EE overturned a piece of equip. (backhoe) & damaged his knee by an unknown cause. Possible torn acl in left knee. EE was seat belted in. (REPORTABLE AS OF 7/20/05: PHYSICIAN ORDERED KNEE BRACE FOR EE TO WEAR; EE ON RESTR. DUTIES. EE WILL PROBABLY HAVE REPAIR SURGERY IN JULY. INCIDENT HAPPENED AT RAILROAD CONSTR. AREA - WILL FILE AMENDED REPORT IF NOT MSHA JURISDICTION.)