A clinical phenomenon is that on the day of a broken foot it is not very painful, but as time goes on, the traumatized area becomes more and more painful on the second and third day, mainly triggered by swelling. The swelling of the ankle joint is not obvious when it is first injured, so the stimulation and compression of its nociceptive cells are not obvious, and the pain will naturally be milder. However, with the gradual edema and increased exudation of intertissue fluid after the injury, the soft tissue damage in the ankle joint will become increasingly worse. As the swelling increases, the pressure on the skin nociceptors of the ankle joint will gradually increase, resulting in increased pain.