WHILE CLEANING ROCKS & DEBRIS FROM TOP OF GRIZZLY, EMPLOYEE'S FOOT SLIPPED BETWEEN BENT PIPING. (GRIZZLY IS BUILT WITH 2"" PIPING SPACED APPROX. 3"" APART). HEAVY ROCKS HAD BENT PIPING ALLOWING ENOUGH SPACE FOR HIS FOOT TO SLIP THROUGH (HE WAS WEARING HARNESS & LANYARD). RIGHT KNEE CAUGHT BETWEEN PIPING, TWISTING KNEE & CAUSING HIP PAINS.