DURING THE PROCESS OF MAKING PREHEATER ADJUSTMENTS, THE EMPLOYEE WAS WALKING DOWN AND UP STAIRS. DENIES ANY TRAUMA, STATING THAT FELT A PAIN IN LEFT KNEE WHILE RETURNING UP STAIRS. UPON INSPEC TION OF KNEE, DISCOVERED SWELLING 2 CM X 3CM ON LOWER MEDIAL ASPECT OF KNEE. NO DISCOMFORT STANDING OR WALKING, ONLY WHEN BENDING DX AS STRAIN.