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The hand is a prehensile, multi-fingered appendage located at the end of the forearm.
The human hand normally has five digits: four fingers plus one thumb.
The hand has 27 bones, not including the sesamoid bone, the number of which varies between people,
14 of the bones are the phalanges (proximal, intermediate and distal) of the fingers and thumb.
The metacarpal bones connect the fingers and the carpal bones of the wrist.
Each human hand has five metacarpals and eight carpal bones.
Fingers contain some of the densest areas of nerve endings are found in the fingers, with the richest source of tactile feedback.
The fingers have the greatest positioning capability of the body.
The sense of touch is intimately associated with hands.
The hand is dominantly controlled by the opposing brain hemisphere.
Handedness reflects individual brain functioning.
An adult human male’s hand weighs about a pound.
The volar surface of the hand, the palm, is the central region of the anterior part of the hand.
The palm is located superficially to the metacarpus.
The skin of the palm contains dermal papillae to increase friction.
These dermal papillae as are also present on the fingers and used for fingerprints.
The dorsal surface of the hand, the corresponding area on the posterior part of the hand, to the palm, is known as the opisthenar.
The opisthenar is the back of the hand.
The heel of the hand is the area anteriorly to the bases of the metacarpal bones, located
In the proximal part of the palm is the heel of the hand, anterior to the bases of the metacarpal bones.
The heel of the palm sustains most pressure when using the palm of the hand for support.
The fingers can be folded over the palm which allows the grasping of objects.
Each finger, has a colloquial name to distinguish it from the others:
index finger, pointer finger, forefinger, or 2nd digit
middle finger or long finger or 3rd digit
ring finger or 4th digit
little finger, pinky finger, small finger, baby finger, or 5th digit
The thumb is connected to the first metacarpal bone and trapezium.
Opposable thumbs are identified by the ability to be brought opposite to the fingers, a muscle action known as opposition.
The hand consists of 27 bones.
There are eight short carpal bones of the wrist are organized into a proximal row which articulates with the bones of the forearm, and a distal row, which articulates with the bases of the five metacarpal bones of the hand.
The proximal row of carpal bones are the scaphoid, lunate, triquetral and pisiform.
The distal row of carpal bones are the trapezium, trapezoid, capitate and hamate.
The heads of the metacarpals will each in turn articulate with the bases of the proximal phalanx of the fingers and thumb.
The finger articulations are the metacarpophalangeal joints known as the knuckles
The palmar aspect of the first metacarpophalangeal joints are small, almost spherical bones called the sesamoid bones.
Fourteen phalanges make up the fingers and thumb, and are numbered I-V, thumb to little finger.
The four fingers each consist of three phalanx bones: proximal, middle, and distal, while the thumb only consists of a proximal and distal phalanx.
Because supination and pronation,the ulna and radius are sometimes considered part of the skeleton of the hand.
The sesamoid bones in the hand are small ossified nodes embedded in tendons.
The sesamoid bone exact number varies between people.
A pair of sesamoid bones are found at virtually all thumb metacarpophalangeal joints.
Sesamoid bones are common at the interphalangeal joint of the thumb (72.9%) and at the metacarpophalangeal joints of the little finger (82.5%) and the index finger (48%).
Rarely, .sesamoid bones have been found in all the metacarpophalangeal joints and all distal interphalangeal joints except that of the long finger.
The articulations of the hand are:
interphalangeal articulations of the fingers
metacarpophalangeal joints
intercarpal articulations
The fixed and mobile parts of the hand form bony arches:
Longitudinal arches: the rays formed by the finger bones and their associated metacarpal bones.
Transverse arches-formed by the carpal bones and distal ends of the metacarpal bones.
Oblique arches-between the thumb and four fingers.
Of the longitudinal arches or rays of the hand, that of the thumb is the most mobile, and the least longitudinal.
The phalangeal joints of the index finger, have some independence to its finger, due to the arrangement of its flexor and extension tendons.
The carpal bones form two transversal rows, each forming an arch concave on the palmar side.
The proximal arch simultaneously adapts to the articular surface of the radius and to the distal carpal row, and is by necessity flexible.
The capitate of the distal arch, moves together with the metacarpal bones and the distal arch is therefore rigid.
The stability of these arches is more dependent of the ligaments and capsules of the wrist than of the interlocking carpal bones.
The wrist is therefore more stable in flexion than in extension.
The ligaments that maintain the distal carpal arches are the transverse carpal ligament and the intercarpal ligaments.
The transverse carpal ligament and the intercarpal ligaments form the carpal tunnel and contribute to the deep and superficial palmar arches.
The arch formed by the distal ends of the metacarpal bones is flexible due to the mobility of the peripheral metacarpals, i.e. thumb and little finger.
The middle finger, is the central-most metacarpal bone, and is the most rigid.
The middle finger and its two surrounding digits are tied to the carpus by the metacarpal bones.
The thumb metacarpal is independent and articulates only with the trapezium.
The fifth metacarpal is semi-independent with the fourth metacarpal which forms a transitional element to the fifth metacarpal.
The arch of the index finger functionally is the most important, especially for precision gripping.
The thumb is the principal digit of the hand, giving value to all the other fingers.
The thumb, with the index and middle finger, forms the dynamic tridactyl configuration responsible for most grips not requiring force.
Hand muscles can be subdivided into two groups: the extrinsic and intrinsic muscle groups.
The extrinsic hand muscle groups, with their muscle belly located on the forearm. are the long flexors and extensors.
The intrinsic hand muscle groups are the thumb and little finger muscles; the interosseous muscles originating between the metacarpal bones; and the lumbrical muscles.
The fingers have two long flexor muscles, located on the underside of the forearm, and inserting by tendons to the phalanges of the fingers.
The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx.
The flexors allow for the bending of the fingers.
The thumb has one long flexor and a short flexor in the thenar muscle group.
Additionally the thumb has other muscles in the thenar group,the opponens and abductor brevis muscles, which move the thumb in opposition, making grasping possible.
The extensors, located on the back of the forearm and are connected to the dorsum of the fingers.
The tendons unite with the interosseous and lumbrical muscles to form the extensorhood mechanism, the primary function of which is to straighten out the digits.
The forearm has two extensor tendons to the thumb tendons of these form the anatomical snuff box.
The index finger and the little finger have an extra extensor muscle.
The hand is innervated by the radial, median, and ulnar nerves.
The radial nerve supplies the finger extensors and the thumb abductor, the muscles that extends at the wrist and metacarpophalangeal joints, and that abducts and extends the thumb.
The median nerve supplies the flexors of the wrist and digits, the abductors and opponens of the thumb, the first and second lumbrical.
The ulnar nerve supplies the remaining intrinsic muscles of the hand.
All muscles of the hand are innervated by the brachial plexus (C5–T1).
Radial nerve innervates: Extensors: carpi radialis longus and brevis, digitorum, digiti minimi, carpi ulnaris, pollicis longus and brevis, and indicis.
Other: abductor pollicis longus.
Median nerve innervates: Flexors: carpi radialis, pollicis longus, digitorum profundus (half), superficialis, and pollicis brevis (superficial head).
Other: palmaris longus. abductor pollicis brevis, opponens pollicis, and first and second lumbricals.
Ulnar nerve innervates: Flexor carpi ulnaris, flexor digitorum profundus (half), palmaris brevis, flexor digiti minimi, abductor digiti minimi, opponens digiti minimi, adductor pollicis, flexor pollicis brevis (deep head), palmar and dorsal interossei, and third and fourth lumbricals.
Sensory innervation:
Radial nerve supplies the skin on the back of the hand from the thumb to the ring finger and the dorsal aspects of the index, middle, and half ring fingers as far as the proximal interphalangeal joints.
Median nerve supplies the palmar side of the thumb, index, middle, and half ring fingers. Dorsal branches innervates the distal phalanges of the index, middle, and half ring fingers.
The ulnar nerve supplies the ulnar third of the hand, both at the palm and the back of the hand, and the little and half ring fingers.
Variation to this general pattern exists, except for the little finger and volar surface of the index finger.
The glabrous (hairless) skin on the palm, is relatively thick.
The palm can be bent along the hand’s flexure lines where the skin is tightly bound to the underlying tissue and bones.
The hands’ palms are usually lighter compared to the other side of the hand, and the rest of the body’s skin,
In the dermis of palmoplantar skin genes exist to inhibit melanin production and the ability to tan.
These genes promote the thickening of the stratum lucidum and stratum corneum layers of the epidermis.
All parts of the hand’s skin involved in grasping are covered by papillary ridges, known as fingerprints, acting as friction pads.
The dorsal side of the hand has hairy skin, is thin, soft, and pliable, so that the skin can recoil when the fingers are stretched.
The skin of the dorsal side can be moved across the hand up to 3 cm.
The web of the hand is a fold of skin which connects the digits.18].
The ratio of the length of the index finger to the length of the ring finger in adults is affected by the level of exposure to male sex hormones of the embryo in utero.
This digit ratio is below 1 for both sexes but it is lower in males than in females on average.
Polydactyly is the presence of more than the usual number of fingers.
The fingers may be fused in a disorder known as syndactyly.
The autoimmune disease rheumatoid arthritis can affect the hand, particularly the joints of the fingers.
Some conditions can be treated by hand surgery: carpal tunnel syndrome, and Dupuytren’s contracture.
A common fracture of the hand is a scaphoid fracture.
A scaphoid fracture is the commonest carpal bone fracture and can be slow to heal due to a limited blood flow to the bone.
Fractures to the base of the thumb include Rolando fractures, Bennet’s fracture, and Gamekeeper’s thumb.
Boxer’s fracture, is to the neck of a metacarpal.
Grasping, known as power grip, is supplemented by the precision grip between the thumb and the distal finger pads made possible by the opposable thumbs.
Direct connections between neurons in cortical motor areas and spinal motoneurons, giving the cerebral cortex monosynaptic control over the motoneurons of the hand muscle.