hands

Hands are the prehensile structures at the end of the upper limbs that enable manipulation of objects, tactile exploration, and social communication. Each hand consists of the wrist, palm, and digits and contains 27 bones: eight carpal bones in the wrist, five metacarpal bones in the palm, and 14 phalanges in the fingers. The bones form several joints including the radiocarpal and midcarpal joints of the wrist, the metacarpophalangeal joints at the bases of the fingers, and the proximal, middle, and distal interphalangeal joints along the digits.

Soft tissues include flexor tendons on the palm side (notably flexor digitorum superficialis and profundus), extensor tendons on the back of the hand, and the intrinsic muscles of the hand in the palm. The intrinsic muscles are organized into the thenar eminence (thumb), hypothenar eminence (little finger), and the interossei and lumbricals that refine finger movements. Tendons allow flexion and extension, while muscles such as the interossei enable abduction and adduction of the fingers; the opponens pollicis enables thumb opposition.

Neurological control comes from the median, ulnar, and radial nerves, with sensory innervation of the palmar surfaces and fingertips and motor control of most intrinsic and extrinsic hand muscles. Blood supply comes from the radial and ulnar arteries, which form complex palmar arches.

Functionally, hands perform power grips and precision grips, pinch, manipulation, and fine motor tasks. The opposable thumb greatly expands grip versatility and dexterity, enabling delicate tasks such as writing or sewing.

Developmentally, hand structure arises during embryogenesis, with finger pads forming dermal ridges that create fingerprints. Variants include differences in size, dermal patterns, and congenital conditions such as polydactyly or brachydactyly. Clinically relevant conditions include carpal tunnel syndrome, tendon injuries, and arthritis, which can affect strength, sensation, and dexterity.