Introduction
The knee is one of the most complex organs of the body. It consists of two joints: the tibio- femoral joint, which binds the femur (thigh bone) and the tibia (shin bone) (Fig. 1), and the patella-femoral joint, which links the kneecap (patella) to the femur. The fibula is a smaller bone that runs alongside tibia, and it also participates in overall joint stability.
Different ligaments (Fig. 2) join the knee bones and provide stability to the knee: they can either be intra articular (anterior cruciate ligament, posterior cruciate ligament, the transverse ligament and the menisco-femoral ligaments) or extra articular.
The articular capsule is an elastic and fibrous membrane, which surrounds and delimits the joint. The articular capsule contributes to maintain the contact of the joint structures and to ensure stability.