In 2004, I got my PhD on the subject 'Breeding against hip and elbow dysplasia in dogs'. My conclusion was that it is possible to breed against these traits and that not much has happened though. The reason was that no systematic selection has in practice been made against these defects.
Now, 11 years later, I am glad to see that Finnish breeders have managed to achieve genetic as well as phenotypic gain. St Bernards have also increased their lifespan, as their health has been improving.
The Finnish Kennel Club started to estimate breeding values (EBVs) for hip and elbow dysplasia in 2002 for 11 breeds, and during the years, new breeds have been included. At the moment somewhat 55-60 breeds have EBVs for hip dysplasia.
It is possible to achieve genetic gain if the breeding dogs are systematically chosen from the better half of the population. There is no need to breed only from animals from the very best hips; just those that are better than the breed average. Progress will be slower, but doing it this way helps maintain genetic diversity.