Wrist and Hand; structure, joints and function

STRUCTURE AND FUNCTION OF THE WRIST AND HAND

The bones of the wrist consist of the distal radius, scaphoid

(S), lunate (L), triquetrum (Tri), pisiform (P), trapezium

(Tm), trapezoid (Tz), capitate (C), and hamate (H). Five

metacarpals and 14 phalanges make up the hand and the

five digits.

Wrist and  hand structure


JOINTS OF THE WRIST AND HAND

Wrist Joint—Characteristics and Arthrokinematics

The distal radioulnar (RU) joint is not part of the wrist joint, although pain and impairments in this forearm articulation are often described by the patient as wrist pain.  The wrist joint is multiarticular and is made up of two compound joints. It is biaxial, allowing flexion (volar flexion), extension (dorsiflexion), radial deviation (abduction), and ulnar deviation (adduction). Stability is provided by numerous ligaments: the ulnar and radial collateral, the dorsal and volar (palmar) radiocarpal, the ulnocarpal, and the intercarpal. The pisiform is categorized as a carpal and is aligned volar to the triquetrum in the proximal row of carpals. It is not part of the wrist joint per se but functions as a sesamoid bone in the flexor carpi ulnaris tendon.

Radiocarpal Joint

Characteristics. The radiocarpal (RC) joint is enclosed in a loose but strong capsule that is reinforced by the ligaments. shared with the midcarpal joint. The biconcave articulating surface is the distal end of the radius and radioulnar disk (discus articularis); it is angled slightly volarward and ulnarward. The biconvex articulating surface is the combined proximal surface of the scaphoid, lunate, and triquetrum. The triquetrum primarily articulates with the disk. These three carpals are bound together with numerous interosseous ligaments.

Arthrokinematics. With motions of the wrist, the convex proximal row of carpals slides in the direction opposite the physiological motion of the hand.

Midcarpal Joint

Characteristics. The midcarpal joint is a compound joint between the two rows of carpals. It has a capsule that is also continuous with the intercarpal articulations. The combined distal surfaces of the scaphoid, lunate, and triquetrum articulate with the combined proximal surfaces of the trapezium, trapezoid, capitate, and hamate.

Arthrokinematics. The articulating surfaces of the capitate and hamate are, in essence, convex and slide on the concave articulating surfaces of a portion of the scaphoid, lunate, and triquetrum so with flexion and extension, as well as radial and ulnar deviation, their combined surfaces slide opposite the physiological motion. The articulating surfaces of the trapezium and trapezoid are concave and slide on the convex distal surface of the scaphoid so with flexion and extension their combined surfaces slide in the same direction as the physiological motion. Because the trapezoid is bound to the capitate, they cannot slide in opposite directions during radial and ulnar deviation. The trapezii (the trapezium and trapezoid) therefore slide in a dorsal direction on the scaphoid during radial deviation and in a volar direction during ulnar deviation. Physiological motions of the wrist result in a complex motion between the proximal and distal row of carpals. Because the concave trapezii slide in a dorsal direction on the scaphoid and the convex capitate and hamate slide in a volar direction on the lunate and triquetrum during extension and radial deviation, the resulting motion is a supination twist of the distal row on the proximal row. A pronation twist occurs during flexion and ulnar deviation as the trapezii slide volarly and the capitate and hamate slide dorsally.

 

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