<Li> extension: straightening limbs at a joint </Li> <Li> flexion: bending the limbs at a joint </Li> <Li> rotation: a circular movement around a fixed point </Li> <P> The joint space equals the distance between the involved bones of the joint . A joint space narrowing is a sign of either (or both) osteoarthritis and inflammatory degeneration . The normal joint space is at least 2 mm in the hip (at the superior acetabulum), at least 3 mm in the knee, and 4--5 mm in the shoulder joint . For the temporomandibular joint, a joint space of between 1.5 and 4 mm is regarded as normal . Joint space narrowing is therefore a component of several radiographic classifications of osteoarthritis . </P>

Identify the type of synovial joint at the proximal end of the tibia