An injury to either or both knees causing pain and/or disability.

The legs, especially the knees, are the most injury-prone parts of the body. Knee injuries are the leading cause of long-term disability among athletes.

Although most commonly due to sport, anyone can hurt their knees if they make an awkward movement or give the knee a hard blow. Some women may be especially susceptible because their wider pelvis tends to make them knock-kneed. Besides the knock-kneed, those prone to knee problems...