Metacarpal 1 (right) — first metacarpal (thumb)

Function

The shortest, thickest and most mobile metacarpal. Its saddle joint with the trapezium allows opposition — rotating the thumb across the palm to meet every fingertip.

Landmarks

• Base
• Shaft
• Head (knuckle)

Articulations (joints)

• Trapezium
• Adjacent metacarpals (interosseous ligaments)
• Proximal phalanx of the thumb (metacarpophalangeal joint)

Clinical relevance

Bennett's fracture — an intra-articular first-metacarpal base fracture — destabilises thumb pinch; Rolando fractures shatter the base in a Y pattern.