What is a Sprain?

What Is the Difference Between a Sprain and a Strain?

A sprain is a stretch and/or tear of a ligament (a band of fibrous tissue that connects two or more bones at a joint). One or more ligaments can be injured at the same time. The severity of the injury will depend on the extent of injury (whether a tear is partial or complete) and the number of ligaments involved.

A strain is an injury to either a muscle or a tendon (fibrous cords of tissue that connect muscle to bone). Depending on the severity of the injury, a strain may be a simple overstretch of the muscle or tendon, or it can result from a partial or complete tear.

What Causes a Sprain?

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.

Where Do Sprains Usually Occur?

Although sprains can occur in both the upper and lower parts of the body, the most common site is the ankle. More than 25,000 individuals sprain an ankle each day in the United States.

The ankle joint is supported by several lateral (outside) ligaments and medial (inside) ligaments (see fig. 1). Most ankle sprains happen when the foot turns inward as a person runs, turns, falls, or lands on the ankle after a jump. This type of sprain is called an inversion injury. 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 (see fig. 2).

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 (the ulnar collateral ligament of the metacarpo-phalangeal joint) is torn (see fig. 3).