EE WAS CLEANING THE XXXX MATERIAL BUILDUP ON THECHALK STACKER. THE EE WAS ASCENDING A CAGED LADDER FROM THE TURNTABLE TO THE BOOM. THE TOP SUPPORT ON THE LADDER BROKE CAUSING THE LADDER TO LEAN OUT. THE EE HIT HIS BACK ON THE INSIDE OF THE CAGE WHILE HOLDING ON TO THE LADDER. STARTED PHYSICAL THERAPY ON 11/20/01, PUT ON LIGHT DUTY 12/18/01.