EMPLOYEE WAS OPERATING A DOZER ON THE CLEAN COAL PILE TO ELIMINATE A KNOWN VOID. THE COAL GAVE WAY UNDER ONE CAT, CAUSING THE DOZER TO SLIDE SIDEWAYS INTO A HOLE. HE STRUCK HIS RT. KNEE AND RT. ELBOW AGAINST THE DOOR GLASS, CAUSING A CONTUSION TO HIS RT. KNEE & ELBOW. HE WAS LATER DIAGNOSED WITH A RT. TORN MENISCUS.