Elbow dysplasia is a relatively common condition affecting the normal development of elbows in dogs. Various abnormalities can be found and in this particular case the elbow joint surface is not smooth and has a "step" in it as a result of the growth plate in the radius closing early. This means that the radius bone stopped growing in length where the ulna bone next to it continued to grow, making the joint surface uneven and causing pain for the dog as a result.
