WORKER WAS IN A SQUATTING POSITION FOR AN EXTENDED PERIOD OF TIME WELDING ON A TRAILER LID. WHILE SQUATTING, LEFT LEG ROLLED OUTWARD CAUSING A STRAIN TO KNEE. HE HEARD A ""POP"" AND PAIN ENSUED. WORKER REPORTED THE INCIDENT AS A MINOR INJURY. NO FIRST AID OR MEDICAL TREATMENT WAS RENDERED. OVER ENSUING MONTHS, THE KNEE ""POPPED"" SEVERAL TIMES. ON 12/10/03 HE SOUGHT MEDICAL TREATMENT