HIP AND ELBOW DYSPLASIA 

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DR. R S Wyburn BVMS. DVR. PhD, FACVSc. MRCVS.

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OVERVIEW

Canine hip dysplasia (HD) is a genetic disease which is inherited in a rather complex manner because it is influenced by more than one gene.
That is its mode of inheritance is polygenetic. HD was first recorded back in the 1930s but its incidence has increased as the popularity
of breeding and showing dogs has increased. Whether this is coincidence or whether there is some relationship has not been established.
In a number of breeds the disease is present in some degree in over 80% of individuals. Because of this it is important that a control programme is put in place. The control programme should require that all individuals that are to be bred from have their hips scored and a score should be set above which breeding is not recommended.

Obviously the ideal situation would be to breed only with dogs that have a 0 score. However this is unacceptable as doing so could exclude most if not all of the breed. A compromise has to be reached which will allow the retention of sufficient breeding stock but which will decrease the severity and incidence of the disease. It is up to the breed society to set standards that are acceptable for breeding.

A basic guideline is as follows:
If the score for any one hip is greater than 8 or if the score for any one of the 9 features listed on the score sheet is greater than 3 the dog should not be bred from. Once sufficient numbers of the breed have been assessed (100) an average for the breed can be established and then the selection criteria should be that no one hip should have a score of greater than ½ the average score.
As the breed average score drops so will the score that is acceptable for breeding.

Such a control programme can be taken a step further by recording the hip status of offspring so that it can be determined which sires are tending to reduce the hip scores of their progeny.

THE SCORING SYSTEM

HIP SCORE
Hip Right Left

• Norberg Angle _______________________

• Subluxation _______________________

• Cranial acetabular edge _______________________

• Dorsal acetabular edge _______________________

• Cranial eff. acet. rim _______________________

• Acetabular fossa _______________________

• Caudal acetabular edge _______________________

• Fem neck exostosis _______________________

• Fem head recon touring _______________________

• Total _______________________

• Score ______

The 9 items listed on the scoring sheet are all details of the anatomy of the hip joint that can be seen on an x-ray film.
Of these features 8 are scored out of 6 with 0 being normal.
One of these, the Caudal Acetabular Edge, is scored out of 5.
Therefore the worst possible score for each hip is 53 with the worst combined score being 106. 

THE GRADING SYSTEM

There is not a direct relationship between scoring and grading which causes considerable confusion.
The grading is done on the worst hip only. Because of differences in the assessment methods it is possible, though uncommon, for dog with a relatively low score to have a relatively high grade.
Generally speaking it is considered acceptable to breed from dogs with grades 0, 1, 2, and 3 and not
from grades 4, 5, and 6.
It is probable that the grading system will stop being used sometime in the near future.

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HIP DYSPLASIA

The hip joint is a ball and socket joint with the ball (femoral head) being on the proximal end of the thigh bone (femur) and the socket (acetabulum) being on the pelvis. If the hip joint is normal the ball is a neat fit in the socket.
Generally all new born puppies have normal hip joints but in those that have HD an abnormality develops during growth.
The problem appears to be in the growing of the socket. For the socket to grow bigger as the dog grows requires quite a complex process because it is difficult to grow a hole. With the acetabulum this is achieved by the three bones that make up one side of the pelvis (ilium, ischium and pubis) joining at the acetabulum thus forming a complex pattern of growth zones.
If the acetabulum is to develop correctly the growth rate at these different zones has to be precisely matched.
If it is not, the acetabulum will become distorted so that the ball is no longer an accurate fit and this is hip dysplasia.
Some recent research suggests that dogs with HD have problems with other bone growth zones but because these are mainly involving single bones they do not cause problems. 

Hip dysplasia in itself does not commonly cause lameness.
It only does so if it is of such a degree that the hip dislocates and this is uncommon.
So many dogs, particularly younger dogs, with hip dysplasia show no signs of lameness.
This combined with the fact that it is a developmental abnormality is the reason why we have to resort to assessing dogs for hip dysplasia from an X-ray taken when the dog is at least 12 months of age.

With dogs that have HD the ball is not a neat fit in the socket so the joint is subject to excessive wear and tear.
This excessive wear and tear results in the development of degenerative joint disease (arthritis).
It is the arthritis that causes the lameness. Other factors can impact of the degree of wear and tear the joint is subjected to.
The two main ones are the weight of the dog and the amount and type of exercise the dog takes.
Obviously the heavier the dog the more stress is put on the hip joint so large heavy dogs are more likely to become lame because
of hip dysplasia than small light ones. Dogs that get a lot of exercise at fast gaits such as galloping behind a car or bicycle and
dogs that do a lot of jumping or turning and stopping such as when fetching balls or sticks stress the hip joints and are therefore
more likely to become lame. A normal hip joint can sustain these sorts of stresses without developing arthritis.
So the age at which a dog with HD shows signs of lameness and the severity of the lameness is influenced by an inherited component.
That is the degree of developmental abnormality of the joint.
Then there is the environmental influence which is the degree of stress the joint is subjected to.

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ELBOW DYSPLASIA

Elbow dysplasia is a disease with a high inherited component, which primarily affects intermediate and large breed dogs.
A high incidence of occurrence has been noted in some terrier breeds.
Typically, both elbows are affected. However, unilateral elbow dysplasia is not uncommon.

 

DEVELOPMENT 

The elbow joint is composed of three bones (radius, ulna, and humerus) which must all grow together and fit perfectly.
The radius and ulna are paired bones with the radius being the main weight bearing bone.
The normal elbow joint is characterized by a smooth transition from the ulnar articular surface to the radial surface.
In a dysplastic elbow the edge of the ulnar surface lies above the level of the adjoining radius, creating a step between
the radius and ulna and causing incongruity of the joint.

The height of the step may vary from barely noticeable to 4 mm or more.
When this occurs the weight bearing force on the ulna is increased, resulting in excessive pressure on the medial coronoid process.
This leads to fragmentation of the coronoid process. This usually occurs between 5 and 7 months of age.
A superficial to deeply grooved "kissing lesion" is often present on the humeral articular surface opposite the fragment.
A cartilage flap or OCD (osteochondritis dissecans) lesion may also develop.
Secondary arthritis becomes evident at 6-7 months.
Compensatory adjustments during growth may occur in some dogs, tending to minimize unequal growth rates between
the three bones and moving the ulna distally to better conform to the radius.
However, excessive force is then placed on the anconeal process at the top of the ulnar articular surface.
This force will cause a failure of ossification, leading to an ununited anconeal process. (UAP)

 

CLINICAL SIGNS

Affected dogs are frequently lame or have an abnormal gait.
The gait is often characterized by excessive paddling or flipping of the front feet.

The animal may either hold the elbows out or tucked in and often stands with the feet rotated outward.
Many sit or lie down much of the time, or play for shorter periods of time than other dogs of comparable age.
They are often described as quiet or even lazy. Frequently, they are stiff when rising and tire easily.
Exercise typically makes the lameness worse.
In dogs with bilateral elbow dysplasia, the lameness may seem intermittent or shift from one front leg to the other.
When both front legs hurt, dogs do not limp constantly.
Rather, they shift weight off their elbows by altering their gait and stance.
These dogs will only "limp" when one elbow is more painful than the other.
On examination, manipulation of the elbow is often resisted.
Swelling and crepitus (grating) may be palpated.
The swelling may be worse after exercise.
In some cases, the joint will be thickened. Muscle atrophy may also be present.

 

DIAGNOSIS

The routine monitoring for the presence of elbow dysplasia is carried out from a lateral x-ray of the flexed elbow joint
taken when the dog is over 12 months of age. Correct radiograph technique is critical for making the diagnosis.
The grade is derived by measuring the amount of new bone that has developed as a result of arthritis.
Unlike the grading systems for hip dysplasia the system for elbow dysplasia is used internationally. 

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ADVICE

It is generally considered that dogs with grade 3 elbow dysplasia should not be used for breeding and that dogs with grade 2 should be considered a serious risk.