Hip Dysplasia

There are many excellent sites providing information on Canine Hip Dysplasia.  The purpose of this page is to collate together data specific to the Basenji breed and provide a basic understanding of Canine Hip Dysplasia and the testing available for this disease.

Firstly, what is Canine Hip Dysplasia?

Hip Dysplasia is abnormal development of the hip joints which results in degenerative changes such as arthritis.  Hip Dysplasia is characterised by shallow sockets, abnormal heads and necks of the femur and from excessively loose ligaments.

Is Canine Hip Dysplasia hereditary?

Hip Dysplasia is a polygenetic inherited condition that is affected by environmental influences such as weight, diet and exercise.  There are several different genes responsible and some are masked so an animal may carry the genes for Hip Dysplasia without displaying any signs themselves. This means that parents with normal hips can produce offspring with Hip Dysplasia.   The disease is even more complex because dogs with no clinical signs can have severe changes in hips when radiographed.  It can therefore not be assumed that if your dog moves and gaits normally that it is free from Hip Dysplasia.  Lameness is rarely apparent in a dog unless it has severe Hip Dysplasia.

Hip Dysplasia test results data in the Basenji

The tables below show data available, by country

Trends in USA

As can be seen the number of Basenjis which have been tested for Hip Dysplasia is low comparative to the overall population.  For effective utilisation of hip reporting schemes a high level of participation by breeders (>90%) is necessary.  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.  

In Australia what is the procedure for having hips scored?

Find a good vet which has experience in taking hip x-rays as it is important that the dog is positioned correctly on the x-ray table to get a good view of the hips.  In order for the vet to position the dog correctly your Basenji will need to be put under a general anaesthetic.  When you make the hip x-ray appointment check with the vet how long before your Basenji must be fed nil by mouth and provided with water only.  Also check that they have the Hip Assessment Form.  This is the form that you will send to the Australian Veterinary Association Hip Assessor.  Take with you to the vet the dogs Registration Papers as you will need to provide identification of your Basenji and complete pedigree information on the Hip Assessment Form.  Once your Basenji has had the x-ray you will be given the radiograph in a large envelope.  Your vet should display the x-ray for you and give a general opinion on how the hips look.  It is very important for the breed that you then mail the radiograph and the Hip Assessment Form with the prescribed fee to the AVA Hip Assessor.  The results whether good, bad or average go into the AVA database which helps give a balanced view of the incidence of Hip Dysplasia in the Basenji breed and a more accurate average score for the breed.  The address and fee are indicated on the Hip Assessment Form.  This form will be returned to you with your Basenji's hip score assessment indicating a score for both the right and left hip to reach an overall Hip Score.

How does the Assessor evaluate the hip x-ray?

There are nine criteria.  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.
Please scroll down to the next heading to skip the following detailed category scoring.  You can always come back to it later.

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 a 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. 

What do the hip score results mean for breeding my Basenji?

Hips are a genetic piece of a Basenji but not the only one and so must be kept in prospective to the breed as a whole.

The lowest score for any hip is 0 so a score of 0:0=0 indicates no abnormality in the hip joints.  The highest score a hip can receive is 53 so a score of 53:53=106 indicates severe hip dysplasia.

A normal Basenji hip joint

In the Australian Basenji the current breed average is 7.29.  Dr R S Wyburn AVA Hip Assessor does not recommend breeding from a Basenji which has a single hip score over 4 or total hip score over the breed average.

When selecting breeding partners selecting those Basenjis which have not scored on the same areas will be beneficial to the speed of decreasing hip scores in future generations.  So rather than just selecting Basenjis who have low overall hip scores but which may have scored those points on the same area look to improve on the specific points. 

The first two areas scored, the Norberg angle and subluxation, are considered to be more influenced by environmental factors e.g. excessive weight, which can give a greater degree of looseness of ligament. The other areas scored all involve arthritic changes and are considered to have a high degree of inheritance.

As an example, it may therefore be beneficial to breed a Basenji who has a hip score of 2:2=4 (where the points are from Norberg Angle (NA)) to a Basenji whose hip score is allocated from a different part of the criteria such as 1:0=1 where the one point is from the Cranial acetabular edge (CrAE).

What is the comparison between the Australian Hip Score and overseas Hip Grade?

The first table compares the Australian hip score to the FCI International Grade.  There are detailed definitions of the radiographic criteria used to allocate to these grades. Further, each of these grades has been subdivided into two which helps with the comparison between national grades. So there is A1 and A 2, B1 and B2 and so on.

It is most important that it is understood that the International grading system is on the grading of the worst hip only and not a combination of both hips as is done in Australia and the UK so when the Australian score is related to this system the score is the worst score for one hip not a combined score for both.

Australian comparison to FCI (International Grade)

 
It cannot be emphasised too much that the comparisons given are only approximations to give a guide. There could be glaring anomalies, for example, a dog with a score of 6 in one hip made up of 2 for Noreberg angle and 4 for Subluxation would have to be at least a D1 international grade.

The grading system used in the USA is even more difficult to correlate directly to the Australian scoring system so what follows can only be taken as a fairly rough guide. Here again what is quoted is the score of the worst hip only.

I would like to thank Dr R S Wyburn, BVMS. DVR. PhD, FACVSc. MRCVS for supplying the above comparison charts and Dr M B Willis for supplying Australian & UK data.

References: AVA, BVA, OFA, Swedish Basenji Club

Copyright © Davina Hopkins 2005