The swelling seems to be getting worse, or you cannot walk following an injury. But like most complex systems, if you disrupt that harmony, the whole system can suddenly go haywire. When you severely injure an ankle, that once-quiet joint becomes a hotbed of activity, according to Gary M. Gordon, D.P.M., director of the Running and Walking Clinic at the University of Pennsylvania Sports Medicine Center in Philadelphia. Nerves, muscles and other tissues become aggravated. Vessels and capillaries tear, leaking blood.
More blood rushes to the area to begin the healing process.
Fluids accumulate faster than they can be removed, and you have swelling. All three can swell, hurt and leave an ugly bruise. Only a physician can properly diagnose which one you have. In addition to injury, there are a number of other possible causes for a swollen ankle. And all of them are fairly common.