Canine Hip Displasia

Hip rads
Canine hip dysplasia (CHD) is a developmental trait primarily affecting medium and large breed dogs but it is also known
in Cardigan Welsh Corgis. Many Cardis who are diagnosed with affected hips however do not seem to suffer a lot from
this defect and manage to live their life to the max.
CHD is characterized by faulty conformation and laxity of the hip joint that usually affects both hips. It can be detected
radiographically as subluxation of the affected hip. The eccentric load on the articular surface of the femoral head (ball)
and acetabulum (socket or cup) leads to erosion of the cartilage, inflammation in the joint, and debilitating pain. Clinically,
the osteoarthritis or degenerative joint disease that results from hip dysplasia is characterized by hind limb lameness,
reduced exercise tolerance, reluctance to jump, and poor hind limb muscle mass.
There are several methods for scoring CHD. In The Netherlands the x-rays are rated by a panel of three expert evaluators
assigned for this task by the Dutch Kennelclub, this  department is known as GGW (Health, Behaviour and Wellbeing).
Cardis can be evaluated from the age of 12 months. In the Netherlands we get an evaluation based on FCI regulations.
Because of this it should be possible to compare the scores between the different countries. Today we still see different
scores in our breed in certain FCI countries, it raises the question whether the hips of these dogs are of less quality or if
there is a different method of scoring within the FCI countries.
Then there is the Orthopedic Foundation for Animals that scores hips. Many Cardigan hips have been evaluated by the
OFA and many results can be found in the OFA’s database.
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 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.
Excellent Hips Good Hips
Excellent: this classification is assigned for superior conformation in comparison to other animals of the same age and
breed. There is a deep seated ball (femoral head) which fits tightly into a well-formed socket (acetabulum) with minimal
joint space. There is almost complete coverage of the socket over the ball.
Good: slightly less than superior but a well-formed congruent hip joint is visualized. The ball fits well into the socket and
good coverage is present.
Fair Hips Mild Dysplasia
Fair: Assigned where minor irregularities in the hip joint exist. The hip joint is wider than a good hip phenotype. This is
due to the ball slightly slipping out of the socket causing a minor degree of joint incongruency. There may also be slight
inward deviation of the weight-bearing surface of the socket (dorsal acetabular rim) causing the socket to appear slightly
shallow. This can be a normal finding in some breeds however, such as the Chinese Shar Pei, Chow Chow, and Poodle.
Borderline: there is no clear cut consensus between the radiologists to place the hip into a given category of normal or
dysplastic. There is usually more incongruency present than what occurs in the minor amount found in a fair but there are
no arthritic changes present that definitively diagnose the hip joint being dysplastic. There also may be a bony projection
present on any of the areas of the hip anatomy illustrated above that can not accurately be assessed as being an
abnormal arthritic change or as a normal anatomic variant for that individual dog. To increase the accuracy of a correct
diagnosis, it is recommended to repeat the radiographs at a later date (usually 6 months). This allows the radiologist to
compare the initial film with the most recent film over a given time period and assess for progressive arthritic changes
that would be expected if the dog was truly dysplastic. Most dogs with this grade (over 50%) show no change in hip
conformation over time and receive a normal hip rating; usually a fair hip phenotype.
Mild Hip Dysplasia: there is significant subluxation present where the ball is partially out of the socket causing an
incongruent increased joint space. The socket is usually shallow only partially covering the ball. There are usually no
arthritic changes present with this classification and if the dog is young (24 to 30 months of age), there is an option to
resubmit an radiograph when the dog is older so it can be reevaluated a second time. Most dogs will remain dysplastic
showing progression of the disease with early arthritic changes. Since HD is a chronic, progressive disease, the older the
dog, the more accurate the diagnosis of HD (or lack of HD).
Moderate Dysplasia Severe Dysplasia
Moderate Hip Dysplasia: there is significant subluxation present where the ball is barely seated into a shallow socket
causing joint incongruency. There are secondary arthritic bone changes usually along the femoral neck and head (termed
remodeling), acetabular rim changes (termed osteophytes or bone spurs) and various degrees of trabecular bone pattern
changes called sclerosis. Once arthritis is reported, there is only continued progression of arthritis over time.
Severe Hip Dysplasia: assigned where radiographic evidence of marked dysplasia exists. There is significant
subluxation present where the ball is partly or completely out of a shallow socket. Like moderate HD, there are also large
amounts of secondary arthritic bone changes along the femoral neck and head, acetabular rim changes and large
amounts of abnormal bone pattern changes.
Here is a table that shows the different scoring methods.


FCI (European)

BVA (UK/Australia)

SV (Germany)



0-4 (no > 3/hip)




5-10 (no > 6/hip)









Fast Normal




Noch Zugelassen










Then there is the PennHIP method. To go short: The PennHIP method is a novel way to assess, measure and interpret
hip loint laxity. It consists of three separate radiographs: the distraction view, the compression view and the
hip-extended view. The distraction view and compression view are used to obtain accurate and precise measurements
of joint laxity and congruity.
The hip-extended view is used to obtain supplementary information regarding the existence of osteoarthritis
(OA) of the hip joint. (The hip-extended view is the conventional radiographic view used to evaluate the integrity of the
canine hip joint.) The PennHIP technique is said to be more accurate than the current standard, and it has been shown
to be a better predictor for the onset of OA.
The radiographs pictured here are of the same dog, yet the hip joint laxties in each view look very different. Notice that
the hips in the distraction view appear to be much looser than they do in the hip-extended view.

Distraction View

Compression View

Hip-Extended View

The obvious contrast in joint laxity between the distraction and hip-extended views demonstrates
the fundamental difference between the two radiographs. The looser the joint on the distraction

view, the greater is the chance that the hip will develop OA. The hip-extended view tends to

mask true hip joint laxity because the joint capsule is wound up into a tightened orientation when

the hips are extended. This explains why measurable joint laxity on the distraction view is always

greater than the measurable laxity from the hip-extended view. In fact, distraction laxity is up to 11

times greater depending on the breed of dog under study.

The compression view is used to determine the "goodness of fit" of the femoral heads into the

acetabula. In a hip with OA, the remodeling that occurs in the acetabulum and/or the femoral head,

will often result in an ill-fitting "ball" and "socket".


To summarize, PennHIP method:


Obtains OA readings from the standard hip-extended view


Obtains hip joint congruity readings from the compression view


Obtains quantitative measurements of hip joint laxity from the distraction view

CHD in dogs is an inherited, polygenic trait in which mutations in several genes called quantitative trait loci (QTLs)
contribute to its clinical expression. Many dogs with normal hips on radiographs carry at least a modicum of the trait-
causing mutations but not all that are necessary to cause physical expression of the trait. CHD is a quantitative or
complex trait that is expressed as a continuum from imperceptible to severe forms. This continuum of trait expression is
due to environmental influences (such as plane of nutrition and exercise, as well as other unknown factors) which
interact with the genetic constitution to affect the degree to which the trait is manifested.
CHD has a heritability between 0.20-0.7. This means that between 20 and 70% of the physical appearance of the hips
of each dog in a pedigree can be attributed to its genetic relationships within the pedigree.
It will take a concerted effort to rid breeds of the genetic mutations that cause CHD or conversely, to introduce
 protective alleles at the loci that cause good hips. Selective breeding based on current radiographic methods can
reduce the frequency of CHD in a population.  Breeding two dysplastic dogs can yield a 75% incidence of hip
dysplasia in offspring, while mating two unaffected dogs can yield a 25% incidence of the disease. Selective
breeding using normal dogs from normal parents and grandparents, as well as progeny testing, should decrease the
incidence of CHD.
Until there is a genetic test for CHD, so we can detect genetically susceptible dogs, the best indication of a dog's
genetic makeup is where it came from (its' parents and grandparents), what it produces (its' offspring), and the
phenotype of its' siblings or half sibs. Dogs with normal hip radiographs that carry some of the mutations that cause
CHD but perhaps not the major ones, when bred to a mate that also carries some of the mutations for CHD, may
produce affected offspring.
To test whether a dog carries some of the mutations (even if the dog has OFA-good hips), it should be bred to sires
or dams with good hips and the proportion of affected offspring recorded (progeny testing). As many as 15-20
offspring should be produced to be reasonably sure that the parents do not carry important mutations. This is an
unreasonable burden for dog breeders to bear. Breeders should attempt to breed dogs with the best hips in
 their colony as well as to dogs with the other optimal breed characteristics and temperament.
At the Cornell University Hospital for Animals in New York they have been searching for the genes that contribute
to hip dysplasia. When an owner comes to this hospital for hip radiographs, they are asked to donate a small 
sample of blood from their dog for DNA isolation. This DNA and the hip radiograph measurements are then used
later to discover and confirm the mutations that contribute to hip dysplasia. Once they know which genes and
biochemical pathways lead to good and poor hip conformation, they can develop novel treatments which can be
applied at an early age.