EE was walking in parking lot,tripped on gravel falling on left knee.EE reported falling awkward and twisted knee.EE worked until 4am at which time pain and swelling hindered walking.EE refused ambulance transportation.EE RTW on RD on 3/12/10. On 3/14/10 mine mgt. decided EE was not to RTW until released to full duty. EE quit on own terms on 3/21/2010.