The Carpo-Metacarpal Joints, between the five metatarsal bones and the distal row of carpal bones; the first metatarsal bone articulates with the trapezium, and the four inner metatarsals articulate with the other three bones.

First Carpo-Metacarpal Joint, between the base of the first metacarpal bone and the distal surface of the trapezium. The articulating surfaces of the joint are saddle-shaped, so that movements occur round three axes.

Transverse - flexion and extension.

Antero-posterior - abduction and adduction (to middle line of hand).

Longitudinal - rotation.

Although this is not a ball-and-socket joint, a certain amount of circumduction is possible, and the movement of opposition-i.e. bringing the thumb right across the hand-is due to a combination of flexion, adduction, and rotation.

Ligaments

A capsule surrounds the joint which has strengthening bands in it, forming four ligaments.

The synovial membrane lines the joint, which is quite separate and distinct.