EE was rock dusting belt line. Was walking backwards and tripped on a hump in the mine floor. Lost his footing and twisted his left knee. REPORT IS BEING SUBMITTED ON 03/18/2016 DUE TO FACT HE HAS BEEN AT WORK UNRESTRICTED ON HIS NORMAL JOB UNTIL 3/14/2016. HE WAS EXAMINED BY A DOCTOR ON 3/15/2016 MEDICAL CARE WAS ADVISED FOR EE REQUIRING LOST WORK DAYS.