The forearm is the region of the upper limb between the

elbow The elbow is the region between the 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 the m ...

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 biology concerned with the study of the 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 science, having it ...

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 th ...

, a word which is most often 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 c ...

that lies between the knee and the

ankle The ankle, or 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 ...

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: Recto ...

. The forearm contains two long bones, the radius and the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

, 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 * Interosseous ...

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 supinators that turn the hand to face down or upwards, respectively. In cross-section, the forearm can be divided into two fascial compartments. The posterior compartment contains the extensors of the hands, which are supplied by the radial nerve. 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 also runs the length of the forearm. The radial 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 not ...

, 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 co ...

. 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 blood sampling (also called '' phlebotomy'') or intravenous therapy. In healthcare, this procedure is performed by medical labo ...

, although the

cubital fossa The cubital fossa, chelidon, or elbow pit, is the triangular area on the anterior side of the upper limb between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (Latin ) when in standard anatomical position ...

is a preferred site for getting blood.

Structure

Bones and joints

The bones of the forearm are the radius (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 cupshaped depression on the head of the radius, and is limited ...

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 ligament ...

. Distally, it articulates with the ulna again at the distal radioulnar joint. 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 is ...

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 flake removed from a stone tool during the process of pressure flaking. In the Natufian period, a lu ...

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 that fits the trochlea of the humerus (the bone directly above the ulna in the arm) as part of the elbow jo ...

of the ulna articulates with the trochlea of the humerus and the radial notch articulates with the head of the radius at the

. Distally it forms part of the distal radioulnar joint 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 unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position ...

and

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

radioulnar joints (resulting in

pronation 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 ...

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 The fascial compartments of arm refers to the specific anatomical term of the compartments within the upper segment of the upper limb (the arm) of the body. The upper limb is divided into two segments, the arm and the forearm. Each of these ...

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 formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...

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, 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 C8 ...

(supplies FPL, lat. 1/2 of FDP, PQ). * Radial nerve – 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 The posterior interosseous nerve (or dorsal interosseous nerve) is a nerve in the forearm. It is the continuation of the deep branch of the radial nerve, after this has crossed the supinator muscle. It is considerably diminished in size compared t ...

and supplies muscles of the posterior compartment ( ED, EDM, ECU, APL,

EPB EPB of Chattanooga, formerly known as the Electric Power Board of Chattanooga, is an American electric power distribution and telecommunications company owned by the city of Chattanooga, Tennessee. EPB serves nearly 180,000 homes and businesses ...

, EPL, EI). * Ulnar nerve – 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 foss ...

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 f ...

***

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 The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It i ...

***

dorsal metacarpal artery The dorsal carpal arch (dorsal carpal network, posterior carpal arch) is an anatomical term for the combination (anastomosis) of dorsal carpal branch of the radial artery and the dorsal carpal branch of the ulnar artery near the back of the wrist ...

****

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 medial aspects of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins with the superficial branch of the radial ar ...

*** Anterior ulnar recurrent artery 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 be ...

* 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 (predicate logic), the set of tuples of values that satisfy the predicate * Ext ...

) 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 (which has two opposable thumbs on each " ...

rotates inwards (

pronated 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 ...

) and rotated back so that the palm rotates outwards ( supinated) due to movement at the elbow and the distal radioulnar joint.

Clinical significance

A fracture of the forearm can be classified as to whether it involves only the ulna ( ulnar fracture), only the radius ( radius fracture), 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 cortex on one side and remains intact on the oth ...

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 ( exostoses) in relation to the ends of long bones of the lower li ...

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