Employee was walking on surface when he felt a ""pop"" in his R knee.He didn't fall/trip-just was walking.Since then,he has missed no days,but still had pain in his knee.He went to Dr. & surgery was done on 11/10/10.(not related to SMC, he had a previous knee surgery-now because of the ""pop"" in his knee,this hardware is being removed) His 1st shift missed is 11/9/10.