EE WAS MOVING 3"" PUMP AT THE HIGHWALL MINER/YOAST PIT, WHEN A LOOSE PIECE OF COAL SLID FROM UNDERFOOT, CAUSING EMPLOYEE TO TWIST HIS RIGHT KNEE. A REPORT WAS MADE, BUT MEDICAL ATTENTION WASN'T NEEDED UNTIL 4/26, WHEN EE RE-TWISTED THE SAME KNEE. EE HAD MRI ON 4/27, BUT THE DR COULDN'T READ IT UNTIL 4/28. EE SCHEDULED SURGERY ON 4/29. DIDN'T BECOME REPORTABLE UNTIL 4/20/04.