The first metacarpal bone is the most massive, shortest, and widest among metacarpals. Overall, it is anatomically different from the rest of the metacarpals. Unlike other metacarpals, the first metacarpal does not articulate with adjacent metacarpals. It has only two articular surfaces.

The base of this bone is saddle-shaped and articulates with the trapezium, forming the first carpometacarpal joint. The saddle-shaped configuration of the joint allows thumb mobility.

Distally, the head of the first metacarpal articulates with the base of the proximal phalanx. The head of the first metacarpal is rounded but less spherical than it is for other metacarpals. It appears more flattened.

Overall, the first metacarpal bone has the following articular surfaces:

The first metacarpal serves as an attachment site for such muscles as the abductor pollicis longus, opponens pollicis, and first dorsal interosseous.

Additionally, a pair of sesamoid bones are usually found on the palmar aspect at the head of the first metacarpal bone. They are embedded in the tendons of the flexor pollicis brevis and adductor pollicis muscles.

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First metacarpal bone