Pain in just one joint

Knee pain

The knee joint is probably the most frequently damaged jointand is particularly vulnerableas it takes the full weight of your body.

However, knee pain isn't always a joint problem. Learn about the most common causes of knee pain and what you should do.

The most common and more unusual causes of pain ina singlejoint are described below.

Inflammation of the joint lining

If you've injured the joint recently and it suddenly becomes painful again, thethin layer of tissue lining the joints and tendons may be inflamed a condition calledtraumatic synovitis. It usually doesn't cause any redness or heat.

You should be able to manage injury-related swelling at homewith anti-inflammatories , an icepack andrest.

Gout or pseudogout

If the skin over thejoint is hot and red, and the pain comes in repeated attacks, the cause is likely to be either gout or pseudogout.

Both conditions are types of arthritis.

Gout usually affects the joint of the big toe first, before affecting other joints. It's important to correctly diagnose gout, as treatmentwill prevent future attacks of joint pain and disability.

Pseudogout is a similar condition to gout, but usuallyaffects the knee joint first.

See your GP ifyou think you have either condition.

Damage to the cartilageat the back of the kneecap

Knee pain that feels worse when going up or down stairs could be a sign of a damaged kneecapa condition calledchondromalacia patellae.This shouldn't cause any redness or heat around the knee.

The cause isn't really understood, but it can be linked to overuse of the knee.

You can treat this problemyourselfwith anti-inflammatories , an icepack andrest.

Bleeding into the joint space

If you've recently had an injury to the knee joint, such as a torn ligament or knee fracture,it maycause bleeding into the joint spaces. This is known as haemarthrosis.

This is more likely to happen to people on anticoagulants , such as warfarin .

Signs of haemarthrosis are:

• swelling of the knee
• warmth
• stiffness and bruising, which occur soon after the injury

You should go to hospital immediately for treatment if you have a very swollen knee.

Less common causes

Sudden pain in a joint is less commonly caused by:

• a fracture read about a broken arm or wrist , broken leg , broken ankle or hip fracture
• reactive arthritis which usually develops after an infection andtends to affect young adults
• psoriatic arthritis a type of arthritis that affects up to one in five people with psoriasis
• rheumatoid arthritis which can start in just one joint, with the paincoming and going
• Osgood-Schlatter's disease swelling and tenderness over the bony bump just below the kneecap

Rarely, the cause may be:

• septic arthritis a serious condition that causes a painful, hot, swollen joint that you won't be able to move(sometimes withfever)see your GP urgently or go to A&E
• haemophilia an inherited condition that affects the blood's ability to clot
• atropical infection
• cancer
• crumbling of the bone (avascular necrosis) caused bya lack of blood supply
• repeated dislocation of the joint