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, 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. 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 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), and pronators 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 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, 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 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. Distally, it articulates with the ulna again at the distal radioulnar joint. It forms part of the wrist joint by articulating with the scaphoid 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 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 and distal radioulnar joints (resulting in pronation or

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 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, PL, FDS). ** anterior interosseous nerve (supplies FPL, lat. 1/2 of FDP, PQ). * Radial nerve – supplies muscles of the posterior compartment ( ECRL, ECRB). ** Superficial branch of radial nerve ** Deep branch of radial nerve, becomes Posterior interosseus nerve and supplies muscles of the posterior compartment ( ED, EDM, ECU, APL, EPB, 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 fossa ...

** Radial artery *** Radial recurrent artery *** dorsal metacarpal artery **** Princeps pollicis artery ** Ulnar artery *** Anterior ulnar recurrent artery and posterior ulnar recurrent artery *** Common interosseous artery **** Posterior interosseous artery **** Anterior interosseous artery

Other structures

* Interosseous membrane of forearm * Annular ligament of ulna

Function

The forearm can be brought closer to the upper arm ( flexed) and brought away from the upper arm ( extended) 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) due to movement at the elbow and the distal radioulnar joint.

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), or both radioulnar fracture. For treatment of children with torus fractures of the forearm splinting appears to work better than casting. Genetically determined disorders like hereditary multiple exostoses 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