| Hip Information |
To begin I must state that I am a firm believer in xraying the hips of all dogs being considered for breeding purposes.
Through this article, I would like to dispel myths and enlighten you regarding the FACTS on hip xrays.
Over the past two years, I have read study after study and done a great deal of research covering the topics of OFA,
PennHip and Hip Positioning. I DO NOT believe either OFA or PennHip to be more superior than the other, but BOTH
useful tools in determining the status of the canine hip.
The information here was compiled referencing the people listed at the bottom of the page.
OFA (Orthopedic Foundation for Animals)
http://www.offa.org
Procedure - The dog is placed on its back. The hind legs are extended fully in a caudal (away from the rear end)
direction, held parallel and rotated fully in a medial direction. When this position has been achieved, the cranial(top)
mid line of the femora(plural for femur-thigh bone) will face up directly toward the xray machine. Sedation may be
required to achieve this position in all but the most cooperative dogs. OFA does recommend sedation, but does not
require it. Always remember this positioning is NOT normal for the canine hip and if the animal is not sedated can be
extremely uncomfortable.
OFA offers preliminary hip dysplasia(HD) screening on dogs as young as 4 months old, but will not CERTIFY a dogs
hip status until 24 months of age. The reasoning behind this is that the animal has not finished growing. Since true
HD (abnormal development or an abnormal structure resulting from such growth) is usually evident within the first year
of a dogs life, an OFA Preliminary evaluation is an excellent tool for assessing breeding stock early. HD is the primary
cause of DJD(Degenerative Joint Disease - a debilitating disease that breaks down the cartilage and remodels the
bones of the hip), but not the only cause of DJD. For example: A canine athlete may show minimal signs of DJD
without ever having HD in the same way a human athlete will. If your dog is a canine athlete: protection sport, field
work, agility or even SAR(search and rescue) you should send a letter in with you're dog's xray stating what arena(s)
the dog is active and for how long the dog has been doing it. The evaluating veterinarians will take that information
into consideration when reviewing the xrays.
There are seven levels of HD as diagnosed by OFA:
EXCELLENT - Superior hip joint conformation(tight joint space and almost complete coverage of the femoral head) as
compared to other dogs of the same breed and age.
GOOD - Well formed hip conformation, most of the socket covers the femoral head but there is congruent(even) joint
space.
FAIR - a) There is congruent joint space, but the socket's weight bearing surface is deviated inward
b) The joint space is slightly incongruent, but still with good femoral head coverage.
BORDERLINE - There is no clear cut evidence for the evaluating veterinarians to put the hips in either normal or
dysplastic category and re-xray and submission is suggested in 6 months.
MILD - There is significant sub luxation present where the ball is partially out of the socket causing incongruent joint
space and the socket is shallow. There are usually no arthritic changes in dogs 24-30 months. Re-submission is
suggested as the dog ages.
MODERATE - There is substantial sub luxation of the ball from the joint where the ball barely fits into the joint
anymore. There are secondary arthritic changes along the femoral head, neck and acetabular rim(socket edge).
SEVERE - There is significant sub luxation present where the ball is either partially or completely out of a shallow
socket and always large amounts of arthritic changes to the whole joint area.
OFA is a subjective test where two to three vets look at the xrays and give there "opinion" of the hip status. For
example: 2 vets say FAIR, 1 vet says GOOD..the dog scores a FAIR. One says EXCELLENT, one says FAIR, one
says GOOD... the dog scores a GOOD and so on.
OFA has a public database of hip score results from authorized participants.
PENNHIP (University of Pennsylvania Hip Improvement Program)
http://www.vet.upenn.edu/research/centers/pennhip//
The PennHip method of hip evaluation is a tool for the prediction of the onset of osteoarthritis or DJD through the
measuring of joint laxity or the distance a femoral head can be distracted from the socket in an anesthetized dog
resulting in a numeric value known as a DI (distraction index .0 to 1.0). The median DI range is different for every
breed of dog, but what remains constant is the tighter the hip DI the less likely for an animal to develop DJD. PennHip
will xray and assign right/left hip DI's to dogs as young as 16 weeks, but does not recommend initial submission until
12 months.
Procedure: The PennHip method requires 3 xrays for evaluation: the compressed view where the dogs hips are
pushed fully into the sockets to measure hip congruity, a distraction view where the dogs hips are pulled horizontally
from the sockets until the round ligament connecting the two has been extended fully to determine the DI and the hip
extended (OFA) view from above to determine hip conformation and to look for signs of DJD..
PennHip uses scientific measuring tools for all submitted xrays and is not subjective, yet very exact in its
measurements. Veterinarians must be certified to take PennHip xrays and must complete a series of seminars on
proper positioning and technique.
Pennhip has a large scientific database of all DI scores by breed, but it is not available to the public.
FALSE POSITIVE RATES
As with any testing false positive rates will come into play. You do not find a whole lot of information on them because
its like admitting your way is not the perfect way. The false positive rates for PennHip are significantly greater than
with OFA. The reason behind this is that OFA only requires one xray to be submitted (usually the best one) therefore
limiting the number of "bad" xrays that are viewed and PennHip requires ALL xrays be it 4 or 10 be submitted so there
is a greater number of xrays in the pool so to say.
False Positive Rates:
PennHip: 48% age 4 months, 57% age 6 months and 38% age 12 months
12% of dogs said to be normal at 4 months of age were later determined to have DJD. 48% of the dogs said to be
abnormal at 4 months of age, 57% at 6 months of age and 38% at 12 months of age did not show any signs of DJD by
the age of 24 months. Another study showed that while a DI of less than .40 is 88% reliable in predicting normal hips,
a DI of more than .40 is only 57% reliable in predicting abnormal hips.
OFA: 17.6% age 3-6 months, 10% age 7-12 months and 8.5% age 13-18 months.
So as far as preliminary evaluations of young dogs, I feel OFA has a better record with predictability. Although neither
OFA or PennHip should be taken at face value until the dog has reached the age of 24 months. The hip structure is
in a constant state of change between 3 to 12 months and it is necessary to have any dog re-evaluated that was
originally xrayed under 15 months of age.
THE IMPORTANCE OF GOOD POSITIONING OF XRAYS
Positioning faults and technical deficiencies may result in non diagnostic radiographs or the illusion of hip disease
where it does not exist.
Strict adherence to the correct positioning standards is a prerequisite for accurate radiographic assessment of hip
structures. Major problems caused by variations from it include distortions of the acetabular depth and contours, the
illusion of femoral head sub luxation (see image "A" below), and distortion of the femoral neck angle. Each of these
variations can mimic signs of disease and lead to diagnostic errors.
(http://www.cal.vet.upenn.edu/saortho/chapter_83/83mast.htm)
Below you will see Image "A" and Image "B". Image "A" is a badly positioned xray. You will see that the pelvis is
rotated so you see the wing of the ilium (hip bone) and it appears thicker(red arrow) on one side but not the other.
The right acetabulum appears more shallow and there is incongruent sub luxation of the femoral head as well as a
thicker look to the femoral neck(green arrow). The left hip appears to have minor signs of DJD on the weight bearing
surface of the femoral head(yellow arrow). The entire pelvis is tilted as well causing non-uniformity to the
sockets(blue arrows). In Image "B" the wings of the ilium are even and distinct. The acetabulum are of even depth
and size. The femoral heads and necks appear free of DJD. This is a well positioned xray of normal canine hips.
Note: Image "A" and "B" are of the same dog.
Image "A" Image "B"
References:
University of Pennsylvania Veterinary Education Dept.
University of Pennsylvania Hip Improvement Dept.
Orthopedic Foundation for Animals
G.G. Keller, DVM, MS, Diplomate of AVCR - Executive Director of the OFA
E.A. Corley, DVM, PhD, Diplomate of AVCR
Fred Lanting, Breeder/Judge 1998
Wendall Belfield, DVM
Lastly, I would like convey my thoughts on a popular myth. Through speaking to many orthopedic professionals I
have come to the conclusion that it is possible to make good hips look bad through poor positioning, but extremely
difficult for any xray technician or veterinarian to hide true hip dysplasia or degenerative joint disease.
Thanks for reading!
Monique Laperriere
Through this article, I would like to dispel myths and enlighten you regarding the FACTS on hip xrays.
Over the past two years, I have read study after study and done a great deal of research covering the topics of OFA,
PennHip and Hip Positioning. I DO NOT believe either OFA or PennHip to be more superior than the other, but BOTH
useful tools in determining the status of the canine hip.
The information here was compiled referencing the people listed at the bottom of the page.
OFA (Orthopedic Foundation for Animals)
http://www.offa.org
Procedure - The dog is placed on its back. The hind legs are extended fully in a caudal (away from the rear end)
direction, held parallel and rotated fully in a medial direction. When this position has been achieved, the cranial(top)
mid line of the femora(plural for femur-thigh bone) will face up directly toward the xray machine. Sedation may be
required to achieve this position in all but the most cooperative dogs. OFA does recommend sedation, but does not
require it. Always remember this positioning is NOT normal for the canine hip and if the animal is not sedated can be
extremely uncomfortable.
OFA offers preliminary hip dysplasia(HD) screening on dogs as young as 4 months old, but will not CERTIFY a dogs
hip status until 24 months of age. The reasoning behind this is that the animal has not finished growing. Since true
HD (abnormal development or an abnormal structure resulting from such growth) is usually evident within the first year
of a dogs life, an OFA Preliminary evaluation is an excellent tool for assessing breeding stock early. HD is the primary
cause of DJD(Degenerative Joint Disease - a debilitating disease that breaks down the cartilage and remodels the
bones of the hip), but not the only cause of DJD. For example: A canine athlete may show minimal signs of DJD
without ever having HD in the same way a human athlete will. If your dog is a canine athlete: protection sport, field
work, agility or even SAR(search and rescue) you should send a letter in with you're dog's xray stating what arena(s)
the dog is active and for how long the dog has been doing it. The evaluating veterinarians will take that information
into consideration when reviewing the xrays.
There are seven levels of HD as diagnosed by OFA:
EXCELLENT - Superior hip joint conformation(tight joint space and almost complete coverage of the femoral head) as
compared to other dogs of the same breed and age.
GOOD - Well formed hip conformation, most of the socket covers the femoral head but there is congruent(even) joint
space.
FAIR - a) There is congruent joint space, but the socket's weight bearing surface is deviated inward
b) The joint space is slightly incongruent, but still with good femoral head coverage.
BORDERLINE - There is no clear cut evidence for the evaluating veterinarians to put the hips in either normal or
dysplastic category and re-xray and submission is suggested in 6 months.
MILD - There is significant sub luxation present where the ball is partially out of the socket causing incongruent joint
space and the socket is shallow. There are usually no arthritic changes in dogs 24-30 months. Re-submission is
suggested as the dog ages.
MODERATE - There is substantial sub luxation of the ball from the joint where the ball barely fits into the joint
anymore. There are secondary arthritic changes along the femoral head, neck and acetabular rim(socket edge).
SEVERE - There is significant sub luxation present where the ball is either partially or completely out of a shallow
socket and always large amounts of arthritic changes to the whole joint area.
OFA is a subjective test where two to three vets look at the xrays and give there "opinion" of the hip status. For
example: 2 vets say FAIR, 1 vet says GOOD..the dog scores a FAIR. One says EXCELLENT, one says FAIR, one
says GOOD... the dog scores a GOOD and so on.
OFA has a public database of hip score results from authorized participants.
PENNHIP (University of Pennsylvania Hip Improvement Program)
http://www.vet.upenn.edu/research/centers/pennhip//
The PennHip method of hip evaluation is a tool for the prediction of the onset of osteoarthritis or DJD through the
measuring of joint laxity or the distance a femoral head can be distracted from the socket in an anesthetized dog
resulting in a numeric value known as a DI (distraction index .0 to 1.0). The median DI range is different for every
breed of dog, but what remains constant is the tighter the hip DI the less likely for an animal to develop DJD. PennHip
will xray and assign right/left hip DI's to dogs as young as 16 weeks, but does not recommend initial submission until
12 months.
Procedure: The PennHip method requires 3 xrays for evaluation: the compressed view where the dogs hips are
pushed fully into the sockets to measure hip congruity, a distraction view where the dogs hips are pulled horizontally
from the sockets until the round ligament connecting the two has been extended fully to determine the DI and the hip
extended (OFA) view from above to determine hip conformation and to look for signs of DJD..
PennHip uses scientific measuring tools for all submitted xrays and is not subjective, yet very exact in its
measurements. Veterinarians must be certified to take PennHip xrays and must complete a series of seminars on
proper positioning and technique.
Pennhip has a large scientific database of all DI scores by breed, but it is not available to the public.
FALSE POSITIVE RATES
As with any testing false positive rates will come into play. You do not find a whole lot of information on them because
its like admitting your way is not the perfect way. The false positive rates for PennHip are significantly greater than
with OFA. The reason behind this is that OFA only requires one xray to be submitted (usually the best one) therefore
limiting the number of "bad" xrays that are viewed and PennHip requires ALL xrays be it 4 or 10 be submitted so there
is a greater number of xrays in the pool so to say.
False Positive Rates:
PennHip: 48% age 4 months, 57% age 6 months and 38% age 12 months
12% of dogs said to be normal at 4 months of age were later determined to have DJD. 48% of the dogs said to be
abnormal at 4 months of age, 57% at 6 months of age and 38% at 12 months of age did not show any signs of DJD by
the age of 24 months. Another study showed that while a DI of less than .40 is 88% reliable in predicting normal hips,
a DI of more than .40 is only 57% reliable in predicting abnormal hips.
OFA: 17.6% age 3-6 months, 10% age 7-12 months and 8.5% age 13-18 months.
So as far as preliminary evaluations of young dogs, I feel OFA has a better record with predictability. Although neither
OFA or PennHip should be taken at face value until the dog has reached the age of 24 months. The hip structure is
in a constant state of change between 3 to 12 months and it is necessary to have any dog re-evaluated that was
originally xrayed under 15 months of age.
THE IMPORTANCE OF GOOD POSITIONING OF XRAYS
Positioning faults and technical deficiencies may result in non diagnostic radiographs or the illusion of hip disease
where it does not exist.
Strict adherence to the correct positioning standards is a prerequisite for accurate radiographic assessment of hip
structures. Major problems caused by variations from it include distortions of the acetabular depth and contours, the
illusion of femoral head sub luxation (see image "A" below), and distortion of the femoral neck angle. Each of these
variations can mimic signs of disease and lead to diagnostic errors.
(http://www.cal.vet.upenn.edu/saortho/chapter_83/83mast.htm)
Below you will see Image "A" and Image "B". Image "A" is a badly positioned xray. You will see that the pelvis is
rotated so you see the wing of the ilium (hip bone) and it appears thicker(red arrow) on one side but not the other.
The right acetabulum appears more shallow and there is incongruent sub luxation of the femoral head as well as a
thicker look to the femoral neck(green arrow). The left hip appears to have minor signs of DJD on the weight bearing
surface of the femoral head(yellow arrow). The entire pelvis is tilted as well causing non-uniformity to the
sockets(blue arrows). In Image "B" the wings of the ilium are even and distinct. The acetabulum are of even depth
and size. The femoral heads and necks appear free of DJD. This is a well positioned xray of normal canine hips.
Note: Image "A" and "B" are of the same dog.
Image "A" Image "B"
References:
University of Pennsylvania Veterinary Education Dept.
University of Pennsylvania Hip Improvement Dept.
Orthopedic Foundation for Animals
G.G. Keller, DVM, MS, Diplomate of AVCR - Executive Director of the OFA
E.A. Corley, DVM, PhD, Diplomate of AVCR
Fred Lanting, Breeder/Judge 1998
Wendall Belfield, DVM
Lastly, I would like convey my thoughts on a popular myth. Through speaking to many orthopedic professionals I
have come to the conclusion that it is possible to make good hips look bad through poor positioning, but extremely
difficult for any xray technician or veterinarian to hide true hip dysplasia or degenerative joint disease.
Thanks for reading!
Monique Laperriere
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