Knee pain is very common, especially among athletes. About one third of doctor's visits for muscles and bone pain involve knees.
What are sudden (acute) injuries?
"Sudden injuries may be caused by a direct blow to the knee or from abnormal twisting, bending, or falling on the knee" ("Frequently Asked Questions").
What are overuse injuries?
"Overuse injuries occur with repetitive activities or repeated or prolonged pressure on the knee. Activities such as stair climbing, bicycle riding, jogging or jumping stress the joints and other tissues and can lead to irritation and inflammation" ("Frequently Asked Questions").
What causes runner's knee?
Runner's knee can be caused by overuse, direct trauma to the knee, misaligned knee or bones in the leg, problems with the feet or weak thigh muscles.
What causes an ACL injury?
If your knee joint is bent backward, twisted, or bent sideways, you can injure your ACL. An ACL injury is a tear in a knee ligament that joins the upper leg bone with the lower leg bone. This injury can range from mild to severe. A tear would be considered as a mild injury but a severe injury occurs when there is a tear in the ligament completely or when the ligament and part of the bone separate from the rest of the bone.