MECHANIC WAS USING A 6 FOOT STEPLADDER TO CLIMB OFF OF A ROCK TRUCK HE HAD BEEN WORKING ON. LADDER SLIPPED & TIPPED OVER. EE FELL ONTO LADDER STRIKING HIS BACK. EE WAS DIAGNOSED AS HAVING A CO NTUSION WHICH WAS CAUSING MUSCLE SPASMS. EE WAS PLACED ON RESTRICTED DUTY UNTIL JUNE 17TH.