
final grade would be excellent
- One
radiologist reported excellent, one good, one
fair—the final grade would be good
- One
radiologist reported fair, two radiologists
reported mild—the final grade would be mild
The hip grades of
excellent, good and fair are within normal limits
and are given OFA numbers. This information is
accepted by AKC on dogs with permanent
identification (tattoo, microchip) and is in the
public domain. Radiographs of borderline, mild,
moderate and severely dysplastic hip grades are
reviewed by the OFA radiologist and a radiographic
report is generated documenting the abnormal
radiographic findings. Unless the owner has chosen
the open database, dysplastic hip grades are not
in the public domain.
Preliminary Evaluations
for
animals under 24 months
Frequently, breeders want early knowledge of the
hip status on puppies in a given litter.
Preliminary hip evaluations may be as valuable to
the owner or breeder as the final OFA evaluation.
This allows early selection of dogs for use as
show/performance/breeding prospects and dogs best
suited for pet homes.
The OFA accepts
preliminary consultation radiographs on puppies as
young as 4 months of age for evaluation of hip
conformation. If the dog is found to be dysplastic
at an early age, the economic loss from the cost
of training, handling, showing and so forth can be
minimized and the emotional loss reduced. These
preliminary radiographs are read by the OFA
veterinary radiologists and are not sent to
outside radiologists. The same hip grades are
given to preliminary cases.
A recent
publication* compared the reliability of the
preliminary evaluation hip grade phenotype with
the 2 year old evaluation in dogs and there was
100% reliability for a preliminary grade of
excellent being normal at 2 years of age
(excellent, good, or fair). There was 97.9%
reliability for a preliminary grade of good being
normal at 2 years of age, and 76.9% reliability
for a preliminary grade of fair being normal at 2
years of age. Reliability of preliminary
evaluations increased as age at the time of
preliminary evaluation increased, regardless of
whether dogs received a preliminary evaluation of
normal hip conformation or HD. For normal hip
conformations, the reliability was 89.6% at 3-6
months, 93.8% at 7-12 months, and 95.2% at 13-18
months. These results suggest that preliminary
evaluations of hip joint status in dogs are
generally reliable. However, dogs that receive a
preliminary evaluation of fair or mild hip joint
conformation should be reevaluated at an older age
(24 months).
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