The wrist is the connection between the forearm and the hand. The forearm is composed of two bones, the radius and the ulna. At the end of these two bones are the joint surfaces of the wrist. These are termed the distal radius and distal ulna. These two bones are connected at this end and allow the wrist and forearm to rotate palm up and palm down. This is termed supination and pronation. At the wrist the radius and ulna are connected and stabilized by the TFCC (triangular fibrocartilage complex). The ulna is usually slightly shorter than the radius however, at times the ulna can be longer than the radius. This is called positive ulnar variance. The distal radius and the distal ulna/TFCC form a joint with the smaller bones of the wrist (carpal bones). When weight is transferred from the carpal bones to the wrist, about 80% of the force is usually transmitted through the distal radius and about 20% is transmitted through the TFCC/distal ulna.
The carpal bones include the scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate and hamate. These are aligned in two transverse rows and connect the forearm to the hand and fingers. These smaller carpal bones allow flexion, extension and deviation of the wrist as well as motion of the thumb.