Went in early on this day. Walking across the section to see what areas needed cleaning. Walked in the crosscut between #2 & #3 entries, he stepped across a rut in the floor made by a scoop tire and hyper-extended right knee. Continued working and did not seek medical attention until 3/26/10 on scheduled day off. Saw dr. due to pain, 1st day missed was 3/29/10.