The employee was assisting in the removal of a wheel unit from a battery coal hauler. The unit was suspended on the forks of a mini-trak by a chain. The wheel unit rotated striking the employee's right knee. The accident occurred on 1-8-08. The EE did not have trouble with the injury until 1-13-08. He was seen by Dr. on 1-14-08. Same knee operated on in 2003, different reason.