EMPLOYEE WAS WALKING UP A RAMP OUTSIDE THE MAINTENANCE SHOP CARRYING MATERIAL TO A JOB SITE AND FELT LEFT KNEE POP AND GET VERY WARM. KNEE CONTINUED TO POP IN AND OUT THE REST OF THE DAY. EMPLOYEE DECIDED TO SEE A DOCTOR ON 6-12-12. EMPLOYEE CONTINUED TO WORK FULL TIME THRU 6-27-12. HE WENT IN FOR KNEE SURGERY ON 6-28-12.