Knee pain

Knee pain is incredibly common. It affects as many as a third of all teenagers and young adults in the UK at some time. Knee pain is a special problem for athletes -- over half of all athletes endure it every year.

Some of the most common reasons for knee pain are swollen or torn ligaments, meniscus (cartilage) tears and runner's knee. But the knee is a complex joint and there's plenty more that can go wrong.

Other conditions that cause knee pain are:

• Bone chips. Sometimes, a knee injury can break off fragments from the bone or cartilage. These pieces can get stuck in the joint, causing it to freeze up. You may also have pain and swelling.
• Bursitis. A bursa is a sac of fluid that cushions and protects your joints. There are several in different parts of your knee. Overuse, a fall, or repeated bending can irritate the bursa, causing pain and swelling. Two types of bursitis are called ''housemaid’s knee'' and ''clergyman's knee,'' since they are often caused by kneeling. A ''Baker's cyst'' -- a swelling behind the knee -- can also result from injuries and from conditions like arthritis.
• Iliotibial band syndrome. The iliotibial band is a piece of tough tissue that runs from your hip down to your shin. If it's irritated by overuse or other problems, it can become swollen and cause pain on the outside of the knee.
• Medial plica syndrome. The plica is a fold of tissue in the knee joint. When it gets irritated from overuse, swelling and knee pain can result.
• Osgood- Schlatter Disease. This condition causes a painful bump below the knee where a tendon from the kneecap connects to the shin. It's usually caused by overuse and irritation of the tendon. The pain may come and go over time. It's especially common in teenage boys and girls (13 and 14 years of age).
• Osteoarthritis. This condition is a frequent cause of knee pain in athletes and non-athletes alike who are over 60.
• Partially dislocated kneecap (or patellar subluxation). In this condition, the kneecap slides out of position, causing knee pain and swelling. It's often the result of a physical defect in your legs, rather than an injury. It's particularly common in teenage girls.
• Tendonitis, or swelling of the tendons. Tendons are tough bands of tissue that connect your bones and muscles. Overuse can make the tendons inflamed and sore. One type of knee tendonitis is called ''jumper's knee.''

If an old knee injury was not properly treated, it may keep causing occasional, or constant, knee pain.

What does a knee injury feel like?

Of course, the symptoms vary depending on your specific knee injury, but things to look out for are:

• Pain, often when bending or straightening the knee
• Swelling

If you have either of these symptoms, seek medical advice. Together, you can work out the cause. To diagnose what's causing your knee pain, your doctor will need to do a thorough examination. You may need to go to hospital for X-rays, MRIs (magnetic resonance imaging), or MR arthrogram -- a special type of MRI in which a dye is injected into the knee to see more detail of the joint.