Most people bruise their knees from time to time. The blood vessels under the skin are damaged, often resulting in some pain. However, if bruising occurs for no apparent reason and is accompanied by pain, it could be a symptom of a number of conditions.
A Baker's cyst is an accumulation of fluid at the back of the knee. This often causes swelling, some discomfort and stiffness, but these symptoms usually are not extreme. However, if the cyst ruptures, it can cause bruising and pain. The condition usually resolves itself without treatment; surgery is used only in extreme cases because of the risk of damaging blood vessels around the cyst.
Varicose veins are swollen, twisted and often painful. The valves in the affected veins cease to function properly, causing blood to pool. As a result, the veins swell and, in some cases, burst. Bruising can occur around a burst vein. Doctors sometimes recommend surgery to address the problem.
Knee sprains occur when the ligament that holds the joint together is over-stretched and damaged. This can cause bruising and pain around the knee as well as swelling and tenderness. Treatment often involves compressing the knee with a bandage, applying ice to the knee and resting the damaged leg. In severe cases, the patient might need to wear a brace.
A kneecap can slide out of place, becoming dislocated. A dislocated kneecap causes swelling and pain. If a section of the kneecap breaks off, it can become lodged in the muscles of the knee after the kneecap has been put back in place. This bone shard can cause bruising and pain, usually on the outside of the knee, where a dislocated kneecap usually slides. A bone shard must be surgically removed.
Consult your doctor if you experience random bruising around the knee accompanied by pain. The causes usually can be treated easily, but it is best to begin as quickly as possible.