Knee pain can be related to overuse where small stresses are placed a large number of times on knee without allowing adequate recovery, for example running too much too soon, or excessive jumping. Or knee pain can be acute where the injury is caused by an impact or twisting of the knee such as an anterior cruciate ligament injury. An overuse injury can also be considered to be acute if it is painful or inflammed.

Knee pain is a common reason that people visit their doctors' offices or the emergency room. Often, knee pain is the result of an injury, such as a ruptured ligament or torn cartilage. But some medical conditions can also bring you to your knees, including arthritis, gout and infections.
The knee joint is surrounded by a joint capsule with ligaments strapping the inside and outside of the joint (collateral ligaments) as well as crossing within the joint (circulate ligaments). These ligaments provide stability and strength to the knee joint.

Symptoms of Knee Pain

Loose body: Sometimes injury or degeneration of bone or cartilage can cause a piece of bone or cartilage to break off and float in the joint space. This may not create any problems unless the loose body interferes with knee joint movement — the effect is something like a pencil caught in a door hinge — leading to pain and a locked joint.
Septic arthritis: Sometimes your knee joint can become infected, leading to swelling, pain and redness. Septic arthritis often occurs with a fever.

Bursitis: The most common bursa affected around the joint is just above the kneecap. This is most common in people who kneel for work, such as gardeners or carpetlayers.

Swelling of the knee is common with several different knee problems. When there is swelling immediately after an injury (within an hour), the most common causes are an injury to the anterior cruciate ligament or a fracture of the top of the shin bone. When swelling develops gradually over hours to days, the injury is more likely a tear of the meniscus or a ligament sprain.

Treatment for Knee Pain

Rest: The first treatment for most common conditions that cause knee pain is to rest the joint, and allow the acute inflammation to subside. Often this is the only step needed to relieve knee pain. If the symptoms are severe, crutches may be helpful as well.

Protection: The best way to protect your knee from further damage depends on the type and severity of your injury. For most minor injuries, a compression wrap is usually sufficient. More serious injuries, such as a torn ACL or high-grade collateral ligament sprain usually require crutches and sometimes also a brace to help stabilize the joint with weight bearing.
Exercises considered better for the knees include small (not deep) knee bends and straightening motions - done while in supination with most weight on the outside of the foot.

Most knee conditions respond to a combination of non-invasive treatments such as applying heat or cold, temporarily restraining from activities that aggravate pain, and medications that target pain and inflammation. Exercises to strengthen the muscles that support the knee help reduce stress on the knee joint and prevent re-injury.
Knee joint replacement: The knee is a complex joint, which is made up of the distal end of the femur (the femoral condyles), and the proximal end of the tibia (the tibial plateau). The femoral condyles usually glide smoothly on the tibial plateau, allowing for smooth, painless motion of the lower leg. (Illustrated).