Any breed can be affected. It is not the length of leg that predisposes a puppy or a litter to this problem. The condition is not necessarily hereditary, even though it may occur repeatedly in the litters of one bitch.
All puppy bones are little more than rubber bands in their first weeks of life.
If you notice the shape of the chest of your puppies as they are born, you will see a normal oval shape, with the long axis vertical. As puppies crawl around the whelping box and nurse, often they begin to acquire a more flattened shape, with the long axis of the chest becoming more and more horizontal. Factors which contribute to this are 1. Excessive milk consumption - due to a mother with great deal of milk willing to stay in the whelping box for long stretches. This is what accounts for repeated litters of swimmers from one bitch.