The wrist is a highly mobile and complex region that serves as the transition point between the forearm and the hand. This area allows for the precise movements that make human hands functional. Anatomically, the wrist is not a single joint, but a collection of articulations. The primary joint responsible for connecting the forearm to the hand has a specific technical name reflecting the bones involved.
The Formal Name: The Radiocarpal Joint
The main articulation commonly referred to as the wrist joint is formally known as the radiocarpal joint. This name is a precise anatomical description derived from the two main groups of bones that meet here. The term “radio” refers to the radius, the larger forearm bone on the thumb side of the arm. “Carpal” refers to the carpus, the collective term for the eight small bones of the wrist.
The radiocarpal joint is categorized as a synovial joint. It is enclosed by a capsule and contains lubricating fluid to reduce friction during movement. This joint is the primary structure enabling the hand to move relative to the forearm.
The Bony Structure of the Wrist
The radiocarpal joint is formed by the concave surface of the distal end of the radius articulating with the convex surfaces of three bones from the proximal row of the carpus. The radius, situated on the thumb side of the forearm, bears the majority of the force transmitted from the hand. The opposing surface consists of the scaphoid, lunate, and triquetrum bones.
The ulna, the other bone in the forearm, does not directly articulate with the carpal bones. Instead, the Triangular Fibrocartilage Complex (TFCC) intervenes between the ulna’s distal end and the carpus. The TFCC acts as a cushion and stabilizer for the wrist. It ensures the ulna contributes to forearm rotation without directly participating in the primary joint articulation.
Range of Motion and Joint Classification
The radiocarpal joint is classified as an ellipsoidal, or condyloid, synovial joint. This classification means the joint allows motion along two primary axes. The movements enabled by this joint are flexion and extension, which involve bending the hand forward and backward.
The joint also permits side-to-side movements known as radial deviation and ulnar deviation. Radial deviation moves the hand toward the thumb side, while ulnar deviation moves the hand toward the pinky side. The combination of these four movements allows for circumduction, a circular motion of the hand. Full wrist motion requires the coordinated movement of the radiocarpal joint along with the adjacent midcarpal joints.