The injury can be either an overstretching or a tear of one or more ligaments. Ligaments are tough bands of tissue that hold two bones together. How bad a sprain is depends on whether the ligament is torn completely or just partially. Also, the more ligaments involved, the more severe the injury. Most sprains are minor injuries.

Like a sprain, a strain involves an overstretch or a complete or partial tear, but of a muscle or tendon instead of a ligament. Tendons are similar to ligaments in that they are tough bands of tissue, but they attach a muscle to a bone instead of holding two bones together. Like sprains, most strains are minor injuries.

The most common site is the ankle. In fact, ankle sprains are the most common injury in the United States. About 1 million ankle injuries occur each year, and 85 percent of them are sprains. An ankle sprain most frequently occurs 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.

A sprain can also occur when a person falls and lands on an outstretched arm, or twists the knee when the foot is already planted on the ground. In sports, sliding into base or getting a blow to the body that forces a joint out of its normal position can also result in a sprain. Any event that forces a joint from its normal position can overstretch or tear a ligament.

This does not happen in all cases, however. Usual symptoms of a sprain include pain, swelling and bruising at the joint. You may not be able to move the joint or it may be extremely painful to move it. The symptoms vary in intensity, depending on the severity of the sprain.

Other times to see your health care provider for a sprain: the injured joint is tender to touch; the injured area looks crooked or has bumps not visible on an uninjured joint; your leg buckles when you try to use your injured knee or ankle; the injured area is numb; or the injured area has been injured previously.

Another common site is the hamstring muscle, at the back of the thigh. People who play contact sports such as soccer, football or hockey are at risk for strains. Hand and forearm strains are more common among people who play tennis, row or golf. Elbow strains can occur if you play racquet sports. Overuse of a joint can result in a chronic strain. For a chronic strain, the damage accumulates slowly, rather than all at once as in a fall or a blow to the joint.

Other symptoms include pain and muscle weakness. At the site of the injury, there may be swelling, cramping or inflammation. A severe strain involving a muscle or tendon tear can be very painful and disabling.

You should follow the RICE (Rest, Ice, Compression, Elevation) treatment for the first one to two days after the injury: Rest the injured joint, apply an icepack for 20 minutes four to eight times a day, wrap the joint with a compression bandage and elevate it above the level of your heart. Your health care provider may recommend a non-steroidal anti-inflammatory medication such as ibuprofen to help reduce pain and swelling. A moderate to severe sprain or strain may need a cast or brace to hold the joint still while it heals. A severe sprain or strain may require surgery to repair the tear. How long it takes a sprain or strain to heal depends on how the severity of the injury. A moderate ankle sprain might need up to six weeks to heal; a severe sprain might need a year.

Other ways to prevent sprains and strains include maintaining a healthy weight; avoiding falls by keeping walkways in and around your home clear of clutter and by using sand or salt on icy patches in the winter; and wearing protective equipment when a playing a sport that puts you at risk for a sprain or strain.