The EE was getting down from the roof bolter. As he stepped down, he miss judged how far it was to the floor and when his foot hit the floor, his knee buckled and he fell to the ground. He finished out his shift and worked the next day's shift. He then wanted to see a dr. On 4/9/08 he was seen by a doctor and released to light duty. MSHS restricted duty on 4/9/08.