Bones of the Human Wrist
The human wrist contains eight carpal bones arranged in two rows: the proximal row consists of the scaphoid, lunate, triquetrum, and pisiform, while the distal row includes the trapezium, trapezoid, capitate, and hamate. 1, 2
Proximal Carpal Row (Radial to Ulnar)
- Scaphoid: The largest bone in the proximal row that bridges both carpal rows and is critical for wrist stability 1, 3
- Lunate: Positioned centrally in the proximal row, articulating with the radius 1, 2
- Triquetrum: Located on the ulnar side of the proximal row 1, 2
- Pisiform: A sesamoid bone that sits within the flexor carpi ulnaris tendon, articulating only with the triquetrum 1, 2
Distal Carpal Row (Radial to Ulnar)
- Trapezium: Articulates with the first metacarpal (thumb) 1, 2
- Trapezoid: Positioned between the trapezium and capitate 1, 2
- Capitate: The largest carpal bone, serving as the central keystone of the wrist 1, 2
- Hamate: Located on the ulnar side of the distal row, characterized by its hook-like process 1, 2
Functional Organization
- The proximal carpal row functions as an intercalated segment or "flexible place-holder" between the radius/ulna and the distal carpal row, allowing adaptive motion 4
- The distal carpal row moves more rigidly as a unit (less than 3 degrees of relative motion between bones) and articulates with the five metacarpal bases 3
- These eight carpal bones, combined with the distal radius and ulna, create the complex wrist joint with 42 degrees of freedom when considering individual bone movements 3, 5