EMPLOYEE WAS BOLTING IN A SLAB CUT FOR THE CROSSCUT BETWEEN ENTRY #4 & #5 IN UNIT #1. HE WAS BOLTING WITH ANOTHER EMPLOYEE. HE STATED THAT AS HE PULLED UP ON THE SLAB JACK, IT CAUGHT ON A ROCK AND HIS FOOT SLIPPED OFF OF THE ROCK, TWISTING HIS RIGHT KNEE. BECAME REPORTABLE WHEN HE HAD FLUID DRAINED FROM HIS KNEE