Knee pain

Sudden pain in one of the knees is usually the result of overusing the knee or injuring it. In many cases, you don’t need to see your GP.

The knee joint is particularly vulnerable to damage and pain because it takes the full weight of your body and any extra force when you run or jump.

You’re more likely to experience knee pain as you get older, and people who are overweight or do lots of sports have a higher risk of damaging their knees. Some sports that involve a lot of turning, such as football, netball and skiing, carry a particularly high risk of knee injuries.

Common causes of knee pain
Common causes of knee pain include:

• sprains and strains
  anterior knee pain (pain around the kneecap)
  menisci or cartilage damage
  osteoarthritis
  tendonitis
  bursitis (housemaid’s knee)
  torn ligaments or tendons
  bleeding into the joint
  Osgood-Schlatter’s disease
  gout
  septic arthritis (infected knee joint)

Source: NHS UK

http://www.nhs.uk/conditions/knee-pain/Pages/Introduction.aspx