Employee was in the process of cleaning entry 0 with scoop. As he was scooping inby he tore down part of the curtain. Employee backed scoop outby the curtain he tore down. Employee climbed out of the scoop to go rehang the curtain. As he walked over to the curtain to pick it up employee stepped on a lump of coal and twisted his right knee. Employee had surgery on 4/6/12.