A knee sprain usually occurs due to unnatural movements during physical activity. Sudden turns or pivoting can cause injury to your ligaments. Knee sprains are common in sports with lots of running, jumping, and turning, such as in football, basketball, and skiing.
Direct hits to the knee can also cause knee sprains. The most obvious example is in contact sports, when there may be physical contact between two players or the ground. An incident such as falling or a car accident can also cause knee sprains.
Many patients suffering from knee sprains hear a popping noise at the time of injury. Pain and tenderness in the knee accompanied by stiffness and swelling are common signs of a knee sprain. Some patients may also experience bruising and instability when walking. In more severe cases, the patient may have trouble bearing weight on the affected leg.