The knee is one of the largest and most complex joints in the body. The healthy knee lets us walk, turn, squat without any pain. The natural knee consists of 3 bones: the thigh bone (femur), the shin bone (tibia) and the kneecap (patella). As well as bones, a network of muscles, ligaments, tendons, cartilage and other soft tissues in your knee all work together to provide your body with both stability and mobility.
Cartilage is a tough, very smooth material that protects bones and absorbs shock. There are two types of cartilage in your knee:
- Articular cartilage (stretchy) – it covers the end of the bones where the thigh bone and the shinbone meet – its smoothness allows pain free movement.
- Meniscal cartilage (thick and fibrous pads, called the meniscus). Menisci are like rubbery shock absorbers that help the knee withstand jolting forces, like when you are going down stairs or running.
Synovium is a thin layer of tissue that acts as a membrane to determine what can pass into and out of the joint space. It also produces synovial fluid (joint fluid), which lubricates knee motion. In the case of injury, the synovium can become inflamed, and secrete excess synovial fluid (a protective response). Over time, this inflammation can destroy some of your cartilage and even bone.
Ligaments connect one bone to another bone. They provide strength and stability to the knee joint from front to back, side to side, and from rotation. Each of the major ligaments is vulnerable to damage from different types of motion.
Tendons connect muscle to bone. Overuse can cause tendonitis, which produces local pain and tenderness. Tendons can also rupture.