In the battle against canine hip dysplasia, identification,
research, and careful breeding selection are the
weapons of choice.
by Jerold S Bell, DVM, Tufts
University School of Veterinary Medicine
For affected dogs, hip
dysplasia can be a debilitating and painful disease. It has
been one of the fancy’s great challenges to combat and treat
this hereditary developmental disorder, whose signs can
include hip-joint pain, hind-limb weakness, lameness,
exercise intolerance, degenerative joint disease, and
arthritis. The disorder can include several abnormalities of
the hip joints, such as joint laxity, anatomical
abnormalities, and a predisposition to arthritis. While hip
dysplasia is commonly perceived to be a disorder of larger
dogs, it also occurs in small breeds, mixed-breed dogs, and
even cats. The Pug, for example, has a significant frequency
of affected dogs, while the Siberian Husky has a relatively
low frequency of dysplasia.
Most experts agree that the
majority of dogs that develop hip dysplasia have outwardly
normal hips when they are very young, and develop the
anatomical or laxity changes associated with the disorder
during the first year or two of life. Initial symptoms may
appear from 4 months to 1 year of age, and include joint
pain, a swaying and unsteady gait, “bunny hopping”,
difficulty rising from a sitting position, difficulty with
stair-climbing, and an aggravation of these signs with
are several methods used to diagnose hip dysplasia. The
standard procedure is the extended-leg (x-ray). This is a
radiograph of the pelvis and hip joints taken with the dog
on its back, with hind legs extended. This hip-evaluation
method is the one used by the Orthopedic Foundation for
Animals (OFA), as well as by most European and Canadian
The hip is a ball (femoral
head) and socket (acetabulum) joint. The OFA evaluates the
hip radiograph for nine anatomical aspects. These include; a
round femoral head, a deep acetabulum, a prominent notch in
the femoral neck, a straight up-and-down cranial rim of the
acetabulum, and minimal joint laxity. Good hip conformation
is determined by imagining a line (dashed line in the
drawing) connecting the outer edges of the acetabulum, and
observing at least half of the femoral head enclosed within
the acetabulum. Bony remodeling and arthritic changes will
fill in the notch at the femoral neck, and cause “lipping” -
proliferation of bone at the cranial acetabular rim.
will certify a dog’s hips (at 2 years of age or older) as
excellent, good, fair, or borderline, or as mildly,
moderately or severely dysplastic.
The British Veterinary
Association/Kennel Club (BVA/KC) evaluates the same
extended-leg radiograph at 1 year of age or older. Unlike
OFA’s rating system, it separately scores the nine
anatomical aspects of the pelvic radiograph for each hip.
The nine scores are added up for each hip, then totaled for
the dog’s final rating. A perfect rating would be zero; the
worst would be 106 (53 for each hip).
Pennsylvania Hip Improvement Program (PennHIP) method of
evaluating the hip joint is based on laxity alone. This
method utilizes two separate radiographs on an anesthetized
dog to record the hips in compressed and distracted views.
The distracted-view radiograph (to the right) is taken while
applying a uniform force on the hips to measure the maximum
distractibility of the hip joints. (Distractability is the
distance that the soft tissue allows the head of the femur
to come out of the acetabulum.) The measured difference
between the compressed and distracted views is used to
compute a distraction index (DI). A DI of zero indicates no
laxity of the hips, and a DI of 1.0 indicates luxation of
the hips. Dogs with a DI of under 0.3 almost always have
normal hips, and those over 0.7 are almost always dysplastic.
PennHIP was designed to create a selection tool for tighter
hips. By computing a breed average of distractibility, and
selecting for tighter hips than the breed average, it is
believed that the incidence of hip dysplasia should decrease
Fighting Back With
Hip dysplasia is considered a moderately inherited disorder,
with researchers computing heritability values of 28 to 40
percent. This means that 28 to 40 percent of the variation
between affected and unaffected relatives is due to genes.
While it is more difficult to manage disorders with this
level of heritability, many traits in this range improve
with proper selection.
hip dysplasia is a polygenic disorder controlled by several
gene pairs, the disease affects individual dogs due to
different genetic combinations. The two dogs in the
radiographs to the left have severe hip dysplasia. The one
at the top has severe laxity, while the other (bottom) has
tight hips, but with shallow acetabula and severe bony
changes. Both these dogs have hip dysplasia, but due to
different genetic causes.
One reason selection offers
limited results is that many breeders are selecting dogs
based solely on their OFA hip rating, and not on the
specific aspects of the hip radiograph. If a dog receives a
fair hip-rating due to some shallowness in it’s acetabula,
it should be bred to a dog with deep acetabula (in addition
to considering all other factors if it is going to be bred).
If a dog’s hips have demonstrable laxity, then it should be
bred to a dog with tight hips.
The BVA/KC’s dysplasia
rating allows breeders to identify precisely how their dog’s
hip-rating points are calculated. With this system it is
easier to select prospective mates that will correct and
compliment the different elements of hip joint conformation.
With the OFA system, it is up to the individual breeder to
work with their veterinarian to break down the hip
radiograph into these separate components. By selecting for
individual components of the hip radiograph, you may be more
directly selecting for specific “normal-hip” genes.
most important factor in selecting against a polygenic
disorder like hip dysplasia is to seek breadth of pedigree.
Most breeders select normal parents with normal
grandparents, and expect to produce all normal offspring.
This is selection based on depth of pedigree. With polygenic
traits, the hip status of breeding dogs’ siblings better
represents the range of genes that can be present. With
breadth of normalcy in the littermates of breeding dogs, and
even of parents of breeding dogs, you are more efficiently
selecting for a preponderance of those “normal-hip” genes.
To help control the
disorder, the OFA has a longstanding hip dysplasia registry.
Until recently, results were available only for dogs with
normal-hip certification. The OFA has now moved to a
semi-open registry, which allows owners the option of having
their dogs’ hip status posted on the OFA website (www.offa.org),
regardless of a normal or affected certification. The
Institute for Genetic Disease Control (GDC) hip registry was
developed with the open-registry concept, and, as of summer
2002, will be merged into the OFA database. Through the
OFA’s online searchable registry, you can find the hip
status of littermates and relatives to determine normality
in the pedigree breadth. Both the OFA and PennHIP
radiographic methods can report low levels of false positive
and false negative predictions for future dysplastic
development. The OFA radiograph documents anatomical
abnormalities (shallow sockets, early bony-changes), but
only natural laxity in a hip-extended view. The PennHIP
radiograph documents maximum distractibility, but there are
dogs with DIs between 0.3 and 0.7 that can end up being
clinically normal or affected. For both methods,
radiographic findings at an early age are highly correlated
to dysplasia at a later age. OFA offers preliminary
evaluations at any age, but does not give permanent
certification until two years of age, when over 95 percent
of affected dogs will show radiographic signs.
One significant factor in the development of hip dysplasia
is the nutritional load, especially in growing large-breed
dogs. Feeding high-calorie puppy food promotes rapid bone
growth and weight gain. The soft-tissue components of the
hips don’t mature and grow at the same rate as the bones.
Often, by the time these soft-tissue components catch up,
there can be bony deformity, due to a period of unstable hip
joints. By switching to the lower-calorie large-breed puppy
growth food, or switching to adult dog food after fourteen
weeks of age, the growth rate can be slowed, and all of the
components of the hip joints can mature in unison. The adult
size of the dog is genetically determined, and
reduced-calorie feeding will only alter the age when this
size is attained.
Excessive jumping and
compaction activity on the hip joints during the critical
growth periods prior to skeletal maturation can also affect
the degree of later dysplastic development in genetically
predisposed dogs. Changing feeding protocols and managing
excessive environmental stress will probably not prevent hip
dysplasia in genetically predisposed dogs, just as
reasonable over-nutrition and activity will probably not
cause hip dysplasia in genetically normal dogs. However,
modifying feeding practices can alter the degree or severity
of clinical signs in affected dogs. Breeders should evaluate
prospective breeding dogs that have been raised under fairly
uniform conditions, so that any differences between them are
due to heredity, not environmental influences.
There are no scientifically
proven drugs, vitamins, or food supplements that will
protect the hips of genetically predisposed dogs from
developing hip dysplasia. Joint-formula compounds (including
glucosamine and chondroitin) are shown to diminish hip-joint
pain in dogs. Nonsteroidal anti-inflammatory drugs (such as
aspirin, Rimadyl, and Etogesic) are also effective for
treating joint pain. Owners should discuss with their
veterinarian which medications are appropriate for their
dog’s condition. Avoiding overfeeding, and maintaining a
lean body weight will also diminish hip pain in affected
There are two types of
early-intervention surgery that attempt to prevent the
progression of hip dysplasia in young dogs. These are
designed to improve the integrity of the hip joints when
there are shallow hip sockets or significant joint-laxity.
They both act to rotate the acetabulum upward and outward,
so it has greater coverage and support for the head of the
femur. With a triple pelvic osteotomy (TPO), three cuts are
made in the pelvis with a bone saw to isolate the hip
socket. It is then rotated and reattached with metal plates.
This surgery must be performed before any arthritic changes
The other surgery is an
experimental procedure called a juvenile pubic
symphysiodesis (JPS). An electro-scalpel is used to close
the growth plate on the floor of the pelvis. With normal
growth occurring in the rest of the pelvis, the hip sockets
then rotate outward. This procedure must be performed on
dogs between 12 and 20 weeks of age, before significant
pelvic growth has occurred. The affect of the procedure
beyond 2 years of age has not been studied.
Both the TPO and JPS
require the early identification of candidates for surgery,
before the bony changes of hip dysplasia occur. This creates
a problem, as there is no accepted diagnostic test designed
to predict with high certainty which dogs will develop
debilitating hip dysplasia that will require surgery.
Several surgeons recommend early intervention surgery based
on a PennHIP measurement of laxity in young dogs. Dr. Gail
Smith, professor of orthopedic surgery at the University of
Pennsylvania School of Veterinary Medicine, believes that
this is a misuse of the technique. “PennHIP was designed as
a selection tool to quantify a probability or risk factor
for developing later hip dysplasia,” says Smith, who
developed the PennHIP method. “The technique wasn’t designed
as an indicator for surgery.” He feels that a dog being
considered for any type of hip dysplasia surgery should be
demonstrating some clinical symptom of the condition.
The TPO procedure has a
longer track record to measure its outcome in older dogs.
While research shows that in many cases the procedure does
not stop the radiographic progression of hip dysplasia or
arthritis, dogs who have undergone the surgery appear to
experience less discomfort. However, since studies have
shown that 76 percent of all dogs with radiographic signs of
hip arthritis do well without surgery, controlled studies
still need to be undertaken to determine the true value of
these early intervention surgeries.
There are two accepted
surgical procedures for removing the pain and lameness
caused by hip dysplasia: femoral head and neck excision, and
total hip replacement. Both of these surgeries are
considered salvage procedures, as they remove the arthritic
bone-on-bone contact of the hip joint, thus relieving the
pain associated with it.
A femoral head and neck
excision removes the ball from the ball-and-socket joint,
and uses the muscles of the pelvis to support the hind leg.
This procedure works well in most dogs up to 50 pounds,
though heavier dogs could also be helped. It requires good
muscle strength in the leg and buttocks since these, rather
than bone, provide the support.
Total hip replacement,
while the more aggressive surgery, works very well on
affected dogs. The head of the femur is replaced with a
metal implant, and the acetabulum is replaced with a
synthetic plastic implant. With updated materials and
techniques, dogs receiving total hip replacement have few
complications, and return to normal function without pain.
Any dog whose condition is severe enough to require surgery
should be spayed or neutered at the same time.
In addition to the exploration into techniques to identify
and treat dogs with hip dysplasia, research is being
conducted to find the genetic causes of the condition. Dr.
George Brewer, of the University of Michigan Medical School,
is conducting research to find genes that cause canine hip
dysplasia. Using 12 breeds, he is investigating candidate
genes that code for hip-related functions such as physiology
and connective tissue. “We are hoping to find one or two
major trigger genes for hip dysplasia in each breed,” says
Brewer, whose research is supported by a grant from the AKC
Canine Health Foundation.
At the Cornell University
College of Veterinary Medicine, Dr. Rory Todhunter is
attempting – in a different way - to identify genes that
cause hip dysplasia. He bred normal Greyhounds to dysplastic
Labrador Retrievers, and then bred their offspring back to
either normal Greyhounds or dysplastic Labrador Retrievers.
Through manipulating the genes in this breeding scheme, he
is trying to identify hip dysplasia-causing genes in the
normal and dysplastic crossbred offspring. The goal of both
of these research efforts is to develop genetic tests that
can be used to select for genetically normal breeding-dogs.
Canine hip dysplasia
continues to be a serious disorder across breed lines. As
breeders and owners learn the proper techniques to decrease
the frequency of producing affected dogs, we can anticipate
significant progress in the reduction of this damaging and
Hip Dysplasia by
Breed (OFA Statistics):
AKC Breeds Most
Clumber Spaniel 49.6%
Neopolitan Mastiff 47.6%
St. Bernard 47.0%
Sussex Spaniel 41.2%
Bassett Hound 28.6%
AKC Breeds Least
Australian Terrier 0.0%
Siberian Husky 2.1%
Ibizan Hound 2.2%
Canaan Dog 2.4%
Pharoah Hound 2.7%
Belgian Sheepdog 2.9%
First printed in the July 2002 issue of the
Reproduced here by permission of the author; all rights reserved.