A sprain can result from a fall, a sudden twist, or a blow to the body that forces a joint out of its normal position and stretches or tears the ligament supporting that joint. Typically, sprains occur when people fall and land on an outstretched arm, slide into a baseball base, land on the side of their foot, or twist a knee with the foot planted firmly on the ground.

Although sprains can occur in both the upper and lower parts of the body, the most common site is the ankle. The ankle joint is supported by several ligaments on the inside and outside of the ankle. Most ankle sprains happen when the foot turns inward as a person runs, turns, falls, or lands on the ankle after a jump. The knee is another common site for a sprain. A blow to the knee or a fall is often the cause; sudden twisting can also result in a sprain.

Sprains frequently occur at the wrist, typically when people fall and land on an outstretched hand. A sprain to the thumb is common in skiing and other sports. This injury often occurs when a ligament near the base of the thumb is torn.