While walking, injured his knee on the I-slope. Sent for x-ray determining strain of ligaments in left knee. Returned to work next scheduled shift and worked until MRI app 8/10. Worked on and off complaining going to the doctor several times. On 9/20/09 took additional MRI and then again on 9/30/09. Received results 10/5/09, determined it requires outpatient surgery 10/14.