A sprain is a stretch or tear in a ligament. Ligaments are bands of fibrous tissue that connect bones to bones at joints. A strain is also a stretch or tear, but it happens in a muscle or a tendon. Tendons link muscles to the bones.
A sprain is usually caused by the joint being forced suddenly outside its usual range of movement and the inelastic fibers are stretched through too great a range. For example, excessive inversion of the ankle can cause the lateral ankle ligaments, primarily the anterior talofibular ligament, to rupture. A severe sprain may look and feel like a break (fracture), and it can be difficult for health professionals to tell the difference between the two.
How Do Sprains Happen?
Sprains usually happen when a person falls, twists, or is hit in a way that forces the body out of its normal position.
The most common type of sprain is a sprained ankle. About 25,000 people sprain an ankle every day. Think of a runner who goes over a curb and catches their foot, twisting the ankle; or a baseball player who slides into a base and twists their knee.
Wrist and thumb sprains are also common, particularly in sports like skiing, where it’s not unusual to fall and land on an outstretched palm.
How Can You Tell the Difference?
The signs of most sprains or strains are very similar: pain and inflammation, and sometimes bruising, at the injured area. Depending on how bad the sprain or strain is, the pain may be mild, moderate, or severe.
The worse the sprain or strain, the harder it is to use the affected area. Someone with a mild ankle sprain may just favor that ankle slightly. A more severe ankle sprain may cause much more pain and make it tough or impossible to walk.