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Hand
Back of a human's left hand
Front of a human's left hand
Details
VeinDorsal venous network of hand
NerveUlnar, median, radial nerves
Identifiers
Latinmanus
MeSHD006225
TA98A01.1.00.025
TA2148
FMA9712
Anatomical terminology

A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "hand" and fingerprints extremely similar to human fingerprints) are often described as having "hands" instead of paws on their front limbs. The raccoon is usually described as having "hands" though opposable thumbs are lacking.[1]

Some evolutionary anatomists use the term hand to refer to the appendage of digits on the forelimb more generally—for example, in the context of whether the three digits of the bird hand involved the same homologous loss of two digits as in the dinosaur hand.[2]

The human hand usually has five digits: four fingers plus one thumb;[3][4] however, these are often referred to collectively as five fingers, whereby the thumb is included as one of the fingers.[3][5][6] It has 27 bones, not including the sesamoid bone, the number of which varies among people,[7] 14 of which 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[8] and eight carpal bones.

Fingers contain some of the densest areas of nerve endings in the body, and are the richest source of tactile feedback. They also have the greatest positioning capability of the body; thus, the sense of touch is intimately associated with hands. Like other paired organs (eyes, feet, legs) each hand is dominantly controlled by the opposing brain hemisphere, so that handedness—the preferred hand choice for single-handed activities such as writing with a pencil—reflects individual brain functioning.

Among humans, the hands play an important function in body language and sign language. Likewise, the ten digits of two hands and the twelve phalanges of four fingers (touchable by the thumb) have given rise to number systems and calculation techniques.

Structure

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Many mammals and other animals have grasping appendages similar in form to a hand such as paws, claws, and talons, but these are not scientifically considered to be grasping hands. The scientific use of the term hand in this sense to distinguish the terminations of the front paws from the hind ones is an example of anthropomorphism. The only true grasping hands appear in the mammalian order of primates. Hands must also have opposable thumbs, as described later in the text.

The hand is located at the distal end of each arm. Apes and monkeys are sometimes described as having four hands, because the toes are long and the hallux is opposable and looks more like a thumb, thus enabling the feet to be used as hands.

The word "hand" is sometimes used by evolutionary anatomists to refer to the appendage of digits on the forelimb such as when researching the homology between the three digits of the bird hand and the dinosaur hand.[2]

An adult human male's hand weighs about a pound.[9]

Areas

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Human hand parts

Areas of the human hand include:

  • The palm (volar), which is the central region of the anterior part of the hand, located superficially to the metacarpus. The skin in this area contains dermal papillae to increase friction, such as are also present on the fingers and used for fingerprints.
  • The opisthenar area (dorsal) is the corresponding area on the posterior part 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. It is the area that sustains most pressure when using the palm of the hand for support, such as in handstand. Its skeletal foundation is formed by the distal row of carpal bones (specifically the hamate, capitate, trapezoid, and trapezium) and the bases of the metacarpal bones. The skin is thick and tough, adapted for pressure and friction, a layer of subcutaneous fat and connective tissue provides cushioning, and palmar fascia contributes to the palm's shape and stability.

There are five digits attached to the hand, notably with a nail fixed to the end in place of the normal claw. The four fingers can be folded over the palm which allows the grasping of objects. Each finger, starting with the one closest to the thumb, has a colloquial name to distinguish it from the others:

The thumb (connected to the first metacarpal bone and trapezium) is located on one of the sides, parallel to the arm. A reliable way of identifying human hands is from the presence of opposable thumbs. Opposable thumbs are identified by the ability to be brought opposite to the fingers, a muscle action known as opposition.

Bones

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Bones of the human hand
An animated gif of a hand's bones splaying
Hand-bone animation (metacarpal movement is exaggerated, other than on the thumb)
Image showing the carpal bones

The skeleton of the human hand consists of 27 bones:[10] the eight short carpal bones of the wrist are organized into a proximal row (scaphoid, lunate, triquetral and pisiform) which articulates with the bones of the forearm, and a distal row (trapezium, trapezoid, capitate and hamate), which articulates with the bases of the five metacarpal bones of the hand. The heads of the metacarpals will each in turn articulate with the bases of the proximal phalanx of the fingers and thumb. These articulations with the fingers are the metacarpophalangeal joints known as the knuckles. At the palmar aspect of the first metacarpophalangeal joints are small, almost spherical bones called the sesamoid bones. The fourteen phalanges make up the fingers and thumb, and are numbered I-V (thumb to little finger) when the hand is viewed from an anatomical position (palm up). The four fingers each consist of three phalanx bones: proximal, middle, and distal. The thumb only consists of a proximal and distal phalanx.[11] Together with the phalanges of the fingers and thumb these metacarpal bones form five rays or poly-articulated chains.

Because supination and pronation (rotation about the axis of the forearm) are added to the two axes of movements of the wrist, the ulna and radius are sometimes considered part of the skeleton of the hand.

There are numerous sesamoid bones in the hand, small ossified nodes embedded in tendons; the exact number varies between people:[7] whereas a pair of sesamoid bones are found at virtually all thumb metacarpophalangeal joints, sesamoid bones are also 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%). In rare cases, sesamoid bones have been found in all the metacarpophalangeal joints and all distal interphalangeal joints except that of the long finger.

The articulations are:

Arches

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Arches of the hand
Red: one of the oblique arches
Brown: one of the longitudinal arches of the digits
Dark green: transverse carpal arch
Light green: transverse metacarpal arch

The fixed and mobile parts of the hand adapt to various everyday tasks by forming 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), and 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). While the ray formed by the little finger and its associated metacarpal bone still offers some mobility, the remaining rays are firmly rigid. The phalangeal joints of the index finger, however, offer some independence to its finger, due to the arrangement of its flexor and extension tendons.[12]

The carpal bones form two transversal rows, each forming an arch concave on the palmar side. Because the proximal arch simultaneously has to adapt to the articular surface of the radius and to the distal carpal row, it is by necessity flexible. In contrast, the capitate, the "keystone" 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 shapes of the carpal bones, and the wrist is therefore more stable in flexion than in extension.[12] The distal carpal arch affects the function of the CMC joints and the hands, but not the function of the wrist or the proximal carpal arch. The ligaments that maintain the distal carpal arches are the transverse carpal ligament and the intercarpal ligaments (also oriented transversally). These ligaments also form the carpal tunnel and contribute to the deep and superficial palmar arches. Several muscle tendons attaching to the TCL and the distal carpals also contribute to maintaining the carpal arch.[13]

Compared to the carpal arches, the arch formed by the distal ends of the metacarpal bones is flexible due to the mobility of the peripheral metacarpals (thumb and little finger). As these two metacarpals approach each other, the palmar gutter deepens. The central-most metacarpal (middle finger) is the most rigid. It and its two neighbors are tied to the carpus by the interlocking shapes of the metacarpal bones. The thumb metacarpal only articulates with the trapezium and is therefore completely independent, while the fifth metacarpal (little finger) is semi-independent with the fourth metacarpal (ring finger) which forms a transitional element to the fifth metacarpal.[12]

Together with the thumb, the four fingers form four oblique arches, of which the arch of the index finger functionally is the most important, especially for precision grip, while the arch of the little finger contribute an important locking mechanism for power grip. The thumb is undoubtedly the "master digit" of the hand, giving value to all the other fingers. Together with the index and middle finger, it forms the dynamic tridactyl configuration responsible for most grips not requiring force. The ring and little fingers are more static, a reserve ready to interact with the palm when great force is needed.[12]

See also: arches of the foot

Muscles

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Main article: Muscles of the hand
Muscles and other structures of wrist and palm

The muscles acting on the hand can be subdivided into two groups: the extrinsic and intrinsic muscle groups. The extrinsic muscle groups are the long flexors and extensors. They are called extrinsic because the muscle belly is located on the forearm.

Intrinsic

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The intrinsic muscle groups are the thenar (thumb) and hypothenar (little finger) muscles; the interosseous muscles (four dorsally and three volarly) originating between the metacarpal bones; and the lumbrical muscles arising from the deep flexor (and are special because they have no bony origin) to insert on the dorsal extensor hood mechanism.[14]

Extrinsic

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Extensor compartments of wrist (back of hand)

The fingers have two long flexors, located on the underside of the forearm. They insert 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 actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group (opponens and abductor brevis muscle), moving the thumb in opposition, making grasping possible.

The extensors are located on the back of the forearm and are connected in a more complex way than the flexors to the dorsum of the fingers. The tendons unite with the interosseous and lumbrical muscles to form the extensorhood mechanism. The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuff box. Also, the index finger and the little finger have an extra extensor used, for instance, for pointing. The extensors are situated within 6 separate compartments.

Compartment 1 (Most radial) Compartment 2 Compartment 3 Compartment 4 Compartment 5 Compartment 6 (Most ulnar)
Abductor pollicis longus Extensor carpi radialis longus Extensor pollicis longus Extensor indicis Extensor digiti minimi Extensor carpi ulnaris
Extensor pollicis brevis Extensor carpi radialis brevis Extensor digitorum communis

The first four compartments are located in the grooves present on the dorsum of inferior side of radius while the 5th compartment is in between radius and ulna. The 6th compartment is in the groove on the dorsum of inferior side of ulna.

Nerve supply

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Cutaneous innervation of the upper limb

The hand is innervated by the radial, median, and ulnar nerves.

Motor

The radial nerve supplies the finger extensors and the thumb abductor, thus the muscles that extends at the wrist and metacarpophalangeal joints (knuckles); 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.[15]

All muscles of the hand are innervated by the brachial plexus (C5–T1) and can be classified by innervation:[16]

Nerve Muscles
Radial Extensors: carpi radialis longus and brevis, digitorum, digiti minimi, carpi ulnaris, pollicis longus and brevis, and indicis.
Other: abductor pollicis longus.
Median 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 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

The 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. The 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.[15]

There is a considerable variation to this general pattern, except for the little finger and volar surface of the index finger. For example, in some individuals, the ulnar nerve supplies the entire ring finger and the ulnar side of the middle finger, whilst, in others, the median nerve supplies the entire ring finger.[15]

Blood supply

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Arteries of the right hand (palmar view)

The hand is supplied with blood from two arteries, the ulnar artery and the radial artery. These arteries form three arches over the dorsal and palmar aspects of the hand, the dorsal carpal arch (across the back of the hand), the deep palmar arch, and the superficial palmar arch. Together these three arches and their anastomoses provide oxygenated blood to the palm, the fingers, and the thumb.

The hand is drained by the dorsal venous network of the hand with deoxygenated blood leaving the hand via the cephalic vein and the basilic vein.

Skin

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Left: Papillary ridges of palm
Right: Sexual dimorphism

The glabrous (hairless) skin on the front of the hand, the palm, is relatively thick and can be bent along the hand's flexure lines where the skin is tightly bound to the underlying tissue and bones. Compared to the rest of the body's skin, the hands' palms (as well as the soles of the feet) are usually lighter—and even much lighter in dark-skinned individuals, compared to the other side of the hand. Indeed, genes specifically expressed in the dermis of palmoplantar skin inhibit melanin production and thus the ability to tan, and promote the thickening of the stratum lucidum and stratum corneum layers of the epidermis. All parts of the skin involved in grasping are covered by papillary ridges (fingerprints) acting as friction pads. In contrast, the hairy skin on the dorsal side is thin, soft, and pliable, so that the skin can recoil when the fingers are stretched. On the dorsal side, the skin can be moved across the hand up to 3 cm (1.2 in); an important input the cutaneous mechanoreceptors.[17]

The web of the hand is a "fold of skin which connects the digits".[18] These webs, located between each set of digits, are known as skin folds (interdigital folds or plica interdigitalis). They are defined as "one of the folds of skin, or rudimentary web, between the fingers and toes".[19]

Variation

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Further information: Digit ratio

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.

Functions

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In primates, hands are not only used for locomotion, but can be used for hand movements like grasping and gripping onto objects. In apes, hands are also good at hand movements not involving grasping, like pushing, lifting, or tapping the keys of a typewriter or piano.[20]

Clinical significance

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X-ray of the left hand of a ten-year-old boy with polydactyly

A number of genetic disorders affect the hand. Polydactyly is the presence of more than the usual number of fingers. One of the disorders that can cause this is Catel-Manzke syndrome. The fingers may be fused in a disorder known as syndactyly. Or there may be an absence of one or more central fingers—a condition known as ectrodactyly. Additionally, some people are born without one or both hands (amelia). Hereditary multiple exostoses of the forearm—also known as hereditary multiple osteochondromas—is another cause of hand and forearm deformity in children and adults.[21]

There are several cutaneous conditions that can affect the hand including the nails.

The autoimmune disease rheumatoid arthritis can affect the hand, particularly the joints of the fingers.

Some conditions can be treated by hand surgery. These include carpal tunnel syndrome, a painful condition of the hand and fingers caused by compression of the median nerve, and Dupuytren's contracture, a condition in which fingers bend towards the palm and cannot be straightened. Similarly, injury to the ulnar nerve may result in a condition in which some of the fingers cannot be flexed.

A common fracture of the hand is a scaphoid fracture—a fracture of the scaphoid bone, one of the carpal bones. This is the commonest carpal bone fracture and can be slow to heal due to a limited blood flow to the bone. There are various types of fracture to the base of the thumb; these are known as Rolando fractures, Bennet's fracture, and Gamekeeper's thumb. Another common fracture, known as Boxer's fracture, is to the neck of a metacarpal. One can also have a broken finger.

Evolution

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Hands of a Javanese tree shrew and a human

The prehensile hands and feet of primates evolved from the mobile hands of semi-arboreal tree shrews that lived about 60 million years ago. This development has been accompanied by important changes in the brain and the relocation of the eyes to the front of the face, together allowing the muscle control and stereoscopic vision necessary for controlled grasping. This grasping, also known as power grip, is supplemented by the precision grip between the thumb and the distal finger pads made possible by the opposable thumbs. Hominidae (great apes including humans) acquired an erect bipedal posture about 3.6 million years ago, which freed the hands from the task of locomotion and paved the way for the precision and range of motion in human hands.[22] Functional analyses of the features unique to the hand of modern humans have shown that they are consistent with the stresses and requirements associated with the effective use of Paleolithic stone tools.[23] It is possible that the refinement of the bipedal posture in the earliest hominids evolved to facilitate the use of the trunk as leverage in accelerating the hand.[24]

While the human hand has unique anatomical features, including a longer thumb and fingers that can be controlled individually to a higher degree, the hands of other primates are anatomically similar and the dexterity of the human hand can not be explained solely on anatomical factors. The neural machinery underlying hand movements is a major contributing factor; primates have evolved direct connections between neurons in cortical motor areas and spinal motoneurons, giving the cerebral cortex monosynaptic control over the motoneurons of the hand muscles; placing the hands "closer" to the brain.[25] The recent evolution of the human hand is thus a direct result of the development of the central nervous system, and the hand, therefore, is a direct tool of our consciousness—the main source of differentiated tactile sensations—and a precise working organ enabling gestures—the expressions of our personalities.[26]

A gorilla, a large extant primate with small thumbs, and the hand skeleton of Ardipithecus ramidus, a large Pliocene primate with relatively human-like thumbs

There are nevertheless several primitive features left in the human hand, including pentadactyly (having five fingers), the hairless skin of the palm and fingers, and the os centrale found in human embryos, prosimians, and apes. Furthermore, the precursors of the intrinsic muscles of the hand are present in the earliest fishes, reflecting that the hand evolved from the pectoral fin and thus is much older than the arm in evolutionary terms.[22]

The proportions of the human hand are plesiomorphic (shared by both ancestors and extant primate species); the elongated thumbs and short hands more closely resemble the hand proportions of Miocene apes than those of extant primates.[27] Humans did not evolve from knuckle-walking apes,[28] and chimpanzees and gorillas independently acquired elongated metacarpals as part of their adaptation to their modes of locomotion.[29] Several primitive hand features most likely present in the chimpanzee–human last common ancestor (CHLCA) and absent in modern humans are still present in the hands of Australopithecus, Paranthropus, and Homo floresiensis. This suggests that the derived changes in modern humans and Neanderthals did not evolve until 2.5 to 1.5 million years ago or after the appearance of the earliest Acheulian stone tools, and that these changes are associated with tool-related tasks beyond those observed in other hominins.[30] The thumbs of Ardipithecus ramidus, an early hominin, are almost as robust as in humans, so this may be a primitive trait, while the palms of other extant higher primates are elongated to the extent that some of the thumb's original function has been lost (most notably in highly arboreal primates such as the spider monkey). In humans, the big toe is thus more derived than the thumb.[29]

There is a hypothesis suggesting the form of the modern human hand is especially conducive to the formation of a compact fist, presumably for fighting purposes. The fist is compact and thus effective as a weapon. It also provides protection for the fingers.[31][32][33] However, this is not widely accepted to be one of the primary selective pressures acting on hand morphology throughout human evolution, with tool use and production being thought to be far more influential.[23]

Additional images

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  • Illustration of hand and wrist bones
    Illustration of hand and wrist bones
  • Bones of the left hand. Volar surface.
    Bones of the left hand. Volar surface.
  • Bones of the left hand. Dorsal surface.
    Bones of the left hand. Dorsal surface.
  • Static adult human physical characteristics of the hand
    Static adult human physical characteristics of the hand
  • X-ray showing joints
    X-ray showing joints
  • Hand bone anatomy

See also

[edit]
This article uses anatomical terminology.

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Hand

View on Grokipedia
from Grokipedia
The hand is the distal portion of the in humans, comprising the , palm, and five digits (thumb and four fingers), and is characterized by its exceptional dexterity, flexibility, and capacity for precise manipulation essential to daily activities such as grasping, gesturing, and tool use. Composed of a complex arrangement of bones, joints, muscles, tendons, ligaments, nerves, and blood vessels, the hand enables both powerful grips for heavy objects and fine for delicate tasks like writing or . Its anatomical sophistication allows for opposition of the against the fingers, a key feature in that is particularly developed in humans to facilitate advanced functionality. The skeletal framework of the hand consists of 27 bones. Together, the two hands contain 54 bones, representing approximately 25% of the total number of bones in the adult . These include eight in the (arranged in proximal and distal rows: scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, and hamate), five forming the palm, and 14 phalanges in the digits (three per finger—proximal, middle, and distal—and two in : proximal and distal). In addition to these primary bones, small sesamoid bones are often present at certain s, such as the metacarpophalangeal (MCP) joint of , to enhance stability and reduce during movement. The joints of the hand—such as the carpometacarpal (CMC), MCP, and interphalangeal (IP) joints—provide the necessary mobility, with 's saddle-shaped CMC allowing for a wide including opposition and circumduction. Muscular support for hand movements arises from over 30 muscles, divided into extrinsic muscles originating in the forearm and intrinsic muscles located within the hand itself. Extrinsic muscles, such as the forearm flexors and extensors, control gross actions like flexion and extension via long tendons that pass through the carpal tunnel and extensor retinaculum. Intrinsic muscles include the thenar group (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis) for thumb movements, the hypothenar group for the little finger, and interossei and lumbrical muscles for fine finger adjustments, enabling abduction, adduction, and coordinated flexion-extension patterns. Ligaments and tendon sheaths stabilize these structures, while the rich neurovascular supply—provided by the radial, median, and ulnar nerves for sensation and motor control, and dual arterial arches (superficial and deep palmar) for blood flow—ensures precise innervation and oxygenation, with the palm alone containing about 17,000 touch receptors for detecting pressure, vibration, and texture. Functionally, the hand's design supports two primary grip types: the power grip for enclosing large objects and the precision grip for manipulating small items, both relying on thumb opposition and synergistic muscle action. This versatility has evolutionary significance, contributing to human tool-making and cultural development, though it also makes the hand vulnerable to injuries like fractures, tendonitis, or due to its intricate structure. Overall, the hand's integration of skeletal, muscular, and neural elements exemplifies biomechanical efficiency, allowing for a remarkable range of motions controlled by the contralateral , with about 90% of individuals exhibiting a dominant hand .

Anatomy

Bones and Joints

The human hand contains 27 bones that form its skeletal framework, enabling precise movement and manipulation. These bones are divided into three main groups: the carpal bones of the wrist, the metacarpal bones of the palm, and the phalanges of the fingers. The eight carpal bones, arranged in two rows, articulate with the forearm's radius and ulna proximally and the metacarpals distally. The proximal row includes the scaphoid, lunate, triquetrum, and pisiform, while the distal row consists of the trapezium, trapezoid, capitate, and hamate. The five metacarpal bones form the palm, each extending from a carpal bone to the base of a digit, with the first metacarpal (thumb) being the shortest and most mobile. The 14 phalanges comprise the digits: the thumb has two (proximal and distal), while each of the other four fingers has three (proximal, middle, and distal). The hand's joints facilitate multiaxial motion essential for dexterity. The carpometacarpal (CMC) joints connect the metacarpals to the carpals; the thumb's CMC joint is a type, allowing opposition through flexion, extension, abduction, adduction, and . The metacarpophalangeal (MCP) joints, between metacarpals and proximal phalanges, are condyloid, permitting flexion, extension, abduction, and adduction. The interphalangeal (IP) joints, linking the phalanges, are joints that primarily enable flexion and extension; the thumb has one IP joint, while other digits have proximal and distal IP joints. The hand maintains structural integrity through four arches supported by ligaments, which distribute weight and enhance stability during grip. The proximal and distal longitudinal arches run along the hand's length, formed by the metacarpals and phalanges, while the transverse carpal arch spans the proximal palm at the carpus and the distal transverse metacarpal arch crosses the metacarpal heads. These arches allow the hand to adapt to objects while preserving a balance between rigidity and flexibility. Certain bones provide specialized functions beyond basic support. Two sesamoid bones at the thumb's MCP joint, embedded in the flexor pollicis brevis tendon, act as pulleys to enhance leverage and reduce tendon friction during pinch and grip. The hook of the hamate, a volar projection of the hamate bone, serves as an attachment site for flexor and opponens digiti minimi tendons, contributing to ulnar-sided stability.

Muscles and Tendons

The of the hand consists of intrinsic and extrinsic muscles that enable precise movements through a complex arrangement of tendons, sheaths, and . Intrinsic muscles originate and insert within the hand, facilitating fine such as finger adduction, abduction, and opposition. Extrinsic muscles, located in the , contribute to gross movements via long tendons that traverse the and insert into the hand's skeletal elements. These structures work in concert to allow the hand's dexterity, with tendons protected by synovial sheaths and stabilized by pulley systems to optimize force transmission and prevent bowstringing during flexion and extension. Intrinsic muscles are divided into four main groups: thenar, hypothenar, central compartment, and adductor pollicis. The houses three muscles responsible for thumb mobility: abductor pollicis brevis, which abducts the thumb; flexor pollicis brevis, which flexes the of the thumb; and opponens pollicis, which opposes the thumb to the fingers. These muscles originate from the flexor retinaculum and , inserting into the proximal phalanx or metacarpal of the thumb. The contains three analogous muscles for the : abductor digiti minimi, which abducts the ; flexor digiti minimi brevis, which flexes its ; and opponens digiti minimi, which flexes and opposes the . These originate from the , hook of the hamate, and flexor retinaculum, inserting into the proximal phalanx or fifth metacarpal. The central compartment includes the lumbricals and interossei, which fine-tune finger positioning. Four lumbrical muscles arise from the tendons of flexor digitorum profundus, inserting into the extensor expansions of the fingers to flex the metacarpophalangeal joints and extend the interphalangeal joints. The interossei consist of three palmar interossei, which adduct the index, ring, and little fingers toward the middle finger, and four dorsal interossei, which abduct the fingers away from the middle axis; these originate from the metacarpal shafts and insert into the proximal phalanges and extensor hoods. Adductor pollicis, a triangular muscle in the deep palm, adducts the thumb and originates from the metacarpals and capitate bone, inserting into the thumb's proximal phalanx. Together, these intrinsic muscles enable the hand's opposition and grip precision. Extrinsic muscles originate in the and extend long tendons across the to act on the hand's digits. Flexor tendons include those from flexor digitorum superficialis, which flex the proximal interphalangeal joints of the to little fingers, and flexor digitorum profundus, which flexes the distal interphalangeal joints of the same fingers; flexor pollicis longus flexes the thumb's interphalangeal joint. These tendons pass through the , bifurcating to allow independent digit flexion. Extensor tendons arise from extensor digitorum, which extends the metacarpophalangeal joints of the fingers; extensor pollicis longus and brevis, which extend the thumb's interphalangeal and metacarpophalangeal joints, respectively; and extensor indicis, which extends the independently. These tendons course through dorsal compartments at the , enabling coordinated extension. Tendons in the hand are enveloped by synovial sheaths for and glide smoothly due to a pulley system that anchors them to the bones. Flexor tendons are surrounded by synovial sheaths that begin at the metacarpal necks and extend to the distal phalanges, producing fluid to reduce during movement; the sheaths for the index to ring fingers are independent, while the little finger's often shares a common extension from the . The pulley system comprises five annular pulleys (A1-A5), which are thick, fibrous bands preventing tendon bowstringing, and three cruciate pulleys (C1-C3), which are thinner and allow sheath folding during flexion; A2 and A4 are critical for maintaining mechanical efficiency in the proximal and middle phalanges. Extensor tendons have similar but less extensive sheaths and pulleys on the dorsal side. Innervation of hand muscles primarily involves the and s. The supplies the thenar muscles (abductor pollicis brevis, flexor pollicis brevis superficial head, opponens pollicis) and the first two lumbricals via its recurrent motor branch. The innervates the hypothenar muscles, adductor pollicis, the third and fourth lumbricals, all interossei, and the deep head of flexor pollicis brevis, entering the hand through Guyon's . Extrinsic flexors receive innervation (except flexor digitorum profundus medial half by ulnar), while extensors are supplied by the . This division ensures balanced control for fine and gross hand functions.

Nerves and Blood Supply

The hand receives its nerve supply primarily from three major nerves originating from the brachial plexus: the median nerve (C5-T1 roots), ulnar nerve (C8-T1 roots), and radial nerve (C5-T1 roots). These nerves provide both sensory and motor innervation essential for hand function. The median nerve enters the hand through the carpal tunnel, where it is anatomically vulnerable to compression, and supplies motor innervation to the thenar muscles (abductor pollicis brevis, opponens pollicis, and superficial head of flexor pollicis brevis) and the first two lumbricals, while providing sensory innervation to the palmar surfaces of the thumb, index, middle, and radial half of the ring finger. The ulnar nerve passes through Guyon's canal at the wrist (with potential for anatomical compression there) and the cubital tunnel at the elbow, innervating motor functions in the hypothenar muscles (abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi), interossei (dorsal and palmar), adductor pollicis, and the third and fourth lumbricals (including the deep head of flexor pollicis brevis), with sensory coverage of the ulnar palm, hypothenar eminence, and the ulnar half of the ring and little fingers. The radial nerve contributes minimally to motor supply in the hand, primarily via its posterior interosseous branch to forearm extensors with limited extension to hand extensors, but its superficial branch provides sensory innervation to the dorsal aspects of the thumb, index, middle, and radial half of the ring finger. Sensory innervation of the hand follows dermatomal patterns primarily from C6, C7, and C8 spinal roots, with C6 covering the thumb and index finger, C7 the middle finger, and C8 the ring and little fingers, overlapping via the peripheral nerves described above. The arterial blood supply to the hand arises mainly from the radial and ulnar arteries, which form anastomotic arches to ensure robust circulation. The radial artery enters the hand dorsally and gives off the princeps pollicis artery (supplying the thumb) and radialis indicis artery (supplying the radial side of the index finger), contributing to the deep palmar arch via its deep branch, which anastomoses with the ulnar artery's deep palmar branch to perfuse deep palmar structures and metacarpal arteries. The ulnar artery forms the superficial palmar arch (completed by the superficial palmar branch of the radial artery), supplying superficial palmar skin, digital arteries, and flexor tendons. Venous drainage occurs via a superficial dorsal venous network (forming cephalic and basilic veins) and palmar digital veins, which anastomose and drain proximally. Lymphatic drainage from the hand's superficial structures flows to cubital (epitrochlear) nodes in the cubital fossa, while deep structures drain directly to axillary lymph nodes in the axilla, with vessels accompanying veins and arteries along the upper limb.

Skin and Soft Tissues

The skin of the hand exhibits distinct regional variations adapted to its functional demands. On the palmar surface, the skin is thick and glabrous, lacking hair follicles and characterized by prominent friction ridges, also known as dermatoglyphics, which enhance grip by increasing surface friction during object manipulation. In contrast, the dorsal skin is thinner and more pliable, containing hair follicles and sebaceous glands, which facilitate flexibility over the underlying extensor tendons and bones. Flexion creases, including the distal and proximal palmar creases as well as digital creases at the interphalangeal joints, form permanent folds that allow skin mobility during hand movements without tearing. Subcutaneous fat pads, such as those in the thenar and hypothenar eminences and over the metacarpophalangeal joints, provide cushioning and contribute to the hand's contour, protecting deeper structures from compressive forces. The soft tissues of the hand include specialized ligaments and l structures that support stability and movement. Collateral ligaments at the metacarpophalangeal and interphalangeal joints provide medial and lateral stability, preventing excessive deviation during flexion and extension. Additional ligaments, including the palmar, radial, and ulnar components, reinforce the transverse and longitudinal arches of the hand, maintaining its structural integrity under load. The , a thickened central extension of the , anchors the skin to deeper tissues, protects neurovascular bundles, and helps distribute forces across the palm to prevent excessive bowstringing. Bursae, such as the ulnar and radial bursae surrounding the flexor s, are synovial-lined sacs that secrete lubricating fluid to reduce friction between s and surrounding tissues during repetitive motions. Congenital variations in the skin and soft tissues of the hand can significantly alter its form and function. involves the presence of extra digits, which may be fully formed or rudimentary and often arise from duplication of digital rays during embryonic development. , conversely, features fusion of adjacent digits, ranging from simple skin webbing to complex bony unions, affecting up to 1 in 2,000 to 3,000 births. Hypoplastic represents a spectrum of underdevelopment or absence of the , impacting opposition and pinch strength. Dermatoglyphic patterns on the palms, including whorls, loops, and arches, exhibit racial differences. The of the hand is richly endowed with sensory receptors that enable fine tactile discrimination. Meissner corpuscles, located in the dermal papillae of glabrous , detect low-frequency vibrations and light touch, adapting rapidly to changes in stimulus. Merkel cells, associated with slowly adapting type I afferents, respond to sustained and contribute to spatial acuity, such as in texture . Pacinian corpuscles, deeper in the and , sense high-frequency vibrations and transient , aiding in the detection of tools or surfaces in motion. Ruffini endings monitor stretch and sustained deformation, providing information on position and tension during .

Functions

Movement and Dexterity

The hand exhibits a wide array of primary movements that enable precise manipulation and gross actions. Flexion and extension occur primarily at the metacarpophalangeal (MCP) and interphalangeal (IP) joints, allowing the fingers to curl toward the palm or straighten outward, respectively. Abduction and adduction of the fingers involve spreading or approximating them relative to the hand's midline at the MCP joints, while the thumb's abduction and adduction occur at its carpometacarpal (CMC) joint. Opposition, a hallmark of hand dexterity, involves rotation at the thumb's CMC joint to bring the thumb pad into contact with the fingertips, facilitating pad-to-pad or tip-to-tip interactions. Circumduction combines these motions into a conical path, particularly evident in thumb opposition, which traces an arc from the palm to the base of the . These movements underpin various grip types essential for daily tasks. The power grip, such as the cylindrical grasp used for holding tools like a , envelops an object against the palm using the fingers and adducted thumb for strong force application. In contrast, the precision grip, exemplified by pad-to-pad pinching of small objects like a pen, relies on the thumb and fingertips for accurate control without full palm involvement. The hook grip, involving flexion of the flexor digitorum profundus to carry loads like a handle, maintains the MCP joints in extension while generating force through the IP joints. Biomechanically, force generation in the hand arises from the interplay of intrinsic and extrinsic muscles, with the former providing fine control and the latter delivering power. Intrinsic muscles, including the interossei and lumbricals, produce targeted forces at the MCP joints for dexterity. Extrinsic muscles, such as the flexor digitorum superficialis and profundus originating in the , generate higher forces for gross movements, enabling power grips capable of substantial force in healthy adults. The thumb's opposition arc supports a of about 60-70 degrees in combined flexion-extension and abduction-adduction at the CMC , optimizing leverage for manipulation. Coordination of these elements is crucial for tasks requiring simultaneous joint actions, such as writing or pinching. The lumbrical muscles play a key role by stabilizing the MCP joints in slight flexion during IP joint flexion, preventing paradoxical extension and ensuring smooth force transmission through the extensor mechanism. This action, which involves minimal direct force contribution (2-3% to MCP flexion), enhances precision by maintaining finger alignment and proprioceptive feedback during fine motor activities.

Sensory Perception

The hand's sensory perception is crucial for interacting with the environment, enabling precise tactile and proprioceptive that support manipulation and coordination. Tactile allows differentiation of spatial details through touch, with the two-point threshold—the minimum distance at which two points of contact are perceived as separate—measuring spatial acuity. On the , this threshold is approximately 2-4 , reflecting high receptor density for fine resolution, while on the palm it ranges from 8-12 due to sparser innervation. Stereognosis, the ability to recognize objects by touch alone, integrates these spatial cues with shape and texture information; for instance, individuals can identify common items like keys or coins placed in the hand with eyes closed, relying on somatosensory processing in the . This perceptual capability arises from specialized mechanoreceptors in the . Rapidly adapting receptors include Meissner corpuscles, which detect low-frequency flutter and skin slippage during object handling (5-50 Hz), and Pacinian corpuscles, which respond to high-frequency vibrations (200-300 Hz) for sensing texture and pressure changes. Slowly adapting receptors, such as Merkel disks, provide sustained responses to static indentation and fine texture details, while Ruffini endings detect skin stretch and sustained pressure, contributing to stability. These receptors are densely packed in glabrous (e.g., and palms), with innervation densities of 200-300 mechanoreceptive units per cm² on , compared to much lower densities (around 50-100 per cm²) in hairy on the dorsal hand. Proprioception in the hand informs position and movement sense, primarily through muscle spindles in intrinsic and extrinsic muscles, which detect length changes and velocity to maintain finger positioning without visual input. Joint receptors around metacarpophalangeal and interphalangeal joints supplement this by signaling joint angles and limits, though their role is more prominent in dynamic movements. Together, these mechanisms facilitate hand-eye coordination, allowing seamless integration of tactile and visual feedback for tasks like reaching or threading a needle. Hand laterality may influence sensory acuity, underscoring the hand's adaptability in skilled activities.

Clinical Significance

Injuries and Trauma

Injuries and trauma to the hand are among the most common musculoskeletal issues encountered in emergency settings, often resulting from falls, direct blows, or compressive forces that exploit the region's intricate anatomy and limited protective covering. These acute events can involve bony structures, soft tissues, or neurovascular elements, leading to pain, swelling, and functional impairment if not promptly addressed. The hand's vulnerability stems from its role in daily activities, making timely diagnosis and management essential to restore dexterity and prevent long-term complications such as stiffness or necrosis. Common fractures in hand trauma include scaphoid fractures, boxer's fractures, and phalangeal tuft fractures. Scaphoid fractures typically occur via a fall on an outstretched hand (FOOSH) mechanism, where axial loading in hyperextension and radial deviation shears the bone at its waist (65% of cases), proximal third (25%), or distal third (10%). This injury carries a significant risk of due to the scaphoid's retrograde blood supply, with proximal pole fractures showing up to 100% incidence and distal segments around 33%. Boxer's fractures involve the neck of the fifth metacarpal and represent the most frequent metacarpal injury, arising from a clenched-fist punch that transmits force to the bone's distal aspect. Phalangeal tuft fractures, affecting the distal tip, commonly result from crush mechanisms such as slamming a finger in a , and are often stable due to soft-tissue constraints from the nail plate and pulp. Soft tissue trauma encompasses lacerations, sprains, and crush injuries, each demanding specific attention to preserve gliding and vascular integrity. Lacerations frequently involve flexor s, classified into five zones (I-V) per the Verdan system: Zone I (distal to FDS insertion, e.g., jersey finger avulsion), Zone II (critical "no-man's-land" from A1 pulley to FDS insertion, prone to scarring), Zones III-V (palm to , with increasing sheath protection). Repair techniques emphasize core sutures (e.g., modified Kessler for 4-6 strands) combined with epitendinous reinforcement to minimize gap formation. Sprains like gamekeeper's thumb involve (UCL) tears at the , caused by radial deviation force (e.g., from falls or gripping), leading to instability and potential if the adductor interposes. Crush injuries, often from machinery or heavy objects, cause extensive tissue damage, , and reperfusion issues, with a high risk of in the hand's 10 fascial compartments due to elevated intracompartmental pressures exceeding . Diagnosis begins with a thorough neurovascular assessment, including , sensation, motor function, and the Allen test to evaluate radial and ulnar arterial patency by assessing palmar blush after sequential compression and release. Plain X-rays (standard views: posteroanterior, lateral, oblique) confirm bony fractures in 75-80% of cases initially, though scaphoid injuries may require specialized projections or follow-up imaging. provides dynamic evaluation of ligaments and tendons, while MRI offers detailed soft-tissue visualization to detect occult damage or Stener lesions when X-rays are inconclusive. Initial management prioritizes stabilization and symptom control using the RICE protocol—rest to avoid further damage, ice for and analgesia, compression to limit swelling, and above heart level—applied immediately post-injury. Immobilization via splints or casts (e.g., thumb spica for scaphoid or UCL injuries, ulnar gutter for ) maintains alignment for 3-6 weeks, depending on stability. For unstable fractures or complete / disruptions, surgical fixation is indicated: percutaneous K-wires or screws for scaphoid non-displacements, open reduction with plates for metacarpal necks, or primary repair within 7-10 days. Early referral to a hand specialist ensures optimal outcomes, with protected motion protocols post-immobilization to prevent adhesions.

Disorders and Conditions

Hand disorders encompass a range of chronic and non-traumatic pathologies that impair function, often requiring multifaceted management to alleviate symptoms and restore dexterity. Inflammatory conditions, such as and , are prevalent causes of hand pain and stiffness. primarily affects the carpometacarpal (CMC) joint of the thumb and proximal interphalangeal joints, leading to degeneration and bony enlargements known as , which manifest as firm swellings on the sides of the fingers. Symptoms include joint pain, stiffness, and reduced , exacerbated by repetitive use or cold exposure. , an autoimmune disorder, causes synovial inflammation () in the hand joints, resulting in swelling, warmth, and progressive deformities like ulnar deviation of the fingers due to laxity and . These inflammatory processes can lead to joint erosion and functional limitations if untreated. Nerve entrapment syndromes further contribute to hand dysfunction by compressing peripheral nerves, leading to sensory and motor deficits. arises from compression within the , often due to repetitive motions or idiopathic thickening of the transverse carpal , causing numbness, tingling in the thumb, index, and middle fingers, and nocturnal pain. Diagnostic tests include , elicited by tapping over the to reproduce symptoms, and Phalen's test, where flexion for 60 seconds provokes . In advanced cases, thenar may occur. syndrome involves ulnar nerve entrapment at the elbow, resulting from prolonged flexion or direct pressure, and presents with medial forearm pain, little and ring finger numbness, and intrinsic leading to claw hand deformity, characterized by hyperextension of the metacarpophalangeal joints and flexion of the interphalangeal joints. Other notable disorders include Dupuytren's contracture, trigger finger, and ganglion cysts, each affecting the soft tissues of the hand. Dupuytren's contracture involves progressive thickening and contracture of the palmar fascia, forming nodules and cords that pull the fingers—typically the ring and little—into flexion, limiting extension and grip. This fibroproliferative condition is more common in males of Northern European descent and may be linked to genetic factors. Trigger finger, or stenosing tenosynovitis, results from inflammation and narrowing (stenosis) of the A1 pulley, causing the flexor tendon to catch during motion, producing pain, clicking, and locking of the affected digit, often the thumb or ring finger. Ganglion cysts appear as benign, fluid-filled sacs from synovial herniation at the wrist, usually dorsal, arising from joint or tendon sheath degeneration; they may cause cosmetic concerns, tenderness, or weakness if pressing on nearby structures. Therapeutic approaches for these disorders prioritize conservative measures before escalating to , tailored to symptom severity and patient needs. Conservative treatments include splinting to immobilize affected joints and reduce , nonsteroidal drugs (NSAIDs) for relief, and injections to decrease swelling in conditions like or trigger finger. For persistent cases, surgical interventions such as release to decompress the , decompression, or fasciectomy for are employed, alongside for advanced and tendon transfers to restore motor function in nerve palsies; for Dupuytren's, non-surgical options include injections and percutaneous needle aponeurotomy. Rehabilitation through is integral post-treatment, focusing on exercises to improve strength, , and daily function, often yielding significant gains in hand use for patients with or post-surgical recovery.

Evolution and Development

Comparative Anatomy

The hand in exhibits significant variation adapted to locomotor and manipulative demands. In great apes such as chimpanzees and orangutans, is opposable but shorter relative to the other digits compared to humans, with limited independence due to a less mobile and reliance on long, curved fingers for suspensory locomotion in arboreal environments. This configuration supports powerful hook grips for branch suspension but constrains fine manipulation. In contrast, many monkeys, particularly arboreal species like spider monkeys, feature elongated phalanges that enhance grasping of branches, facilitating hook and span grips during locomotion, though their thumbs are moderately opposable and less specialized for precision than in humans. For example, capuchin monkeys (Cebus) show thumb proportions overlapping with humans, linked to enhanced dexterity for . Non-primate tetrapods display further divergence from the pentadactyl mammalian hand, reflecting adaptations to specialized locomotion. In birds, the skeleton derives from the but features reduced and fused digits: typically three digits remain, with the (digit I) free and the others (II and III) fused into a carpometacarpus for aerodynamic support during flight, eliminating manipulative function. Horses exemplify digit reduction for terrestrial speed, where the central digit (III) is greatly elongated to form the , bearing the animal's weight, while lateral digits (II and IV) are vestigial or absent in modern equids, a pattern evolved from multi-toed ancestors. In cetaceans like whales, the flipper retains a paddle-like form with hyperphalangy—increased phalangeal count per digit (often exceeding 10-14 per digit)—to elongate and streamline the appendage for hydrodynamic propulsion, encasing the in without external digit separation. Key human hand adaptations emphasize dexterity for tool use, including a shortened palm relative to finger length and an elongated thumb that constitutes approximately 35-40% of hand length, enabling robust opposition and pad-to-pad contact. These features facilitated the evolution of the precision grip around 2.6-2.3 million years ago, associated with and the emergence of stone tools, allowing controlled manipulation of objects like flakes and cores. Unlike the elongated digits of arboreal , human fingers are straighter and shorter, optimizing for both precision and power grips in terrestrial settings. Recent research as of 2025 has identified a positive between relative thumb length and brain size across , suggesting that manual dexterity and cognitive abilities co-evolved. Fossil evidence from , exemplified by the "" specimen (AL 288-1, dated ~3.2 million years ago), reveals hand bones with mixed arboreal and terrestrial traits: curved proximal phalanges suggest retention of climbing capabilities, similar to those in chimpanzees for branch suspension, while the robust metacarpals and morphology indicate adaptations for terrestrial and rudimentary manipulation. This mosaic reflects a transitional phase from arboreal ancestry to bipedal terrestriality, with phalangeal curvature (phalanx/metacarpal index ~1.2) supporting occasional tree use alongside ground-based .

Embryonic Development

The embryonic development of the human hand begins during the fourth week of gestation with the formation of the upper limb bud, a paddle-shaped outgrowth arising from the lateral plate mesoderm in the lower cervical region. This bud consists of mesenchyme covered by ectoderm, and its initial growth is directed along three axes: proximodistal, anteroposterior, and dorsoventral. The apical ectodermal ridge (AER), a thickened ectodermal structure at the distal tip of the limb bud, plays a crucial role in proximodistal outgrowth by secreting fibroblast growth factors (FGFs), particularly FGF8 and FGF10, which maintain proliferation of underlying mesenchymal cells. Meanwhile, the zone of polarizing activity (ZPA), located at the posterior margin of the limb bud, establishes anteroposterior polarity through the secretion of Sonic hedgehog (Shh), a signaling molecule that patterns the radial-ulnar axis and determines digit identity. Disruptions in these early signaling pathways can lead to severe congenital anomalies, such as amelia, the complete absence of the limb due to failure of bud initiation. By weeks 6 to 7 of , mesenchymal cells within the limb bud undergo chondrification, forming cartilaginous models (precursors) of the future metacarpals and phalanges through condensation and differentiation into chondrocytes. This process is regulated by signaling molecules like Indian hedgehog (Ihh) and parathyroid hormone-related protein (PTHrP), which coordinate maturation. Primary ossification centers then emerge around week 8 in the diaphyses of the metacarpals and phalanges, where hypertrophic chondrocytes are replaced by via , beginning the transformation from to . Secondary ossification centers appear later in the epiphyses, typically during the fetal period and continuing postnatally, allowing for longitudinal growth. Digit formation occurs between weeks 6 and 8, as the hand plate within the limb develops five radial condensations that outline the future digits, initially connected by interdigital webbing. Regression of the AER signals the cessation of outgrowth, triggering () in the interdigital to sculpt distinct digits; this process proceeds from distal to proximal and is mediated by bone morphogenetic proteins (BMPs), particularly , , and , which induce activation and DNA fragmentation in mesenchymal cells. Concurrently, undergoes approximately 90 degrees of external by week 8 to align with the other digits in the same plane, a movement driven by differential growth and muscle development in the . Disruptions in , such as reduced BMP signaling, can result in (webbed digits), while external factors like amniotic bands—fibrous strands from early amnion rupture—may cause random constrictions, amputations, or deformities in amniotic band . Adequate amniotic fluid volume supports limb positioning and prevents such adhesions, influencing overall growth.

References

  1. https://www.ncbi.nlm.nih.gov/books/NBK279362/
  2. https://www.ncbi.nlm.nih.gov/books/NBK547684/
  3. https://www.ncbi.nlm.nih.gov/books/NBK535382/
  4. https://ouhsc.edu/bserdac/dthompso/web/namics/firstcmc.htm
  5. https://www.ncbi.nlm.nih.gov/books/NBK538343/
  6. https://ouhsc.edu/bserdac/dthompso/web/namics/hand.htm
  7. https://pressbooks-dev.oer.hawaii.edu/anatomyandphysiology/chapter/bones-of-the-upper-limb/
  8. https://www.ncbi.nlm.nih.gov/books/NBK578171/
  9. https://pmc.ncbi.nlm.nih.gov/articles/PMC5892414/
  10. https://humananatomy.host.dartmouth.edu/BHA/public_html/part_2/chapter_11.html
  11. http://people.musc.edu/~bacrotr/knee/handmuscles.htm
  12. https://anatomy.elpaso.ttuhsc.edu/musculoskeletal_system/hand_ans.html
  13. https://ouhsc.edu/bserdac/dthompso/web/namics/labs/wrist1c.htm
  14. http://people.musc.edu/~bacrotr/knee/handmisc.htm
  15. https://digitalcommons.wustl.edu/cgi/viewcontent.cgi?article=1954&context=open_access_pubs
  16. https://www.ncbi.nlm.nih.gov/books/NBK470464/
  17. https://www.ojp.gov/pdffiles1/nij/225323.pdf
  18. https://emedicine.medscape.com/article/1285060-overview
  19. https://pubmed.ncbi.nlm.nih.gov/16607465/
  20. https://www.ncbi.nlm.nih.gov/books/NBK534779/
  21. https://www.physio-pedia.com/Wrist_and_Hand
  22. https://musculoskeletalkey.com/anatomy-2/
  23. https://www.ncbi.nlm.nih.gov/books/NBK541025/
  24. https://orthoinfo.aaos.org/en/diseases--conditions/congenital-hand-differences/
  25. https://pmc.ncbi.nlm.nih.gov/articles/PMC7355096/
  26. https://www.ncbi.nlm.nih.gov/books/NBK541068/
  27. https://pmc.ncbi.nlm.nih.gov/articles/PMC3653006/
  28. https://pmc.ncbi.nlm.nih.gov/articles/PMC1312228/
  29. https://openpub.libraries.rutgers.edu/developmentacrossthelifespan/chapter/upper-extremity-ballistic-skills/
  30. https://pmc.ncbi.nlm.nih.gov/articles/PMC2855501/
  31. https://www.ri.cmu.edu/pub_files/pub4/chang_lillian_y_2008_2/chang_lillian_y_2008_2.pdf
  32. https://pmc.ncbi.nlm.nih.gov/articles/PMC4155599/
  33. https://www.physio-pedia.com/Weber_Two-Point_Discrimination_Test
  34. https://pmc.ncbi.nlm.nih.gov/articles/PMC11436338/
  35. https://www.ncbi.nlm.nih.gov/books/NBK556003/
  36. https://pmc.ncbi.nlm.nih.gov/articles/PMC1281571/
  37. https://www.ncbi.nlm.nih.gov/books/NBK10895/
  38. https://www.ncbi.nlm.nih.gov/books/NBK10812/
  39. https://www.sciencedirect.com/science/article/pii/S0363502305800127
  40. https://pmc.ncbi.nlm.nih.gov/articles/PMC4799424/
  41. https://www.ncbi.nlm.nih.gov/books/NBK557625/
  42. https://www.ncbi.nlm.nih.gov/books/NBK536907/
  43. https://www.orthobullets.com/hand/6034/scaphoid-fracture
  44. https://my.clevelandclinic.org/health/diseases/boxers-fracture
  45. https://radiopaedia.org/cases/phalangeal-tuft-fracture-8?lang=us
  46. https://www.orthobullets.com/hand/6031/flexor-tendon-injuries
  47. https://orthoinfo.aaos.org/en/diseases--conditions/flexor-tendon-injuries/
  48. https://www.ncbi.nlm.nih.gov/books/NBK482383/
  49. https://pubmed.ncbi.nlm.nih.gov/12360060/
  50. https://pmc.ncbi.nlm.nih.gov/articles/PMC7195209/
  51. https://www.ncbi.nlm.nih.gov/books/NBK580565/
  52. https://pmc.ncbi.nlm.nih.gov/articles/PMC9839919/
  53. https://pmc.ncbi.nlm.nih.gov/articles/PMC2597216/
  54. https://www.ncbi.nlm.nih.gov/books/NBK482326/
  55. https://www.ncbi.nlm.nih.gov/books/NBK560890/
  56. https://pmc.ncbi.nlm.nih.gov/articles/PMC4157737/
  57. https://www.ncbi.nlm.nih.gov/books/NBK441999/
  58. https://www.ncbi.nlm.nih.gov/books/NBK448179/
  59. https://pmc.ncbi.nlm.nih.gov/articles/PMC6188276/
  60. https://www.ncbi.nlm.nih.gov/books/NBK538259/
  61. https://pmc.ncbi.nlm.nih.gov/articles/PMC6104141/
  62. https://orthoinfo.aaos.org/en/diseases--conditions/dupuytrens-disease/
  63. https://pmc.ncbi.nlm.nih.gov/articles/PMC2684207/
  64. https://pmc.ncbi.nlm.nih.gov/articles/PMC4956841/
  65. https://www.ncbi.nlm.nih.gov/books/NBK470168/
  66. https://pmc.ncbi.nlm.nih.gov/articles/PMC2871765/
  67. https://pmc.ncbi.nlm.nih.gov/articles/PMC6483762/
  68. https://www.ncbi.nlm.nih.gov/books/NBK526074/
  69. https://www.ncbi.nlm.nih.gov/books/NBK614171/
  70. https://www.mayoclinic.org/diseases-conditions/dupuytrens-contracture/diagnosis-treatment/drc-20371949
  71. https://pmc.ncbi.nlm.nih.gov/articles/PMC10897503/
  72. https://pubmed.ncbi.nlm.nih.gov/17090982/
  73. https://www.nature.com/articles/ncomms8717
  74. https://pmc.ncbi.nlm.nih.gov/articles/PMC1571064/
  75. https://www.poultryhub.org/anatomy-and-physiology/body-systems/skeletal-system
  76. https://royalsocietypublishing.org/doi/10.1098/rsos.171782
  77. https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.20532
  78. https://nymag.com/news/intelligencer/smartphone-thumbs-2012-9/
  79. https://www.healthline.com/health/average-hand-size
  80. https://www.nhm.ac.uk/discover/homo-habilis-early-maker-stone-tools.html
  81. https://royalsocietypublishing.org/doi/10.1098/rstb.2015.0105
  82. https://www.nature.com/articles/s42003-025-08686-5
  83. https://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-afarensis
  84. https://www.ncbi.nlm.nih.gov/books/NBK538240/
  85. https://pmc.ncbi.nlm.nih.gov/articles/PMC4580101/
  86. https://www.ncbi.nlm.nih.gov/books/NBK10048/
  87. https://www.ncbi.nlm.nih.gov/books/NBK545283/
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