The knee is a hinge joint that is responsible for weight-bearing and movement. It consists of bones, meniscus, ligaments, and tendons. The knee is designed to fulfill various amounts of functions, including the following:
- Provide enough stability.
- Helps to lower and raise your body.
- Allows twisting of the leg.
- Makes walking much more efficient.
- Supports the body in an upright position without the need for muscles to function.
A bruise is skin discoloration from a skin or tissue injury. This injury damages blood vessels underneath the skin, causing them to leak. When blood pools right under the skin, it causes black, blue, purple, brown, or yellow discoloration. A bruised knee (also known as a knee contusion) is bruising caused by direct trauma to muscle, or bone located at the knee joint.
While most bruised knees aren’t serious, a very hard impact may result in intense pain and difficulty moving the leg. While bruising at the knee typically occurs following an impact injury, it may also occur following any kind of soft tissue damage. For instance, a knee sprain (torn ligament), or strain to a surrounding muscle or tendons (normally the hamstrings).
In some cases, experiencing a bruised knee can also lead to the development of a swollen knee. A swollen knee occurs when an excessive amount of fluid accumulates in or around your knee joint. Your doctor might refer to this condition as an effusion in your knee joint.
A swollen knee may be the result of similar causes to a bruised knee, such as trauma, overuse injuries, or an underlying disease or condition. In order to determine the cause of the swelling and bruising, your doctor may need to collect a sample of the fluid to test for infection, disease, or injury.