Why does the knee or ankle swell up if injured?

Knees and ankles - the swelling of an injured joint, like a knee or an ankle, is caused by the multiplication of normal cells to cushion the affected part. This sudden increase is called hyperplasia. There is also a certain amount of internal bleeding as a result of the injury. Swellings are divided into two main groups, false tumours and true tumours. The inflammatory swellings that appear after joint injuries belong to the first group, which includes bruises, black eyes, sprains, fractures and infectious swellings such as boils and abscesses. Swollen joints can be eased by the application of cold compresses, or pads, and ice packs. Firm bandages are used to give support. True tumours or swellings are composed of masses of tissue developed frombody cells which already exist. They have a tendency to keep growing. Some of these tumours have normal cells and are said to be benign or harmless. In others the cells are slightly different from their parents and the tumours are generally malignant.