The knee is the largest joint in the body. It is a specialised hinge joint made up of four main things: bone, cartilage, ligaments and tendons. The main movement that occurs in the knee joint is flexion and extension. It does however allow for a small amount of rotation and gliding on the surfaces.
There are three main bone structures that make up the knee:
- Femur (thighbone) – the longest and strongest bone in the body, the femur runs from the hip to the knee.
- Tibia (shinbone) – the larger of the lower leg bones that runs from the knee to the ankle
- Patella (kneecap) – a round shaped piece of bone that sits over the front of the knee. It helps the muscles to straighten the knee joint from a bent position.
There are two types of cartilage in the knee joint. Both are essential for the normal function of the joint.
- The articular cartilage is the smooth white tissue that covers the ends of the femur, tibia and the back surface of the patella to form the joint. Articular cartilage creates a smooth surface for the bones to glide over one another without friction. It also acts as a shock absorber in high impact activities.
- The meniscus is a soft wedge shaped disc of cushioning cartilage that helps with the stability of the knee joint. Its tough and rubbery structure also helps to cushion the knee joint. There are two menisci (medial and lateral) within each side of the knee joint.
Are bands of fibrous tissue that hold the knee joint together and increase its stability. There are two groups of ligaments that make up the knee joint.
- The collateral ligaments are located on either of the knee joint. These are called the medial collateral ligament (MCL) on the inner side of the knee and the lateral collateral ligament (LCL) on the outer side of the knee. These control sideways motion of the knee and brace it against unusual movement.
- The cruciate ligaments are found inside the knee joint. They cross each other to form and “X” in the centre of the knee. The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) prevent the femur and tibia from sliding backwards and forwards on each other .
Muscles are connected to bones by tendons. Large muscle groups, including the quadriceps and hamstrings muscles, cross over the knee joint and help to power its movement. These muscle groups are also essential for the stability of the joint.
Synovium – Forms the lining of the joint and produces the fluid which lubricates the joint.A thin fluid membrane called synovium exists between the femur, tibia and behind the patella to lubricate the joint and add additional cushioning to support smooth movement
Blood vessels and Nerves – Major blood vessels and nerves pass through the knee joint to aid supply of the lower limbs with blood and sensory and motor function.