Extensor Region of the Forearm

Gross Anatomy


Extensor Region of the Forearm and Dorsum of the Hand



Anatomy Tables for Today's Topic

Bones of the Extensor Forearm Region
Muscles of the Extensor Forearm Region
Nerves of the Extensor Forearm Region
Arteries of Extensor Forearm Region
Joints of the Hand and Fingers
Joints and Ligaments of the Forearm
Fasciae of the Forearm


Bones of the Extensor Forearm Region

Bone Structure Description Notes
humerus   the bone of the arm (brachium) the humerus articulates proximally with the scapula at the glenoid fossa; it articulates distally with the radius and ulna at the elbow joint
lateral epicondyle a knob-like projection on the lateral side of the humerus proximal to the capitulum it is the site of attachment of the common extensor tendon which is the origin of several forearm extensor muscles (extensor carpi radialis brevis m., extensor digitorum m., extensor digiti minimi m. and extensor carpi ulnaris m.); inflammation of the attachment of the common extensor tendon is called lateral epicondylitis which is also known as "tennis elbow"
lateral supracondylar ridge a narrow ridge running proximally from the lateral epicondyle of the humerus it is the site of origin of the brachioradialis m. and the extensor carpi radialis longus m.
ulna   the bone on the medial side of the forearm (antebrachium) the ulna articulates proximally with the trochlea of the humerus and the head of the radius; it articulates distally with the ulnar notch of the radius
body the long slender midportion of the ulna it is also called the shaft or diaphysis; the interosseous membrane attaches to the entire length of the interosseous border of the body of the ulna
head the distal end of the ulna it is small and rounded for articulation with the radius
styloid process a small projection from the distal surface of the head of the ulna it is the site of attachment of the articular disk of the distal radioulnar joint
radius   the bone on the lateral side of the forearm (antebrachium) the radius pivots on its long axis and crosses the ulna during pronation
body the long, slender midportion of the radius it is also known as the shaft or diaphysis; the interosseous membrane attaches to the entire length of the body of the radius along its interosseous border; a fracture of the distal end of the body of the radius with a dorsal displacement of the distal fragment is quite common and is called a Colles' fracture
ulnar notch a shallow notch located on the medial surface of the distal end of the radius it articulates with the head of the ulna
styloid process the distal-most projection from the lateral side of the radius the radial styloid process projects lateral to the proximal row of carpal bones
carpal bones   the bones of the wrist eight bones arranged in two rows; a pneumonic for memorizing the carpal bones is " some lovers try positions that they can't handle" - the first letters of these eight words are the first letters of the names of the eight carpal bones arranged from lateral to medial, proximal row first: scaphoid, lunate, triquitrum, pisiform/trapezium, trapezoid, capitate, hamate
proximal row lateral to medial: scaphoid, lunate, triquetrum, pisiform the scaphoid and lunate bones of the proximal row articulate with the distal end of the radius
distal row lateral to medial: trapezium, trapezoid, capitate, hamate the distal row of carpal bones articulates with the metacarpal bones of the hand
metacarpal bones   the bones located between the carpal bones (wrist) and the phalanges (fingers) of the hand there are a total of five metacarpal bones in the hand; the metacarpals of digits 2-5 are bound together by ligaments to form a firm foundation for finger movements; the metacarpal of the thumb is more independent in its range of motion
base the proximal end of the metacarpal it articulates with the distal row of carpal bones
body the slender shaft of the metacarpal it is also known as the diaphysis
head the rounded distal end of the metacarpal it articulates with the proximal phalanx of the corresponding digit
phalanx (phalanges)   the distal two or three bones in the digits of the hand there are a total of 14 phalanges in the hand; the thumb has two phalanges (proximal and distal) and each of the other digits has three phalanges (proximal, middle and distal); phalanx means "line of soldiers"
base the proximal end of the phalanx the base of the proximal phalanx articulates with the head of the corresponding metacarpal bone; the base of the middle or distal phalanx articulates with the head of the next proximal phalanx
body the slender shaft of the phalanx also known as the diaphysis; the body of the distal phalanx is very short
head the distal end of the phalanx the proximal, middle and distal phalanges each have a head; the head of a proximal or middle phalanx articulates with the base of the next distal phalanx

Muscles of the Extensor Forearm Region

Muscle Origin Insertion Action Innervation Artery Notes
abductor pollicis longus middle one-third of the posterior surface of the radius, interosseous membrane, mid-portion of posterolateral ulna radial side of the base of the first metacarpal abducts the thumb at carpometacarpal joint radial nerve, deep branch posterior interosseous a. the tendons of abductor pollicis longus and extensor pollicis brevis make the lateral border of the anatomical snuffbox
brachioradialis upper two-thirds of the lateral supracondylar ridge of the humerus lateral side of the base of the styloid process of the radius flexes the elbow, assists in pronation & supination radial nerve radial recurrent a. although brachioradialis is innervated by the nerve for extensors (radial), its primary action is elbow flexion
extensor carpi radialis brevis lateral epicondyle of the humerus dorsum of the third metacarpal bone (base) extends the wrist; abducts the hand deep branch of radial nerve radial a. functions synergistically with the extensor carpi radialis longus and flexor carpi radialis in abduction of the hand
extensor carpi radialis longus lower one-third of the lateral supracondylar ridge of the humerus dorsum of the second metacarpal bone (base) extends the wrist; abducts the hand radial nerve radial a. functions synergistically with the extensor carpi radialis brevis and flexor carpi radialis in abduction of the hand
extensor carpi ulnaris common extensor tendon & the middle one-half of the posterior border of the ulna medial side of the base of the 5th metacarpal extends the wrist; adducts the hand deep branch of radial nerve ulnar a. functions synergistically with the flexor carpi ulnaris in adduction of the hand
extensor digiti minimi common extensor tendon (lateral epicondyle of the humerus) joins the extensor digitorum tendon to the 5th digit and inserts into the extensor expansion extends the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints of the 5th digit deep branch of radial nerve interosseous recurrent a. extensor digiti minimi appears to be the ulnar-most portion of extensor digitorum
extensor digitorum common extensor tendon (lateral epicondyle of the humerus) extensor expansion of digits 2-5 extends the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints of the 2nd-5th digits; extends wrist deep branch of radial nerve interosseous recurrent a. and posterior interosseous a. the extensor expansion inserts via a central band on the base of the middle phalanx, while lateral & medial slips insert on the distal phalanx
extensor indicis interosseous membrane and the posterolateral surface of the distal ulna its tendon joins the tendon of the extensor digitorum to the second digit; both tendons insert into the extensor expansion extends the index finger at the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints deep branch of radial nerve posterior interosseous a extensor indicis is a deep forearm extensor, whereas extensor digiti minimi is in the superficial layer of extensors
extensor pollicis brevis interosseous membrane and the posterior surface of the distal radius base of the proximal phalanx of the thumb extends the thumb at the metacarpophalangeal joint and secondarily extends the carpometcarpal joint of the thumb deep branch of radial nerve posterior interosseous a the tendons of extensor pollicis brevis and abductor pollicis longus make the lateral border of the anatomical snuffbox
extensor pollicis longus interosseous membrane and middle part of the posterolateral surface of the ulna base of the distal phalanx of the thumb extends the thumb at the interphalangeal joint and secondarily extends the carpometcarpal joint of the thumb deep branch of radial nerve posterior interosseous a the tendon of extensor pollicis longus hooks around the dorsal radial tubercle; it forms the medial border of the anatomical snuffbox
supinator lateral epicondyle of the humerus, supinator crest & fossa of the ulna, radial collateral ligament, annular ligament lateral side of proximal one-third of the radius supinates the forearm deep branch of radial nerve recurrent interosseous a. deep radial nerve passes through the supinator to reach the posterior compartment of the forearm

Nerves of the Extensor Forearm Region

Nerve Source Branches Motor Sensory Notes
antebrachial cutaneous, medial medial cord of the brachial plexus no named branches sympathetic motor innervation to skin skin of the medial side of the forearm medial antebrachial cutaneous nerve travels with the basilic vein for part of its course
antebrachial cutaneous, posterior radial n. inferior lateral brachial cutaneous n. sympathetic motor innervation to skin skin of the lateral distal arm and posterior forearm posterior antebrachial cutaneous n. passes posterior to the lateral epicondyle of the humerus
deep radial n. radial n. posterior interosseous n. extensor carpi radialis brevis m., supinator m., extensor digitorum m., extensor digiti minimi m., abductor pollicis longus m., extensor pollicis longus m. extensor pollicis brevis m., extensor indicis m. no cutaneous branches deep radial n. passes through the supinator m.; some authors consider the posterior interosseous n. and the deep radial n. to be synonymous, others consider the deep radial n. to become the posterior interosseous n. when it emerges from the supinator m. in the posterior forearm
dorsal branch of the ulnar n. ulnar n. dorsal digital sympathetic motor innervation to skin skin of the dorsal surface of the medial 1 1/2 digits; skin of the medial side of the back of the hand dorsal branch of the ulnar n. emerges at the level of the ulnar styloid process
digital, dorsal radial n. no named branches sympathetic motor innervation to skin dorsal skin of the lateral 3 1/2 digits, except the nail bed the nail bed is supplied by palmar digital nn.
radial n. posterior cord of the brachial plexus unnamed muscular branches, posterior brachial cutaneous n., inferior lateral brachial cutaneous n., posterior antebrachial cutaneous n., superficial and deep brs. muscles of the posterior arm: triceps brachii m., anconeus m.; muscles of the posterior forearm: brachioradialis, extensor carpi ulnaris m., extensor carpi radialis longus m., extensor carpi radialis brevis m., extensor digitorum m., extensor digiti minimi m., supinator m., abductor pollicis longus m., extensor pollicis longus m., extensor pollicis brevis m., extensor indicis m. skin of the posterior arm, forearm and hand all of the muscles on the posterior side of the arm and forearm are innervated by the radial n.
superficial radial n. radial n. dorsal digital brs. sympathetic motor innervation to skin skin of the posterolateral wrist and hand; dorsum of the lateral 3 1/2 digits (excluding the skin over the distal phalanx/nail bed) superficial radial n. is located deep to the brachioradialis muscle

Arteries of the Extensor Forearm Region

Artery Source Branches Supply to Notes
anterior interosseous common interosseous a. muscular brs.; a. of the median nerve flexor pollicis longus m., flexor digitorum profundus m., pronator quadratus m., radius, ulna, carpal bones anterior interosseous a. pierces the interosseous membrane at its distal end to reach the dorsal carpal anastomosis
anterior ulnar recurrent ulnar a. unnamed muscular brs. medial side of elbow and proximal ends of forearm flexor mm. anterior ulnar recurrent a. often arises in common with the posterior ulnar recurrent a.
common interosseous ulnar a. anterior interosseous a., posterior interosseous a. deep structures of the forearm common interosseous a. supplies the deep forearm flexor and deep forearm extensor muscles
dorsal carpal arterial arch radial a., ulnar a. dorsal metacarpal aa. dorsum of the hand and digits, excluding the distal phalangeal segment dorsal carpal arterial arch receives the majority of its blood supply from the radial a.
dorsal digital, of hand dorsal metacarpal a. no named branches dorsal aspect of 1/2 digit, excluding the distal phalangeal segment dorsal digital aa. do not supply the nail bed
dorsal metacarpal 1st: radial a.; 2-4: dorsal carpal arterial arch dorsal digital aa. (2) dorsum of 2 adjacent digits, excluding the distal phalangeal segment each dorsal metacarpal a. gives off a perforating br. that anastomoses with the deep palmar arterial arch
interosseous recurrent posterior interosseous a. unnamed muscular branches anconeus m., elbow joint interosseous recurrent a. anastomoses with the middle collateral a.
posterior interosseous common interosseous a. interosseous recurrent muscles of the posterior (extensor) forearm compartment: supinator m., abductor pollicis longus m., extensor pollicis longus m., extensor pollicis brevis m., extensor indicis m. posterior interosseous a. passes proximal to the interosseous membrane to reach the extensor compartment of the forearm
posterior ulnar recurrent ulnar a. unnamed muscular branches medial side of the elbow, forearm flexor mm. posterior ulnar recurrent a. often arises from a common trunk with the anterior ulnar recurrent a.
princeps pollicis radial a. two brs. to the thumb palmar aspect of the thumb including the dorsum of the distal phalangeal segment arteria princeps pollicis is similar in function to a proper digital a.
radial brachial a. radial recurrent a., palmar carpal br., superficial palmar br., dorsal carpal br., 1st dorsal metacarpal a., princeps pollicis a., radialis indicis a., deep palmar arterial arch posterior elbow, posterior forearm, posterior hand, deep portion of palmar side of the hand, thumb radial a. provides the majority of blood supply to the deep palmar arterial arch; normally it arises at the level of the elbow but may high branching of the brachial a. may result in the radial a. arising as proximal as the axilla
radial collateral deep brachial a. unnamed muscular branches lower lateral arm travels with the radial nerve; anastomoses with the radial recurrent a.
radial recurrent radial a. unnamed muscular branches lateral side of the elbow and adjacent extensor muscles radial recurrent a. anastomoses with the radial collateral a.; it courses in the groove between the brachioradialis m. and the brachialis m.
radialis indicis radial a. no named branches lateral (radial) side of the index finger arteria radialis indicis is equivalent to a proper digital a.
ulnar brachial a. unnamed muscular branches, anterior ulnar recurrent a., posterior ulnar recurrent a., common interosseous a., palmar carpal br., dorsal carpal br., deep palmar br., superficial palmar arterial arch medial side of the anterior forearm, posterior forearm, superficial palm, fingers ulnar a. is the primary contributor to the superficial palmar arterial arch; it normally arises at the level of the elbow, but high branching of the brachial a. may cause the ulnar a. to arise as far proximally as the axilla

Joints of the Hand and Fingers

Joint or ligament Description Notes
carpometacarpal joint, digits 2-5 the articulation between the distal carpal bones and the proximal ends of the metacarpal bones of the hand a synovial plane joint; limited motion is permitted at the carpometacarpal joint; the carpometacarpal joint is reinforced by dorsal and palmar ligaments
carpometacarpal joint, thumb the articulation between the trapezium and the proximal end of the metacarpal bone of the thumb a synovial saddle joint; this articulation permits two planes of motion: flexion/extension and abduction/adduction which may be combined to produce circumduction
interphalangeal joint the articulation between the proximal and middle phalanges (proximal interphalangeal joint, abbreviated PIP) or the middle and distal phalanges (distal interphalangeal joint, abbreviated DIP) a synovial hinge joint; this joint is strengthened by medial and lateral collateral ligaments
metacarpophalangeal joint the articulation between the head of a metacarpal and the base of a proximal phalanx a synovial condyloid (or ellipsoid) joint; it is strengthened by medial and lateral collateral ligaments; the joint has two planes of motion: flexion/extension and abduction/adduction which may be combined to yield circumduction

Joints and Ligaments of the Forearm

Joint or ligament Description Notes
interosseous membrane, forearm a fibrous membrane that connects the interosseous borders located on the shafts of the radius and the ulna a syndesmosis; its fibers are oriented obliquely downward from the radius toward the ulna; the interosseous membrane is the classic example of a syndesmosis; proximally directed forces from the hand pass through the radius and are transferred to the ulna through the interosseous membrane; marked proximally by the oblique cord

Fasciae of the Forearm

Structure Location/Description Notes
extensor retinaculum a thickening of the deep fascia on the dorsum of the wrist extensor retinaculum is attached to the bones of the dorsum of the wrist in several locations, resulting in compartments which separate and anchor the extensor tendons; tendons are surrounded by synovial tendon sheathes where they pass deep to retinacula



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Some of the material presented in these tables is contained in the book:
MedCharts Anatomy by Thomas R. Gest and Jaye Schlesinger
Published by ILOC, Inc., New York. Copyright 1995.

Content of tables edited for use in this course by Patrick W. Tank, Ph.D.
Copyright 2005, Department of Neurobiology and Developmental Sciences, University of Arkansas for Medical Sciences.

Unauthorized use is prohibited.