- There are eight carpal bones of the wrist, arranged in two rows of four.
- proximal row (radial to ulnar) : scaphoid, lunate, triquetrum, pisiform
- distal row (radial to ulnar) : trapezius, trapezoid, capitate, hamate
- The carpals articular with:
- the radius primarily, but also with the ulna proximally, forming the wrist joint (radiocarpal, ulnocarpal joints).
- the metacarpals distally, forming the carpometacarpal joints.
- Specifically, the joint between the trapezius and the metacarpal of the thumb is the 1st carpometacarpal joint, aka the famous saddle joint of the thumb.
- The walls of the carpal tunnel are formed by the tubercles of the scaphoid and trapezium laterally and the pisiform and the hook of the hamate medially.
NOTES:
- The piriform is a sesamoid (round) bone that formed later. That is why there are seven tarsal bones but eight carpal bones.
- There is a well-known mnemonic for learning the carpals: Some Lovers Try Positions That They Can’t Handle = Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate.