World Congress Summary

The following article was taken from the Summer 2003 Newsletter produced by The Tibetan Terrier Breeder And Owners Club.

HIP DYSPLASIA AND PERTHES DISEASE:
WHAT IS THE DIFFERENCE?
By Dr Mike Tempest

Hip Dysplasia, usually abbreviated to HD, is a problem of the hip joint. This joint is a "ball and socket" type of joint, with the head of the thigh bone (the femur) being "the ball" and the pelvic girdle being "the socket" (the acetabulum). In a perfect animal the ball fits tightly into the socket with no looseness. Variations away from a perfect fit occur to cause a badly formed joint, with varying degrees of severity. Indeed, any variation from perfect, no matter how small, can be regarded as dysplasia. As the hip is a joint, there are obviously several components associated with either the "ball" or the "socket" or both that contribute to the problem and these components are all scored in the BVA.KC HD Scheme. However, the most common cause of the problem is one of a shallow 'socket', CAUSING THE "BALL" TO BE LOOSE. To put this into easily understood language, Willis (1989) likened the perfect hip to a cup with a tennis ball placed in it, where there is a very tight fit between the tennis ball and the lip of the cup. At the other extreme, he likened a very severely dysplastic hip to a saucer with a tennis ball rolling around loosely upon it. There will, of course, be a wide range in the degree of dysplasia as the shape of the socket varies from "cup" to "saucer".

Perthes Disease is just my simple abbreviation of the longer and more correct name of Calve-Perthes Disease, which is also known as Legg-Perthes Disease (probably named after two scientists who both claim to have discovered the condition). It is a problem of the head of the thigh bone. Whereas the essential problem of HD arises from a shallow socket, in Perthes Disease the problem arises from a degenerative "ball". Here there is some death and decay in the head of the femur, which may become flattened rather than the normal round.

There is enlargement of the neck of the femur, loss of minerals from the bone and some collapse of the bony support of the "ball". As with HD, there is variation in its severity. This then leads to degeneration in the joint, which is where confusion between Perthes Disease and HD often occurs.

One further difference between HD and Perthes Disease is that generally in HD, both hips are similarly affected (the term used is bilateral), whereas in Perthes Disease, one "ball" is a lot worse than the other (unilateral). From the score of the x-ray submitted under the BVA/KC Hip Dysplasia Scheme, this would give a score on one side of the hip much worse than on the other side, particularly in the femoral head/neck exostosis (extra bone deposits) and femoral head recontouring criteria (the other criteria are more associated with the socket and the fit between the ball and the socket).

The main differences are summarised in the table below: