Canine hip dysplasia is a congenital, inherited malformation of the hip joint where the ball or head of the femur does not fit snugly into the socket. If the cartilage that lines and cushions the hip joint is damaged by trauma or excessive exercise (especially as a puppy) it loses its thickness and elasticity. This in turn reduces its shock-absorbing qualities as the joint attempts to stabilise itself during movement and a cycle of damage, inflammation and pain occurs. In addition to excessive exercise, hip dysplasia is also influenced by other environmental factors such as obesity. There are a number of dogs with dysplasia who may have severe arthritis but be able to run, jump and play as if nothing were wrong and others with minimal radiographic changes that show severe lameness.
It is not possible to tell the hip status of a dog without X-rays and we encourage all breeders to have their dogs screened before breeding to ensure that genetic factors are kept to a minimum. Fortunately the Smooth Collie does appear to have low scores but very few are tested and it would be very easy to be complacent and unaware that a problem has crept into the breed.