A knee contusion is an injury that results in bruising, swelling, and tenderness on or below the kneecap. Most contusions are relatively minor surface injuries, simply causing skin bruises due to broken blood vessels very near the surface of the knee. Symptoms of a mild knee contusion tend to go away within a week or two with simple home care. Intense pain and bruising may be indicative of a more severe muscle or bone contusion that should be evaluated by a physician. Depending on the seriousness of an injury, a person may have difficulty using his or her leg for several weeks or months.

Skin bruises occur when tiny blood vessels called capillaries are broken and allow blood to escape into cutaneous tissue. A mild knee contusion can result from falling, bumping into a door or table, or getting hit with a sports ball. A person may notice slight swelling and tenderness, but the injury does not normally impede the ability to use the leg. A bruise typically appears as dark blue or purple spot within about a day of the initial injury. The knee starts feeling better and the bruise becomes lighter over the course of several days.

A person can lessen the pain and healing time of a mild knee contusion by resting, icing, and elevating the joint. Over-the-counter anti-inflammatory drugs can be taken to further reduce swelling and pain. Intense physical activity should be avoided for a couple of weeks following an injury to give the knee sufficient time to recover. When bruising subsides and the joint feels better, a person can engage in light stretching exercises to regain flexibility.

A knee contusion that results in debilitating pain and swelling is generally considered a medical emergency. Deep contusions are most common in contact sports, car accidents, and hard impacts from falls. A person who suffers a serious knee injury should try to keep the leg immobilized until medical treatment is available. In the emergency room or doctor's office, a physician can take x-rays and conduct a physical examination to determine the extent of the injury.

Most contusions that affect bone, muscle, cartilage, or ligament tissue in the knee are treated in much the same way as skin bruises, though full recoveries can take several months. A doctor may prescribe high-strength pain relievers or anti-inflammatory drugs to take while resting and icing the leg. Some patients, especially athletes, enter physical therapy at some point in their recovery to rebuild strength and flexibility. Surgery may be necessary if a knee contusion is accompanied by a bone break or ligament tear.