Basic Knee Anatomy

The knee is the largest joint in the body. The knee joint is made up of the femur, tibia and patella (knee-cap). All these bones are lined with articular surface cartilage. This articular cartilage acts like a shock absorber and allows a smooth low friction surface for the knee to move on.

Between the tibia and femur lie two floating wedge-shaped shock-absorbing cartilages called menisci. The medial (inner) meniscus and the lateral (outer) meniscus are attached at the front and back ends and around where they attach to the joint capsule, but are still quite mobile, especially the lateral one. The menisci spread the load more evenly between the rounded femoral surface and the flatter tibial surface. The knee is stabilised by ligaments that are both in and outside the joint. The medial and lateral collateral ligaments support the knee from excessive side-to-side movement. The internal ligaments are the anterior and posterior cruciate ligaments which control the fore and aft movement of the tibia on the femur. If the posterior cruciate (PCL) is lax, the tibia drops back and there is more pressure on the knee cap, but not usually a feeling of instability. But when the anterior cruciate (ACL) is torn, it can feel like the knee can just gives way with certain movements.

The knee joint is surrounded by a capsule, and that is lined with a thin layer of synovium, which produces synovial fluid which is both nourishing and lubricating to the joint surfaces, to help with smooth motion. The thigh muscles are important secondary knee stabilisers, especially for the patella, to keep it tracking properly  in the trochlea groove on the femur.