Torn cartilage

The meniscus is a crescent-shaped piece of cartilage (tough, fibrous tissue) that cushions the spot where bones meet in your knee. Sometimes a meniscus can tear after a sudden twist, or following repeated squatting. The result is pain and swelling, occasionally with painful clicking.

Torn ligament

A ligament (soft fibrous tissue that helps support your knee) can tear following a fall, twist, or blow. The result is swelling and a feeling of instability, a "trick" knee.

Patella problems

Your patella, better known as your kneecap, can suffer damage as a result of aging, overuse, or direct injury. Usually, there is minimal swelling but lots of pain in the front of the knee especially when using stairs. It is a very common condition.