EMPLOYEE WAS CLIMBING UP THE STAIRS, WHEN LEFT FOOT WAS CAUGHT UNDER THE STAIR STEP. EMPLOYEE SLIPPED DOWN TO THE NEXT STAIR STEP AND LANDED ON LEFT ANKLE. EMPLOYEE BROKE LEFT ANKLE ON IMPACT AND MANAGED TO WALK DOWN THE STAIR ONTO LEVEL GROUND FLOOR AND CONTINUE TO WALK 20' TO A PARKED PICKUP TRUCK, WHEN EMPLOYEE COLLAPSED ONTO BACK.