Hand

Palm and dorsal faces of the human right hand

The hand is generally a prehensile appendage with several fingers located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. To some other vertebrates, the forelimbs are often described as having hands, rather than legs.

In humans, the hand (from Latin manus) is a paired organ that forms part of each of the two extremities of the human body, and is the fourth segment of the upper or thoracic limb. It is located at the end of each of the forearms; It is prehensile and has five fingers. Covers from the wrist to the fingertips.

The human hand for manipulation

Hands are the main organ for physical manipulation of the environment. The tips of the fingers contain one of the areas with the most nerve endings in the human body; they are the main source of tactile information about the environment, so the sense of touch is immediately associated with the hands. As in the other paired organs (eyes, ears, legs), each of the hands is controlled by the cerebral hemisphere on the opposite side of the body. There is always one dominant over the other, which will take care of activities such as handwriting; in this way, the person may be left-handed, if the predominance is left (sinister) or right-handed, if it is right (right); this is a personal trait.

Anatomy of the Human Hand

Axisas de una mano

The human hand is attached to the forearm by a joint called the wrist (bones of which form the carpals) and consists of a central palm (bones of which form the metacarpals) from which five fingers arise. Additionally, the hand is made up of several different muscles and ligaments that allow for a great deal of movement and dexterity.

Fingers

Name the five fingers from the outside in, palm up:

• Thumbalso known as "great finger of the hand" or "first finger of the hand".
• Indexalso known as "second finger of the hand".
• Dedo cordial, also known as "third finger of the hand", "middle finger", "old finger", "heart" or "hard finger".
• Annular fingeralso known as “fourth finger of the hand”; it is called annular for being the one bearing the wedding ring in Western culture.
• Fingering fingeralso known as "fifth finger of the hand" or "small finger of the hand".

The thumb

The first finger is the thumb (connected to the trapezium) it is on the outer side of the hand and it is in an anatomical position, parallel to the arm. The thumb can easily rotate 90º, perpendicular to the palm, unlike the rest of the fingers that can only rotate about 45º. A reliable way to recognize true hands in other (non-human) animals is to see if they have opposable thumbs. Opposable thumbs are differentiated by being able to oppose the rest of the fingers in a muscular action known as opposition. The other four fingers of the hand are located on the outer edge of the palm. These four fingers can be folded into the palm, this allows holding objects and also grasping smaller ones.

Bones

Hand bones

The human hand has 27 bones: the carpus or wrist has 8; the metacarpus or palm has 5 and the remaining 14 bones are digital.

Wrist Bones

The wrist has eight bones (the carpal bones), arranged in two groups of four. These bones fit into a small socket formed by the forearm, radius, and ulna bones, although it is noteworthy that the ulna does not articulate directly with any of the wrist bones. Under the underside of the ulna is the triangular ligament of the wrist, which does articulate with the bones.

• The bones of the proximal row are, from the outside to the inside: the scafoids, the semilunar, the pyramidal and the pisiform.
• The bones of the distal row are, from outside to inside: the trapezoid, the rag, the big and the hook.

Bones of the Palm

The palm of the hand has five bones (the metacarpal bones), one for each finger.

Digital Bones

Human hands contain fourteen digital bones, also called phalanges: two in the thumb, and three in each of the other four fingers; It is worth mentioning that the thumb does not have a middle phalanx.

The bones of the human hand are:

• distal phalanges
• Medium phalanges
• proximal phalanges

Hand Anatomy

Each hand has 27 bones, 8 in the carpus, 5 metacarpals, and a total of 14 phalanges. Together they form an anterior concavity channel through which the tendons of the flexor muscles of the fingers glide.

The eight carpal bones are arranged in two rows, one upper and one lower. From radial to ulnar the upper row consists of the scaphoid (scaphoideum), lunate (lunatum), triquetrum (triquetum ) and pisiform bones. The lower row is made up of the trapezium (trapecium), trapezoid (trapezoideum), large bone (capitatum) and hamate bone (amatum). ).

Except for the triquetrum, pisiform, and hamate bones, most of the carpal bones are cuboid in shape and have six faces.

The anterior and posterior faces are rough and correspond to the palmar and dorsal faces of the hand. The superior, inferior, and lateral or medial aspects are articular, except for the lateral aspects of the bones that are at the ends of both carpal rows.

Top Row

“Mano” Tupaia javanica compared to a human

Scaphoid bone: it is the most lateral, elongated from the top and bottom and from medial to lateral. They are described in it:

• Previous face: roary and prolonged by a scaphoid bone tuber, where the radial collateral ligament of the carpus is inserted.
• Later face: is narrow and reduced in a rough groove.
• Upper face: convex, joint and related to radio.
• Lower face: convex and joint for the trapezoid bones.
• Medium face: It has two joint surfaces: one upper, small and one lower more extensive.
• Side face: roaring and excavated by a groove.

Semilunar bone: Located between the scaphoid and the triquetrum.

• Previous face: convex and roar.
• Later face: almost flat and rough.
• Upper face: convex and is articulated with radio.
• Lower face: it is concave and joins the bone large laterally and medially with the hooked bone through a narrow surface.
• Medium face: joint with the pyramidal bone.
• Side face: joint with the scaphoid bone.

Pyramidal bone: It is shaped like a quadrangular pyramid.

• Previous face: has a somewhat convex joint surface for the pisiforme bone.
• Later face: presents a cross-sectional roaring slope, the crest of the pyramidal bone where a co-sided co-link of the carpo is inserted.
• Upper face: joint convex with the joint disc.
• Lower face: Concava, in connection to the hooked bone.
• Medial vertex: This vertex is rough.
• Side face (base): articulated with the semi-lunar bone.

Pisiform bone: irregularly rounded bone.

• Previous face: the insertion surface of the body's cubital flexor muscle at the top and the abducing muscle of the dye at the bottom.
• Later face: slightly concave, in connection with the previous face of the pyramidal bone.
• Side face: presents a shallow groove in relation to the cubital artery of the carpo.

Bottom Row

Trapezius bone: the most lateral of the second row.

• Previous face: it has a groove, laterally limited by an outgoing crest, called a trapeze bone tuber.
• Later face: roary, it has on its lateral and medial ends a tube for the insertion of ligaments.
• Upper face: Concava in relation to the scaphoid bone.
• Lower face: convex from prior to later. Articula with the first metacarpal bone.
• Medium face: it is in relation, through two different joint surfaces, with the trapezoid bone superiorly and the metacarpal bone lower in the second.
• Side face: it's rough.

Trapezoid bone: Located between the trapezoid bone and the capitate bone.

• Previous and rear face: rough.
• Upper face: it is concave and is articulated with the scaphoid bone.
• Lower face: joins the second metacarpal bone.
• Medium face: it is concave and is articulated with the big bone.
• Side face: is convex superior to inferior and concava from prior to later.

Large bone: It is the largest of the carpal bones. It describes a rounded upper part of the head, a body and an intermediate area called the neck.

• Previous face: it is rough
• Later face: is prolonged below by a slope: the apophysis of large bone.
• Upper face: convex and is articulated with the scaphoid and semi-lunar bones.
• Lower face: joint surface in which three juxtaposed ribs are distinguished for 2, 3 and 4 metacarpal bone.
• Medium face: it has a joint surface for the hooked bone.
• Side face: it is attached superiorly to the scaphoid bone and lower than the trapezoid bone.

Hamate bone: It has the shape of a triangular prism. It has five faces: two non-articular bases, one anterior and one posterior, and three articular faces.

• Previous face: presents a hook-shaped outlet.
• Later face: rough.
• Lower face it is articulated and is divided into two sides: one side and concave for the fourth metacarpal, and another medial, concava from previous to later and convex from side to side, for the fifth metacarpal.
• Superomedial face: convex superiorly and concave inferiorly, it is rough along its lower edge.
• Side face: it is articulated with the big bone.

Carpal bone massif. carpal canal and carpal canal

The eight carpal bones together form a bone mass that has four faces (anterior, posterior, superior and inferior) and two borders (lateral and medial).

Carpal canal: This canal is bounded laterally by the tubercles of the scaphoid and trapezius bones, and medially by the eminence of the pisiform bone and the hamate bone.

Carpal canal: through which the median nerve runs, and the tendons of the flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus muscles.

Metacarpus

It constitutes the skeleton of the palm and the back of the hand, it is made up of five long bones. The limited spaces between them are called interosseous spaces.

From lateral to medial, they are called the first, second, third, fourth, and fifth metacarpals.

A) Common characteristics of the metacarpal bones

There is a body and two ends: the base and the head of the metacarpal bone.

1. Body: describe an earlier concavity curve and has a triangular prismatic shape.

• • Later face: slightly convex, narrowly broad and sharper.
  • Two faces, side and side: they limit the interosian spaces and in which the interosic muscles are inserted.
  • Two edges, lateral and medial: more marked in the lower half than in the upper.
  • Previous era: concave.

2. Base: the upper base and cuboids.

• • Upper face: articulate in relation to the bones of the second carpo.
  • Two faces, side and side: joints, in connection with those of the neighboring metacarpals.
  • Dorsal and palmar face: presents roughness in which ligaments and muscles are inserted.

3. Head: represents the lower end of the metacarpal bone. It's flat from side to side.

• • Lower face: convex and articular, working with the base of the proximal falange.
  • Two faces, side and side: slightly depressed and above that of pressure, a tuber where collateral ligaments of the metacarpophalagic joint are inserted.
  • Dorsal face: rough.
  • Cara palmar: is largely occupied by the joint surface.

B) Some characteristics of each metacarpal bone

1. First metacarpal bone:

• • It's the shortest and most voluminous of all.
  • Its base does not have lateral and medial joint surfaces.

2. Second metacarpal bone:

• • It's the longest of all metacarpal bones.
  • The dorsal face of the base presents the styling apophysis of the second metacarpal bone.

3. Third and fourth metacarpal bone:

• • Each of the corresponding lateral or medial sides of the bases has joint surfaces.
  • The fourth metacarpal bone is much thinner than the third.

4. Fifth metacarpal bone:

• • Its base features a single side joint.
  • The medial rib of this base presents a tuber intended for the insertion of the cubital extending muscle of the body.

Therefore, and with all this, the wrist does not belong to the hand, but is a point of union between the hand and the forearm.

Phalanges

Each finger, with the exception of the thumb, consists of three bony segments: The phalanx. The thumb presents only two. They are designated by the names of proximal, middle and distal phalanx.

The phalanges are long bones, they have a body and two ends: the base and the head of the phalanx.

A) Proximal phalanx:

1. Body: is semi cylindrical, later convex and slightly concave earlier.
2. Base: presents a glynoid cavity for the head of the metacarpal and two palmare ribs for the sesamedium bones and two lateral tubers, determined for the insertion of the collateral ligaments of the metacarpo falangica joint.
3. Head: ends in a throcc related to the base of the medium falange. The joint surface extends widely over the palm face of the head.

B) Middle phalanx:

1. Body: it is similar to that of the proximal phalange.
2. Base: provided with a joint surface Formed by two side sides separated into a rhoma crest.
3. Head: presents the same configuration as that of the proximal falange.

C) Distal phalanx:

1. Body: it is very short, dorsally convex, and plane in its palm face.
2. Base: it is similar to that of the middle phalange.
3. Distal extreme: width and convex later, it has a rough and outgoing surface in the face of the palm.

D) Phalanx of the thumb:

1. Proximal Falange: similar to the other proximal phalangs of the other fingers.
2. Distal Falange: is analogous to the distal phalange.

However, the two phalanges of the thumb are larger than those of the other fingers.

Sesamoid Bones

The name sesamoid bones are given to small bones that have the shape of a sesame.

In the hand, there are a variable number of sesamoid bones, all located on the palmar side.

Two are constant and are found on the palmar aspect of the metacarpophalangeal joint of the index and little fingers. Less frequently, they are seen at the metacarpophalangeal joints of the middle and ring fingers and at the interphalangeal joint of the thumb. Other authors affirm^{[citation required]} that the only constant is the thumb. Those of the index and little finger are less constant but also usually appear. Less frequently than these are the metacarpophalangeal joints of the middle and ring fingers.

Variation, hand size

HandPaolo Monti.

The average length of an adult male hand is 175mm, while the average length of an adult female hand is 162mm. The mean hand width of adult men and women is 80 and 70 mm, respectively.

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 relationship is below 1 for both sexes, but it is lower in men than in women, on average.

Uses of the hands

The thumb in opposition to the other fingers allows to easily roast objects

The main use of the hands is to grasp and hold objects, although many more derive from these general uses, due to the great versatility of movement that the hand is capable of, as well as the precision it can achieve in these movements. Examples of uses of the hands are:

• The hands and fingers are primordial "utensils" in order to eat and drink.
• Hands are used in multiple customs, such as greeting (see handshake).
• With the hand you can gesticular, and there are even sign languages for communication with deaf people or with hearing problems. Some gestures can be especially obscene (depending on the country or scope), as it also occurs with verbal language, and an example is the fist with the extended heart finger, or with the extended index and finger.
• The hand also serves as a measure instrument. An extended hand is a palm, although its length is very variable according to the person.
• Individuals can use their hands as reading tools by writing in Braille. In this writing, the sensitivity of the fingers enters action as they must be able to feel the small grooves on the part of which it is composed.
• A closed hand is a fist, and can serve to hit or hold small objects. A closed hand with the extended index finger serves to point or touch something.
• You can also attach a pencil or other similar instrument to write or draw. Writing is an activity that really requires great precision and coordination of the different muscles and joints that make up the hand.
• Use them to communicate or relieve pain through massage techniques, also called "structured touch".
• Another use is to obtain or give physical pleasure.
• The hand has given rise to the right hand rulewhich is a practical agreement used in Physics and Mechanics.
• Due to the versatility of the hand movement, it can be used to interpret musical instruments.

Bone diseases

• Strange hand syndrome