Which distal row carpal bone is the keystone that articulates with the base of the third metacarpal?

Which distal row carpal bone is the keystone that articulates with the base of the third metacarpal?

• A. Capitate
• B. Hamate
• C. Trapezoid
• D. Trapezium

Answer: (A)

The central idea is identifying the keystone bone of the distal row of carpal bones, which articulates with the base of the third metacarpal. The capitate sits in the middle of the distal carpal row and forms the direct articulation with the base of the third metacarpal, making it the main anchor or axis for that part of the hand. This central position explains why it’s considered the keystone: it stabilizes the distal row and coordinates movement by linking to the middle finger’s metacarpal. The other distal row bones connect to the bases of the other metacarpals—trapezium with the first, trapezoid with the second, and hamate with the fourth and fifth—so they don’t serve as the central articulating link for the third metacarpal.

The central idea is identifying the keystone bone of the distal row of carpal bones, which articulates with the base of the third metacarpal. The capitate sits in the middle of the distal carpal row and forms the direct articulation with the base of the third metacarpal, making it the main anchor or axis for that part of the hand. This central position explains why it’s considered the keystone: it stabilizes the distal row and coordinates movement by linking to the middle finger’s metacarpal. The other distal row bones connect to the bases of the other metacarpals—trapezium with the first, trapezoid with the second, and hamate with the fourth and fifth—so they don’t serve as the central articulating link for the third metacarpal.