In unaffected dogs there is a good fit between ball and socket. An easy way to think about it is to imagine a tennis ball and a cup. If you put the ball into the cup there is a good fit. If you put the ball into a saucer, it will roll around loosely. This poor fit between femoral head and acetabulum is characteristic of dysplastic dogs.

Affected dogs are not born with HD, only with the makings of it. As puppies grow, laxity of the muscles and ligaments surrounding the joint and the poor fit between the bones produces excess movement of the ball in the acetabulum. The separation between the bones is called subluxation, and at its most severe it can become a total dislocation (the head of the femur leaves the acetabulum). The surfaces of the bones start out completely smooth, but with HD changes take place. Bone rubbing against bone causes irritation which results in irregular bone growth and wear on the articular surfaces. These irregular surfaces result in Osteoarthritis, which can cause significant pain. As the bone of the acetabular rim is ground away, the socket becomes shallower and it is more difficult to keep the head of the femur properly seated.

Outward signs of hip dysplasia can range from none to severe pain. The dog's movement may or may not be affected. Some outward signs that MAY be seen in affected dogs are:

• Difficulty getting up from a lying or sitting position or in climbing stairs.
• A bunny hop gait (moving both rear legs together).
• A painful reaction to extension of the rear legs.
• Pushing on the rump may cause the pelvis to drop.
• When rolled over, some affected dogs will resist having their legs spread into a frog-leg position.
• A side to side sway of the rump.
• Dogs may avoid jumping
• Lameness may be seen, especially after strenuous exercise.

It is very important to understand that the only way to accurately diagnose HD is through x-rays, since the above symptoms may also be seen in dogs with normal hips; furthermore, affected dogs may display none of these symptoms at all.

The X-ray photographs below illustrate various degrees of severity of the dysplastic condition. The normal hips on the left are free of dysplasia, as shown by the tight and full fit of the ball in the socket, and by the U-shaped notch in the neck; the hips on the right exhibit mild dysplasia in the right hip, as evidenced by the slight flattening of the head of the femur and by the socket not being as round as it could be.

   
Normal Hips                                    Mild Dysplasia on Right Side

The x-ray photographs below both show a severe degree of dysplasia, accompanied by degenerative joint disease, and the effects of the wearing away of both the ball and the socket (acetabulum) can be clearly seen. In both of these cases the dog in question would have experienced difficulty in movement and probably a very great deal of pain and discomfort. In the picture on the left, the arrows point to the thickened femoral neck on each side, as well as the secondary arthritis occurring on the left hip. Note the flat sockets and the non-rounded appearance of the femoral head. The extreme case on the right is nearly as bad as it gets, causing crippling lameness and severe pain.

   
Severe Dysplasia                                    Extreme Dysplasia

CAUSES

• HD is a complex inherited disease whereby the degree of severity of dysplasia in the parents directly influences the frequency and severity in the pups. Even mild dysplasia in one parent will affect the risk of dysplasia developing in their offspring.
• A high energy diet leading to rapid growing or overweight pups has a greater chance of producing dysplasia, especially if the growth spurt occurs at a sensitive time in skeletal and muscular development.
• Excessive activity in the young animal, especially if overweight or in the presence of exaggerated joint laxity, can aggravate dysplasia.
• Calcium intake may be an important factor with both excessive or insufficient calcium being detrimental to joint development.

GRADING OF HIP DYSPLASIA IN SOUTH AFRICA

Grade 0 :	No signs of hip dysplasia.
Grade I :	Mild shallowing of acetabulum and flattening of femoral head.
Grade II :	Moderate changes.
Grade III :	Severe changes.
Grade IV :	Very severe changes

Breeding from HD free dogs will not necessarily guarantee that their offspring will be HD free. An HD control programme in Sweden showed that:

Normal to Normal matings produced 18% dysplastic offspring.

Normal to Dysplastic matings produced 59% dysplastic offspring.

Dysplastic to Dysplastic matings produced 87% dysplastic offspring.

CONCLUSION

Since HD is caused by the genetic make-up of the parents, the only way to minimise the incidence of HD in puppies is to use breeding stock that is as HD-free as possible. Even this will not eliminate the incidence of HD, but can only reduce it. The owner of the puppy can, in turn, minimise the incidence of aggravating factors that would make things worse, especially during the pup's first year of growth.

REFERENCES

Hip Dysplasia: Understanding the Condition and its Treatment; Dr Race Foster and Dr Marty Smith.

Canine hip Dysplasia: Cheryl Minnier.

Canine Hip Dysplasia in South Africa: Dr Mark Rubinsohn.

X-rays: Long Beach Animal Hospital, Long Beach USA; www.lbah.com