The forearm is the region of the

upper limb The upper Limb (anatomy), limbs or upper extremities are the forelimbs of an upright posture, upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digit (anatomy), digits, including all the musc ...

between the

elbow The elbow is the region between the upper arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa (also called the chelidon, or the elbow pit), and the lateral and t ...

and the

wrist In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...

. The term forearm is used in

anatomy Anatomy () is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old scien ...

to distinguish it from the

arm In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between ...

, a word which is used to describe the entire appendage of the upper limb, but which in anatomy, technically, means only the region of the upper arm, whereas the lower "arm" is called the forearm. It is homologous to the region of the

leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element cap ...

that lies between the

knee In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...

and the

ankle The ankle, the talocrural region or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joint. The ...

joints, the

crus Crus can refer to: *''Crus'', a subgenus of the fly genus ''Metopochetus'' *Crus (lower leg) *Crus, a plural of Cru (wine) *CRUs, an abbreviation of Civil Resettlement Units * Rektorenkonferenz der Schweizer Universitäten (CRUS; English: Rectors ...

. The forearm contains two long

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

s, the

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

and the

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

, forming the two radioulnar joints. The

interosseous membrane An interosseous membrane is a thick dense fibrous sheet of connective tissue that spans the space between two bones, forming a type of syndesmosis joint. Interosseous membranes in the human body: * Interosseous membrane of forearm * Interosseo ...

connects these bones. Ultimately, the forearm is covered by skin, the anterior surface usually being less hairy than the posterior surface. The forearm contains many muscles, including the flexors and extensors of the

, flexors and extensors of the digits, a flexor of the elbow (

brachioradialis The brachioradialis is a muscle of the forearm that flexes the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm. It is attached to the distal styloid process of the radius by way ...

), and

pronator Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

s and

supinator In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius (bone), radius. Its function is to supination, supinate the forearm. Structure The supinator consists of tw ...

s that turn the hand to face down or upwards, respectively. In cross-section, the forearm can be divided into two

fascial compartment A fascial compartment is a section within the body that contains Skeletal muscle, muscles and nerves and is surrounded by deep fascia. In the human body, the Limb (anatomy), limbs can each be divided into two segments – the upper limb can be di ...

s. The posterior compartment contains the extensors of the hands, which are supplied by the

radial nerve The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the Posterior compartment of the ...

. The anterior compartment contains the flexors and is mainly supplied by the

median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has cont ...

. The flexor muscles are more massive than the extensors because they work against gravity and act as anti-gravity muscles. The

ulnar nerve The ulnar nerve is a nerve that runs near the ulna, one of the two long bones in the forearm. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or ...

also runs the length of the forearm. The

radial Radial is a geometric term of location which may refer to: Mathematics and Direction * Vector (geometric), a line * Radius, adjective form of * Radial distance (geometry), a directional coordinate in a polar coordinate system * Radial set * A ...

and ulnar arteries and their branches supply the blood to the forearm. These usually run on the anterior face of the radius and ulna down the whole forearm. The main superficial veins of the forearm are the

cephalic A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may no ...

, median antebrachial and the

basilic vein The basilic vein is a large superficial vein of the upper limb that helps drain parts of the hand and forearm. It originates on the medial ( ulnar) side of the dorsal venous network of the hand and travels up the base of the forearm, where its ...

. These veins can be used for cannularisation or

venipuncture In medicine, venipuncture or venepuncture is the process of obtaining intravenous access for the purpose of venous Sampling (medicine)#blood, blood sampling (also called ''phlebotomy'') or intravenous therapy. In healthcare, this procedure is p ...

, although the

cubital fossa The cubital fossa, antecubital fossa, chelidon, inside of elbow, or, humorously, wagina, is the area on the anterior side of the upper part between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (antecubit ...

is a preferred site for getting blood.

Structure

Bones and joints

The bones of the forearm are the

(located on the lateral side) and the

(located on the medial side) Radius and Ulna - Forearm Bones

Radius

Proximally, the head of the radius articulates with the

capitulum of the humerus In human anatomy of the arm, the capitulum of the humerus is a smooth, rounded eminence on the lateral portion of the distal articular surface of the humerus. It articulates with the cup-shaped depression on the head of the radius, and is limi ...

and the radial notch of the ulna at the

. The articulation between the radius and the ulna at the elbow is known as the

proximal radioulnar joint The proximal radioulnar articulation, also known as the proximal radioulnar joint (PRUJ), is a synovial pivot joint between the circumference of the head of the radius and the ring formed by the radial notch of the ulna and the annular ligamen ...

. Distally, it articulates with the ulna again at the

distal radioulnar joint The distal radioulnar articulation (also known as the distal radioulnar joint, or inferior radioulnar joint) is a synovial pivot joint between the two bones in the forearm; the radius and ulna. It is one of two joints between the radius and ulna ...

. It forms part of the

wrist joint In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...

by articulating with the

scaphoid The scaphoid bone is one of the carpal bones of the wrist. It is situated between the hand and forearm on the thumb side of the wrist (also called the lateral or radial side). It forms the radial border of the carpal tunnel. The scaphoid bone ...

at its lateral aspect and with the

lunate Lunate is a crescent or moon-shaped microlith. In the specialized terminology of lithic reduction, a lunate flake is a small, crescent-shaped lithic flake, flake removed from a stone tool during the process of pressure flaking. In the Natufian cu ...

at its medial aspect.

Ulna

Proximally, the

trochlear notch The trochlear notch (), also known as semilunar notch and greater sigmoid cavity, is a large depression in the upper extremity of the ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to ...

of the ulna articulates with the

trochlea of the humerus In the human arm, the humeral trochlea is the medial portion of the articular surface of the elbow joint which articulates with the trochlear notch on the ulna in the forearm. Structure In humans and other apes, it is trochleariform (or trochlei ...

and the

radial notch The radial notch of the ulna (lesser sigmoid cavity) is a narrow, oblong, articular depression on the lateral side of the coronoid process; it receives the circumferential articular surface of the head of the radius. It is concave from before b ...

articulates with the head of the radius at the

. Distally it forms part of the

and also articulates with the

Muscles

* "E/I" refers to "extrinsic" or "intrinsic". The intrinsic muscles of the forearm act on the forearm, meaning, across the elbow joint and the

proximal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

and

distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...

radioulnar joints (resulting in

pronation Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

supination Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

), whereas the extrinsic muscles act upon the hand and wrist. In most cases, the extrinsic anterior muscles are ''flexors'', while the extrinsic posterior muscles are ''extensors''. * The brachioradialis, flexor of the forearm, is unusual in that it is located in the posterior compartment, but it is actually in the anterior portion of the forearm. * The

anconeus The anconeus muscle (or anconaeus/anconæus) is a small muscle on the posterior aspect of the elbow joint. Some consider anconeus to be a continuation of the triceps brachii muscle. Some sources consider it to be part of the posterior compartment ...

is considered by some as a part of the

posterior compartment of the arm Posterior may refer to: * Posterior (anatomy), the end of an organism opposite to anterior ** Buttocks, as a euphemism * Posterior horn (disambiguation) * Posterior probability The posterior probability is a type of conditional probability that ...

Nerves

:''See separate nerve articles for details on divisions proximal to the elbow and distal to the wrist; see

Brachial plexus The brachial plexus is a network of nerves (nerve plexus) formed by the anterior rami of the lower four Spinal nerve#Cervical nerves, cervical nerves and first Spinal nerve#Thoracic nerves, thoracic nerve (cervical spinal nerve 5, C5, Cervical spi ...

for the origins of the median, radial and ulnar nerves.'' *

Median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has cont ...

– interior nerve of the anterior compartment ( PT,

FCR FCR may refer to: Science and medicine * Fc receptor * Fire-cracked rock * Flexor carpi radialis muscle * Folin–Ciocalteu reagent *Fuji computed radiography, name of a series of computed radiography systems made by Fujifilm Sport * FCR 2001 ...

, PL, FDS). **

anterior interosseous nerve The anterior interosseous nerve (volar interosseous nerve) is a branch of the median nerve that supplies the deep muscles on the anterior of the forearm, except the ulnar (medial) half of the flexor digitorum profundus. Its nerve roots come from C ...

(supplies FPL, lat. 1/2 of FDP, PQ). *

Radial nerve The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the Posterior compartment of the ...

– supplies muscles of the posterior compartment ( ECRL, ECRB). **

Superficial branch of radial nerve The superficial branch of the radial nerve passes along the front of the radial side of the forearm to the commencement of its lower third. It is a sensory nerve. It lies at first slightly lateral to the radial artery, concealed beneath the brac ...

Deep branch of radial nerve The radial nerve divides into a superficial (sensory) and deep (motor) branch at the cubital fossa. The deep branch of the radial nerve winds to the back of the forearm around the lateral side of the radius between the two planes of fibers of the s ...

, becomes Posterior interosseus nerve and supplies muscles of the posterior compartment ( ED, EDM, ECU, APL, EPB, EPL, EI). *

Ulnar nerve The ulnar nerve is a nerve that runs near the ulna, one of the two long bones in the forearm. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or ...

– supplies some medial muscles ( FCU, med. 1/2 of FDP).

Vessels

Brachial artery The brachial artery is the major blood vessel of the (upper) arm. It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa ...

Radial artery In human anatomy, the radial artery is the main artery of the lateral aspect of the forearm. Structure The radial artery arises from the bifurcation of the brachial artery in the antecubital fossa. It runs distally on the anterior part of the ...

***

Radial recurrent artery The radial recurrent artery arises from the radial artery immediately below the elbow. It ascends between the branches of the radial nerve, lying on the supinator muscle and then between the brachioradialis muscle and the brachialis muscle, suppl ...

*** dorsal metacarpal artery ****

Princeps pollicis artery The princeps pollicis artery, or principal artery of the thumb, arises from the radial artery just as it turns medially towards the deep part of the hand; it descends between the first dorsal interosseous muscle and the oblique head of the adduct ...

Ulnar artery The ulnar artery is the main blood vessel, with oxygenated blood, of the Human Anatomical Terms#Anatomical directions, medial aspects of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins ...

***

Anterior ulnar recurrent artery The anterior ulnar recurrent artery is an artery in the forearm. It is one of two recurrent arteries that arises from the ulnar artery, the other being the posterior ulnar recurrent artery. It arises from the ulnar artery immediately below the el ...

and

posterior ulnar recurrent artery The posterior ulnar recurrent artery is an artery in the forearm. It is one of two recurrent arteries that arises from the ulnar artery, the other being the anterior ulnar recurrent artery. The posterior ulnar recurrent artery being much larger t ...

***

Common interosseous artery The common interosseous artery, about 1 cm. in length, arises immediately below the tuberosity of the radius from the ulnar artery. Passing backward to the upper border of the interosseous membrane An interosseous membrane is a thick den ...

****

Posterior interosseous artery The posterior interosseous artery (dorsal interosseous artery) is an artery of the forearm. It is a branch of the common interosseous artery, which is a branch of the ulnar artery. Structure The posterior interosseous artery passes backward bet ...

****

Anterior interosseous artery The anterior interosseous artery (volar interosseous artery) is an artery in the forearm. It is a branch of the common interosseous artery. Course It passes down the forearm on the palmar surface of the interosseous membrane. It is accompanied ...

Other structures

Interosseous membrane of forearm The interosseous membrane of the forearm (rarely middle or intermediate radioulnar joint) is a fibrous sheet that connects the interosseous margins of the radius and the ulna. It is the main part of the radio-ulnar syndesmosis, a fibrous joint ...

* Annular ligament of ulna

Function

The forearm can be brought closer to the upper arm ( flexed) and brought away from the upper arm (

extended Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (proof theory) * Extension (predicate logic), the set of tuples of values that ...

) due to movement at the

. The forearm can also be rotated so that the palm of the

hand 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#Characteristics, koala (which has two thumb#O ...

rotates inwards ( pronated) and rotated back so that the palm rotates outwards (

supinated Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relati ...

) due to movement at the elbow and the

Clinical significance

fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...

of the forearm can be classified as to whether it involves only the ulna ( ulnar fracture), only the radius (

radius fracture The radius or radial bone (: radii or radiuses) is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is longer ...

), or both radioulnar fracture. For treatment of children with

torus fracture A Torus fracture, also known as a buckle fracture is the most common fracture in children. It is a common occurrence following a fall, as the wrist absorbs most of the impact and compresses the bony Cortical bone, cortex on one side and remains int ...

s of the forearm splinting appears to work better than casting. Genetically determined disorders like

hereditary multiple exostoses Hereditary multiple osteochondromas (HMO), also known as hereditary multiple exostoses, is a disorder characterized by the development of multiple benign osteocartilaginous masses (exostosis, exostoses) in relation to the ends of long bones of t ...

can lead to hand and forearm deformities. Hereditary multiple exostoses is due growth disturbance of the epiphyses of the radius and ulna, the two bones of the forearm.

Additional images

References

{{Authority control Upper limb anatomy

Structure

Bones and joints

Radius

Ulna

Muscles

Nerves

Vessels

Other structures

Function

Clinical significance

Additional images

See also

References