The knee is one of the largest and most complex joints in the body. The knee joins the thigh bone (femur) to the shin bone (tibia). The smaller bone that runs alongside the tibia (the fibula) and the kneecap (patella) are the other bones that make the knee joint.
Tendons connect the knee bones to the leg muscles that move the knee joint. The anterior cruciate ligament prevents the femur from sliding backward on the tibia (or the tibia sliding forward on the femur). The posterior cruciate ligament prevents the femur from sliding forward on the tibia (or the tibia from sliding backward on the femur). The medial and lateral collateral ligaments prevent the femur from sliding side to side. Two C-shaped pieces of cartilage called the medial and lateral menisci act as shock absorbers between the femur and tibia. Numerous bursae, or fluid-filled sacs, help the knee move smoothly.
Your knee joints serve a vital role holding up your bodyweight and are put through even more pressure when you walk, run or jump. Knee pain is very common, both from sport injuries and the wear and tear of day-to-day life.
Knee pain can come from injuries including sprains, swollen or torn ligaments (anterior cruciate ligament or ACL), meniscus or cartilage tears and runner's knee.
Sports injuries tend to affect one knee at a time. Pain in both knees is more common with arthritis, osteoarthritis, gout or pseudogout, usually later in life.
Conditions that cause knee pain
Tendonitis. This is an overuse injury causing swelling of the tendons, the bands of tissue that connect your bones and muscles. This is sometimes called 'jumper's knee' as it is common in sports involving jumping, such as basketball.
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.
Housemaid's knee or bursitisis caused by kneeling for long periods of time or repetitive knee movements. Fluid builds up in the bursa, the sac of fluid that cushions the knee joints. Swelling behind the knee is called a 'Baker's cyst' and may be caused by injuries or arthritis.
Bleeding in the knee joint. This injury is also called haemarthrosis and affects blood vessels around the knee ligaments causing the knee to feel warm, stiff, bruised and swollen. This may require hospital treatment in severe cases.
Osgood-Schlatter Disease. This overuse condition is common in teenagers playing sport and causes swelling and tenderness over the bony bump just below the knee.