Climbed up on 777 Truck to check the oil and reported feeling a stretching sensation in his left knee when he began to kneel down to open the engine acess compartment door. He stated he did not slip, strain, or fall. He worked until 1/29/10 when he had arthroscopy w/menisectomy on his left knee. EE began missing work on 1/29/10 and became lost time reportable accident on this date.