The proximal surface of the trapezium combines with the trapezoid to form a concave surface for articulation with the convex distal articular surface of the scaphoid. The distal end of the trapezium is a sellar surface that articulates with the first metacarpal. This surface is convex. The large medial surface is concave for articulation with the trapezoid. The proximal surface is slightly concave for the scaphoid articulation.