EE left his tools on barge he was loading earlier. Went down the gangway to pick up tools and a tug with 6 barges ran into dock and barge he was on shifted he fell to barge. Right knee started to swell that morning. 2 weeks later he was starting to load another barge & picked up on gangway to put on barge when his knee failed & he fell to the ground. Happened on 8/10/11.