- an explanation
for owners and breeders -
This article has been prepared
by Leanne Fitzsimmons by request of Katrina Jeffery of www.maremmano.com
Leanne was, at the time of writing, the practice manager of Veterinary Imaging Associates, a practice
of specialist veterinary radiologists who are members of the Australian
Veterinary Association (AVA) panel of veterinary radiologists certified
to provide hip scoring for canine hip dysplasia. They also provide hip
and elbow dysplasia advice to interested individuals and are also PennHIP®
licensed.
Veterinary Imaging Associates is the only practice in Australia that has two specialist veterinary radiologists
who view each hip evaluation radiograph sent for scoring.
For further information please
call on 1300 300 892 or email on via@online-vets.com
Canine Hip Dysplasia (CHD) is the most common heritable orthopaedic problem seen in dogs. It affects
virtually all breeds of dogs, but is especially problematic in large and
giant breeds. CHD develops into a degenerative condition (osteoarthritis)
of the hip joints.
Conventionally, CHD is diagnosed
radiographically by the presence of degenerative changes and/or subluxation
of the hip. The role of subluxation is crucial in the development of CHD
but is often camouflaged on the most commonly used radiographic projection
of the hips.
Radiographic evidence of osteoarthritis
confirms secondary changes of CHD, characterised by periarticular osteophyte
formation (bone spurs), signs of subchondral bony sclerosis and bony remodelling.
The current system used for scoring radiographs for hip dysplasia in Australia
is based the system devised and used by the BVA/KC. There are nine criteria
(see diagram).
Scores between 0 and 6 are
allocated for all criteria, except the caudal acetabular edge, for which
the maximum score is 5.
Higher scores indicate greater
degrees of radiographic abnormality.
The scores for the right and
left joints are added to give a total hip score.
The anatomical landmarks used
for scoring are illustrated.
For a number of reasons it
is not possible to rigidly standardise the information provided by the
radiographic image of a complex structure such as the hip joint. Some
of these reasons are: - conformation; there is a wide range of variation
both between and within breeds, - position; minor positional variations
are accepted and their effects recognised and taken into account during
the scoring procedure, - radiographic technique; lack of contrast due
to inadequate developing, under or overexposure, failure to use a grid,
grainy film/screen combinations, use of x-ray tubes with large focal spots,
- observer error; (to minimise this in evaluation of abnormalities our
practice, Veterinary Imaging Associates uses two readers to examine each
radiograph).
The
categories being scored are:
Norberg
Angle (NA): gives a measured assessment of several features;
the degree of congruence between the femoral head (FH) and acetabulum;
the length of the cranial acetabular edge (CrAE), which gives a relative
indication of acetabular depth and a measure of coxofemoral subluxation
(laxity).
Subluxation
(SL): is based principally on the degree of congruence between
the femoral head and acetabulum. The general 'fit' of these two components
is assessed by the relationship between the femoral head centre (FHC)
and the underlying image of the dorsal acetabular edge (DAE). The cranial
joint space is seen as a radiolucent shadow between the CrAE and adjacent
cranial articular margin of the FH.
- score of 0 - the FHC
must be medial to the DAE and the cranial joint space uniformly narrow,
with the curve of the CrAE exactly following that of the FH.
- score of 1 - mild
divergence of the cranial joint space, either medially or laterally, with
the FHC remaining medial to the DAE.
- score of 2 - superimposition
of the FHC on the DAE (with the FH in this position, the cranial joint
space will inevitably diverge).
- score of 3 - includes
a wide range of femoral positions, with anything between less than one-half
and more than one-quarter of the FH lying medial to the DAE.
- scores of 4 and 5 - are given for severe degrees of subluxation. - score of 6 - complete
separation of the images of the two components.
Cranial
acetabular edge (CrAE): minor alterations in the shape, contour
and possibly the length of the CrAE are generally believed to be indicators
of poor articular congruence, while more severe changes are clearly consequences
of chronic instability, abnormal marginal wear and remodelling of the
joint.
- score of 0 - the CrAE
should be concave, uniformly curved and match exactly the contour of the
adjacent femoral head with no lateral or medial divergence of the cranial
joint space.
- score of 1 - minor
flattening of the outer quarter of the CrAE with slight divergence of
lateral joint space.
- score of 2 - the CrAE
is flattened throughout most or all of its length and there is usually
both medial and lateral joint space divergence.
- score of 3 - higher
scores are given when there is positive evidence of abnormal wear and/or
remodelling of the edge. Early change is manifested by slight bilabiation,
which shows as cranial curvature of a small outer segment of the CrAE.
- scores of 4 and 5 - are given to progressively more extensive bilabiation and cranial orientation
of the edge. - score of 6 - development of a steep cranial slope.
Dorsal
acetabular edge (DAE): the DAE forms a well defined interface
which traverses the FH almost vertically and extends a little beyond it
cranially and caudally. The clarity with which it can be seen is highly
variable, depending on radiographic technique.
- score of 1 - a minor
change in the contour of the DAE, which is normally slightly curved but
small localised irregularities, seen only on radiographs of exceptionally
high quality, are considered to be within normal limits.
- score of 2 - related
to definitive pathological changes associated with degenerative joint
disease (osteoarthritis), the smallest being minor exostosis, which is
usually seen cranially.
- score between 3 and 6 - progressively increasing new bone formation accompanied by marginal
wear of the edge, which leads to reduction in width of the articular surface
and thus contributes to subluxation according to severity.
Cranial
effective acetabular margin (CrEAM):
- score of 1 - the earliest
detectable abnormalities of the CrEAM are either minor exostosis, usually
in the form of a small, well modelled osteophyte, or slight 'rounding
off' of the junction between the CrAE and DAE, which may be seen in the
presence of a non-bilabiated CrAE.
- score of 2 - more
advanced changes at the CrEAM are indicators of abnormal wear and must
therefore be associated with articular instability. Initially, a small
facet forms on the rim (margin), usually in conjunction with minor bilabiation
of the CrAE. Exostosis may or may not be present.
- scores of 3 to 6 (depending
on severity) - increasing secondary changes lead to the development of
larger facets and exostoses, which can become massive and extend well
up the shaft of the ilium.
Acetabular
fossa (AF): it is well recognised that the acetabular fossa
and notch are sites of bone proliferation in unstable hips, an impression
of the amount of new bone present may be gained from the size and intensity
of indistinctly marginated areas of increased opacity in the region of
the caudomedial acetabulum and obliteration or partial obscuring of the
normally clear radiolucent shadow which represents fat in the acetabular
notch. Detectable bone deposition in the AF is almost always associated
with marked subluxation and the amount tends to increase in proportion
with the increase in the other radiographic hallmarks of secondary osteoarthritis.
Objective numerical scoring of this criterion is difficult, but as changes
are likely to be recorded only in dogs with a total score considerably
higher than average, the importance of a high level of accuracy is diminished.
Caudal
acetabular edge (CdAE): is the segment of the acetabulum which
is subject to the widest range of normal radiographic variation. It is
dependent to a large extent on the pelvis/film angle, but may also be
influenced by individual differences in conformation. Radiographic abnormalities
of the CdAEs are scored between 0 and 5 and changes are due mainly to
exostosis, with signs of wear being apparent only in advanced cases.
- score of 1 - a small
osteophyte on the CdAE.
- score of 2 - new bone
localised laterally and medially adjacent to the acetabular notch.
- scores of 3 to 5 -
are used to record progressively increasing bone proliferation which ultimately
fills the notch and produces extensive remodelling.
Femoral
head and neck exostosis (FH):
- score of 0 - the normal
FH should have a smooth roundish profile but the shape may vary considerably.
- score of 1 - a well
defined, vertically orientated ridge of new bone extending from the base
of the neck towards the trochanteric fossa (Morgan and Stephens 1985).
Correct exposure and good radiographic detail are required to show this
earliest recordable change.
- score of 2 - minor
exostosis, visible on the 'skyline' at the lateral and/or medial margins
- score of 3 - is given
when a distinct collar of new bone is visible around the articular margin.
- scores of 4 to 6 -
denote increasing amounts of periarticular proliferation which at its
most severe, extends to cover the femoral neck and fill the trochanteric
fossa.
Femoral
head recontouring: this criterion is used to record the extent
to which the FH shape is altered as a consequence of instability. Thus,
scores are likely to be awarded only in cases in which secondary changes
are well established, when remodelling occurs as a result of the combined
effects of periarticular new bone formation and loss of subchondral bone
(eburnation) following total destruction of articular cartilage. Recontouring
is difficult to evaluate numerically however
- score of 1 - slight
distortion of the outline of the FH
- score of 2 to 5 -
degrees of flattening and expansion of the articular contour
- score of 6 - permanent
luxation in which the FH is grossly deformed, small and almost conical
in shape.
This system of scoring radiographs
for hip dysplasia has the advantage that the requirement to assess a number
of specific anatomical landmarks ensures relatively objective evaluation
of each joint. In addition, the wide range of score points available permits
small differences between hips to be recorded. It can be assumed with
some confidence that any individual hip score of above 10 will be an indication
either of gross instability or of clearly established secondary change.
For effective utilisation of this hip reporting scheme one must ensure
a high level of participation by breeders (>90%) and rigid compliance
(no shopping for more favourable scores) with recommendation made by the
interpreting radiologists and veterinarian obtaining the radiographic
image. An open register of hip scores is essential to ensure a level playing
field and a record of scores of progeny will add significantly to the
value of recorded information of any dam or sire. Currently, we recommend
using dogs whose score is lower than the breed average. Some breeds have
high 'average' scores (>10) - for these we recommend using dogs with scores
less than 10.
Despite concerted efforts of
organisations like the OFA in the United States, the British Veterinary
Association/British Kennel Club (BVA/KC) and other European groups over
the last 20 to 30 years to screen for CHD employing the extended hip view,
CHD remains common in many breeds.
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