Swelling of the left foot in the elderly commonly occurs for the following reasons: I. Left foot sprain: The muscles of the lower limbs of elderly patients continue to weaken with age and their strength decreases, so the protective effect can be significantly diminished. When going down the steps, the left foot is easily sprained, and the patient can experience local swelling, pain and restricted activities. Then local thrombosis will easily occur, which will affect the blood circulation at the end of the limb, leading to swelling of the left foot, and the patient will also be accompanied by painful performance of the leg.