EE was removing equipment. He climbed the ladder of the jib crane to top of the loader. The finder on right side is used as a landing support for ascending & descending the ladder. He fell & slipped off falling onto the tire then to the floor. Swelling in ankle. Diagnosis: Acute exacerbation osteoarthritis right knee: occupational illness. Rst on 6-11-13, Lost time on 9/4/13.