Wrist and hand
The wrist is the proximal segment of the hand formed by a collection of multiple joints and bones. Its complex bone framework consists of the distal end of the radius, articular disc overlying the distal end of the ulna, eight carpal bones (scaphoid, lunate, triquetral, pisiform, trapezium, trapezoid, capitate and hamate), and the proximal portions of the 5 metacarpal bones.
Articulations, joint capsule and ligaments
The wrist (or radiocarpal) joint is a complex condyloid type of synovial joint that bridges the hand to the forearm. Its position can be indicated by the imaginary line joining the styloid processes of the radius and ulna, or by the proximal wrist crease. It consists of the distal end of the radius, articular disc of the distal radioulnar joint, and the proximal row of carpal bones (scaphoid, lunate, triquetrum and pisiform), except for the pisiform.
A fibrous outer layer of the joint capsule encloses the wrist and attaches to the distal ends of the radius and ulna, and the scaphoid, lunate, and triquetrum carpal bones. Its internal layer is comprised of a synovial membrane that secretes synovial fluid to lubricate the joint. The wrist capsule is reinforced by the palmar radiocarpal, palmar ulnocarpal, and dorsal radiocarpal ligaments. In addition, it is reinforced laterally by the radial collateral ligament, and medially by the ulnar collateral ligament. All of these ligaments provide strength and support for the wrist during movement. The wrist allows movement around two axes. The hand can be abducted (radial deviation), adducted (ulnar deviation), flexed, and extended.
The hand is the region of the upper limb that is distal to the forearm and wrist joint. It is formed of the carpus (wrist), metacarpus and the digits (five fingers including the thumb). It has an anterior surface (palm) and a posterior surface (dorsum of hand), both of which are richly supplied with sensory endings for touch, pain, and temperature. The hand is both a sensory and mechanical tool. Its features are made to facilitate the position of the hand in space.
The skeleton of the hand consists of eight carpals, five metacarpals (I- V), and the phalanges (each digit has three, except for the thumb, it has two). The carpal bones tend to function as a unit with the metacarpals of the index, middle, ring, and little fingers, while the thumb metacarpals function independently and have increased flexibility at the carpometacarpal joint, allowing thumb opposition to the fingers.
The intrinsic muscles of the hand are present entirely in the hand. They consist of the palmar brevis, interossei, adductor pollicis, thenar, hypothenar, and lumbrical muscles. These muscles are responsible for the execution of precise movement with the fingers and thumb (‘precision grip’). The intrinsic muscles of the hand are innervated by the deep branch of the ulnar nerve, except for the two lumbrical and three thenar muscles that are innervated by the median nerve. The extrinsic long flexor and extensor muscles of the hand are muscles that originate in the forearm and attach in the hand. They are responsible for forceful gripping with the hand (‘power grip’).