May also be called: Bruise A contusion (kun-TOO-zhun), or bruise, of the knee is an injury to the skin and underlying tissue of the knee. More to Know A contusion, or bruise, forms when soft tissue in the body is crushed but the skin doesn't break. When this happens, blood from broken capillaries (small blood vessels) near the skin's surface may leak out under the skin. With no place to go, the blood gets trapped, often forming a red or purplish mark that hurts when you touch it. As a contusion heals, it may turn different colors, from red and purple to black and blue and then to green, yellow, and light brown before fading away. Keep in Mind Applying a cold compress to a contusion may help minimize swelling and bruising. Seek medical attention if a contusion doesn't heal or continues to be painful. All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts. Back to Articles Related Articles A to Z: Contusion (Bruise), Buttocks Learn more about contusions (bruises) of the buttocks. Read More A to Z: Contusion (Bruise), Hip Learn more about contusions (bruises) of the hip. Read More A to Z: Contusion (Bruise), Lower Leg Learn more about contusions (bruises) of the lower leg. Read More Word! Bruise When you bang a part of your body against something, your skin might turn different colors where you bumped it. Read More Medial Collateral Ligament (MCL) Injuries MCL injuries can happen in active and athletic kids, when excessive pressure is put on the knee joint, resulting in a torn ligament. Read More Bruises This article is all about bruises, including why they happen, how to make them go away faster, and why they turn all those funny colors. Read More Patellofemoral Pain Syndrome (Runner's Knee) Patellofemoral pain syndrome (or runner's knee) is the most common overuse injury among runners, but it can also happen to other athletes who do activities that require a lot of knee bending. Read More Jumper's Knee Jumper's knee is an overuse injury that happens when frequent jumping, running, and changing direction damages the patellar tendon. Read More Jumper's Knee Jumper's knee is an overuse injury that happens when frequent jumping, running, and changing direction damages the patellar tendon. Read More Knee Injuries Healthy knees are needed for many activities and sports and getting hurt can mean some time sitting on the sidelines. Read More Medial Collateral Ligament (MCL) Injuries MCL injuries happen when excessive pressure is put on the knee joint, causing a torn ligament. Read More Sports and Exercise Safety Playing hard doesn't have to mean getting hurt. The best way to ensure a long and injury-free athletic career is to play it safe from the start. Find out how. Read More Preventing Children's Sports Injuries Participation in sports can teach kids sportsmanship and discipline. But sports also carry the potential for injury. Here's how to protect your kids. Read More Knee Injuries Knee injuries are common among young athletes. Learn about causes, treatments, and prevention. Read More What's a Bruise? Have you ever had a bruise that turned a bunch of different colors before it went away? Find out why in this article for kids. Read More Anterior Cruciate Ligament (ACL) Tears ACL injuries can happen in active and athletic kids when excessive pressure is put on the knee joint, resulting in a torn ligament. Read More Anterior Cruciate Ligament (ACL) Tears ACL injuries can happen in active and athletic kids when excessive pressure is put on the knee joint, resulting in a torn ligament. Read More Meniscus Tears The key to healing meniscus tears is not to get back into play too quickly. Find out what meniscus tears are and how to treat them. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.