A miner slipped on snow, spraining the right knee. He finished the shift and worked the next shift, the 2008 workforce layoff date. After recall on 3/9/09, the miner performed regular duties, but discomfort / swelling continued. On 10/13/09, a doctor recommended surgery. The miner chose to work until 12/3/09. The surgery date was 12/4/09, the 2009 workforce layoff date.