Knee pain and injuries are the most common of all joint-related problems. Knee pain can affect people at any age. It may start suddenly after an injury or begin as mild discomfort, depending on the cause.

Signs and symptoms may include:

• Swelling or redness and warmth
• Weak or unstable knee
• Difficulty straightening your knee
• Popping or clicking sounds
• The knee buckles or locks

Knee pain can be caused by injury to the tissue and bones of the joint, or by arthritis, the gradual deterioration of cartilage in the joint.

Risk factors for knee pain include:

• Overweight – Extra weight adds stress on your knee joint and speeds the breakdown of cartilage in the joint.
• Weak or inflexible muscles – Strong muscles help stabilize your knee; flexible muscles give you greater mobility and range of motion.
• Some jobs or sports – Work that puts repetitive stress on your knee, such as construction work, can increase your risk. Sports such as basketball, skiing, and even running, can twist or pound your knees.

Common causes of knee pain include:

• Arthritis – Osteoarthritis affects 24% of adults, usually middle-aged or older people. It occurs as cartilage in the knee joint gradually wears away, and typically gets worse with time. Less common forms of arthritis in the knee include rheumatoid arthritis, an auto immune disease that causes inflammation of the joint. Gout, the buildup of uric acid crystals, can occur in the knee. Septic arthritis, caused by infection in the knee, comes on suddenly and should be treated by a doctor right away.
• Torn meniscus – Menisci are pads of cartilage that act as shock absorbers in the knee. A torn meniscus is one of the most common knee injuries.
• ACL injury – Your ACL is a ligament that connects your thigh to your shin. It’s the ligament most often injured in your knee , and usually occurs when playing sports in which you change direction suddenly, such as soccer or basketball.
• Bursitis – Bursae are small sacs of fluid that cushion the outside of your knee joint. They can become inflamed by an injury.
• Tendonitis – Tendons are thick tissue that attach your muscles to bone. The patellar tendon in your knee can become inflamed if injured.
• IT band syndrome – The iliotibial band, tissue that extends from the outside of the knee to the outside of the hip, can become tight and rub against the thighbone. This is more common among cyclists and distance runners.
• Fractured or dislocated knee – The kneecap can be broken or dislocated in a fall or accident.
• Hip or foot pain – People with hip or foot pain sometimes change their gait – the way they walk – to favor the painful joint. The change can put more stress on the knee.

Your doctor will ask questions to get your medical history, and do a physical exam to check for swelling, bruising, tenderness and mobility.

Your doctor may also recommend other tests, including: 

• X-ray – X-rays use electromagnetic waves to take pictures of the bones in your knee. They can detect fractures and deterioration of the joint. ·
• MRI – Magnetic resonance imaging uses a powerful magnet and radio waves to create 3D images of the tissue inside your knee. MRIs help find tears to soft tissues such as tendons, ligaments, muscles and cartilage.
• CT scan – Computerized tomography combines multiple X-rays and computer technology to create cross-sectional images of your knee. It can make images of the bones and muscles in the knee.
• Arthroscopy – This minimally invasive procedure inserts a tiny, lighted tube into the knee joint. Pictures from inside the joint are projected onto a screen, helping doctors spot arthritic changes and bone diseases or tumors.
• Ultrasound – Sound waves produce images of the soft tissue in and around your knee, checking for specific problems.
• Radionuclide bone scan – A tiny amount of radioactive material is injected into your bloodstream and tracked by a scanner. The test can show blood flow to the bone and the activity of cells within the bone.
• Lab tests – Blood tests or fluid from your knee joint may be analyzed to check for infection.

Treatment depends on the cause of your knee pain.

• Ice and rest – Mild knee pain can sometimes be treated at home. Apply ice wrapped in a towel. Keep your knee elevated. Rest and avoid putting weight on your knee.
• Medications – Anti-inflammatory medicine such as ibuprofen (Motrin) or naproxen (Aleve) can help ease swelling. Acetaminophen (Tylenol) can help relieve pain.
• Physical therapy – Your knee becomes more stable when the muscles around it are stronger. Physical therapy can help you learn safe and effective exercises to strengthen those muscles.
• Injections – Corticosteroid shots may help reduce inflammation and pain for a few months.
• Arthroscopic surgery – Long, narrow tools fitted with a tiny camera are inserted into your knee joint. Using these tools, surgeons can reconstruct torn ligaments, repair damaged cartilage and remove loose bits of cartilage or bone from your joint.
• Knee replacement surgery – The surgeon replaces damaged bone and cartilage in your knee with an artificial joint made of metal alloys and medical grade polyethylene (plastic). Most knee replacements last at least 15 to 20 years.
• Osteotomy – The surgeon cuts away bone to reshape or realign the bones that meet at the knee joint. This may delay the need for knee replacement surgery in younger people.