The forearm is the region of the upper limb between the elbow and the wrist. 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 i ...

to distinguish it from the arm, 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 that lies between the knee and the ankle 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

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 (plural, : radii) 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 name comes from the latin ''radius'', ...

and the ulna, 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 wrist, 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, 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, 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

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

Radius

Proximally, the head of the radius articulates with the capitulum of the humerus and the radial notch of the ulna at the elbow. 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 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 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 of the ulna articulates with the trochlea of the humerus and the radial notch articulates with the head of the radius at the elbow. Distally it forms part of the distal radioulnar joint and also articulates with the wrist.

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 radioulnar joints (resulting in pronation or supination, 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.

Nerves

:''See separate nerve articles for details on divisions proximal to the elbow and distal to the wrist; see Brachial plexus 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 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, 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 *** dorsal metacarpal artery **** Princeps pollicis artery ** Ulnar artery *** 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 **** Posterior interosseous artery **** Anterior interosseous artery

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 elbow. The forearm can also be rotated so that the palm of the hand 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 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 Standard anatomical position, anatomical position, is found on the Medial (anatomy), medial side of the forear ...

), 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 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