EMPLOYEE WAS LYING IN A PRONE POSITION WORKING ON REPLACING TWO SIZING SCREENS WHEN HIS LEFT FOOT BECAME CAUGHT BETWEEN TWO SCREEN SUPPORTS. IN THE PROCESS OF TRYIN GTO FREE HIS BOOT, HE TWI STIGED HIS LEFT KNEE OUT OF JOINT. EMPLOYEE HAD SURGERY TO REPAIR LEFT KNEE IN 1990 AND STATED THA KNEE HAS DISLOCATED SEVERAL TIMES SINCE AT HOME.