The knee is a synovial knee joint that allows flexion, extension and also a slight ability to rotate medially and laterally, being able to move on two planes, being known as a modified hinge joint. The main features of a synovial joint are the articulating cartilage, the joint capsule, the joint cavity, the bursae and the ligaments. The joint capsule is composed by the synovium and a fibrous capsule, keeping the synovial fluid that fills the joint cavity inside the joint. The most common injuries or diseases that affects this complex biomechanical system are arthritis, bursitis and dislocations. In fact, the synovium the central area of pathology in a number of inflammatory joint diseases, such as rheumatoid arthritis (RA) and spondyloarthritis (SpA).