Employee stated that when he dismounted from #42 jeep at 3 right switch he felt pain in his right knee. He stated that he then walked on it for a period of time and it appeared to feel better. He then went to 37 block on 1 north and was carrying one joint of 4"" pvc pipe thru a crosscut. He again felt pain in his knee. felt to the mine floor and fractured his right ankle.