Reported late on 3/31/03: while loading a hoist pedestal pin into a maint. truck the EE slipped in a muddy area he stepped into and strained his left knee. The EE initially reported to his shop supervisor on 3/27/03 and (allegedly) reported to the 8750 outage supervisor on 3/31/03. The EE was given first aid treatment and returned back to full duty the same day.