The structures lying in front of the conventional wrist from lateral to medial side are:
1. Radial artery.
2. Tendon of flexor carpi radialis (FCR).
3. Tendon of palmaris longus.
4. Flexor digitorum superficialis.
5. Ulnar artery.
6. Ulnar nerve.
7. Tendon of flexor carpi ulnaris.
Fig. 9.12 Branches of the median nerve in the forearm.
Pronator teres
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2. Abductor pollicis longus (APL).
3. Extensor pollicis brevis (EPB).
4. Extensor pollicis longus (EPL).
5. Extensor indicis.
The three deep extensors of the forearm, which act on thumb (abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus) lie deep to the superficial extensors and in order to gain insertion on the three short long bones of thumb ‘crop out’ (emerge) from the furrow in the lateral part of the forearm between lateral and posterior groups of superficial extensor. These three muscles are therefore termed outcropping muscles.
The origin, insertion, nerve supply, and actions of deep muscles of the back of forearm are presented in Table 9.2.
N.B.
• None of the deep muscles of the back of forearm cross the elbow joint.
• All of them arise from the radius, ulna, and interosseous membrane.
• All of them are supplied by the posterior interosseous nerve (deep branch of the radial nerve).
Fig. 9.14 Arrangement of the superficial muscles on the back of the forearm.
Common extensor origin
Brachioradialis
Extensor carpi radialis longus
Extensor carpi radialis brevis
Abductor pollicis longus
Outcropping muscles Extensor pollicis
brevis
Extensor pollicis longus
Lateral group of superficial extensors
Anconeus Extensor carpi ulnaris
Extensor digiti minimi
Extensor digitorum
Lister’s tubercle Posterior group of
superficial extensors
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Table 9.1 Origin, insertion, nerve supply, and actions of the superficial muscles of the back of the forearm (superficial extensors)
Muscle Origin Insertion Nerve supply Actions
Lateral group Brachioradialis
(Fig. 9.15)
Upper two-third of the lateral supracondylar ridge of the humerus
Lateral surface of the distal end of radius just above the styloid process
Radial nerve • Flexes the elbow joint.
• Pronates the supinated forearm to midprone position
• Supinates the pronated forearm to midprone position
Extensor carpi radialis longus (ECRL)
Lower one-third of the lateral supracondylar ridge of the humerus
Lateral side of the dorsal surface of the base of second metacarpal bone
Radial nerve • Acting with extensor carpi ulnaris extends the wrist
• Acting with flexor carpi radialis abducts the wrist
Extensor carpi radialis brevis (ECRB)
By a common tendon from the lateral epicondyle of the humerus and lateral ligament of the elbow joint
Lateral side of the dorsal surface of the base of third metacarpal bone
Posterior interosseous nerve before piercing the supinator
-do-Posterior group Extensor digitorum By a common tendon from
the lateral epicondyle
• Gives rise to four tendons for medial four digits.
• By the extensor expansion it is inserted into the dorsum of middle and terminal phalanges
Posterior interosseous nerve
Extends the medial four digits. Can also extend the wrist
Extensor digiti minimi By the common tendon from the lateral epicondyle
• Lies medial to the extensor digitorum tendon for the little finger.
• Through the extensor expansion, it is inserted into the dorsum of middle and terminal phalanges of little finger
Posterior interosseous
Extensor carpi ulnaris (ECU)
By the common tendon from the lateral epicondyle and by an aponeurosis from the upper two-third of the posterior border of ulna along with flexor carpi ulnaris and flexor
digitorum profundus
Into a tubercle on the medial side of the dorsal surface of the base of the fifth metacarpal
Posterior interosseous nerve
• Acting with extensor carpi radialis it extends the wrist
• Acting with flexor carpi ulnaris it adducts the wrist
Anconeus From the back of the lateral epicondyle
Lateral side of the olecranon process and upper one-fourth of the posterior surface of the ulna
Nerve to anconeus, which arises from radial nerve in spiral groove and descends through medial head of the triceps brachii
Weak extensor of the elbow joint
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Fig. 9.15 Origin and insertion of the brachioradialis.
BRACHIORADIALIS
Insertion Lateral side of distal end of radius just above the styloid process Origin Upper 2/3rd of lateral supracondylar ridge
Fig. 9.16 Lateral aspect of the lower end of humerus showing origin of seven superficial muscles of the back of forearm (ECRB = extensor carpi radialis brevis, ED = extensor digitorum, EDM = extensor digiti minimi, ECU = extensor carpi ulnaris).
Brachioradialis
Brachialis
Anconeus
Extensor carpi radialis longus
Common extensor origin (ECRB, ED, EDM, and ECU)
Fig. 9.17 Insertion of the extensor carpi ulnaris, extensor carpi radialis longus, and extensor carpi radialis brevis.
Extensor carpi radialis longus (ECRL) inserts on the dorsal aspect of the base of 2nd metacarpal
Extensor carpi ulnaris (ECU) insets on the medial side of the base of 5th metacarpal
Extensor carpi radialis brevis (ECRB) insets on the bases of 2nd and 3rd metacarpals
First metacarpal Fifth metacarpal
Lister’s tubercle
Tendon of extensor indicis Tendon of
extensor carpi ulnaris Proximal
phalanx Middle phalanx Distal phalanx
Tendon of extensor digitorum
Fig. 9.18 Insertion of the extensor digitorum, extensor carpi ulnaris, and extensor indicis.
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Table 9.2 Origin, insertion, nerve supply, and actions of the deep muscles of the back of the forearm (deep extensors of forearm)
Muscle Origin Insertion Nerve supply Action
Supinator (Fig. 9.20) • Lateral epicondyle
• Lateral ligament of the elbow joint
• Annular ligament
• Supinator crest of ulna and from the
triangular area in front of it
Upper one-third of the posterior, lateral, and anterior surfaces of the radius
Posterior interosseous nerve before piercing the supinator
Supination of the forearm
Abductor pollicis longus (APL)
• Lateral part of the posterior surface of ulna below the anconeus
• Middle one-third of the posterior surface of radius (below the posterior oblique line) and intervening posterior surface of interosseous membrane
Lateral side of the base of first metacarpal posterior surface of radius below the origin of abductor pollicis longus and from adjoining interosseous membrane
Dorsal surface of the base of proximal phalanx of thumb
Posterior interosseous nerve
Extends the thumb at metacarpophalangeal joint and extends the carpometacarpal joint
Extensor pollicis longus From lateral part of middle one-third of the posterior surface of ulna and adjoining
interosseous membrane
Dorsal surface of the base of distal phalanx of thumb
Extensor indicis From the posterior surface of ulna below the origin of extensor pollicis longus and also from the adjoining interosseous membrane
• The tendon lies medial to the extensor digitorum tendon for the index finger
• Through the extensor expansion, it is inserted into the dorsum of middle and distal phalanges of the index finger
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S
APL
Radius Ulna
EPL EPB EI
Fig. 9.19 A, Origin of five deep muscles of the back of forearm from the posterior aspects of radius and ulna (S = supinator, APL = abductor pollicis longus, EPL = extensor pollicis longus, EPB = extensor pollicis brevis, EI = extensor indicis); B, Origin and insertion of the deep muscles on the back of the forearm (L = Lister’s tubercle).
Extensor pollicis longus Insertion
Supinator Upper 1/3rd of the lateral
surface of radius Origin Supinator Supinator crest of ulna
Extensor indicis
Insertions Abductor pollicis longus
↓
Radial side of base of 1st metacarpal Extensor pollicis brevis
↓
Base of proximal phalanx of thumb Extensor pollicis longus
↓
Base of distal phalanx of thumb Extensor indicis
↓
Ulnar side of extensor digitorum tendon for index finger Extensor pollicis longus
↓
1. Posterior surface of ulna 2. Interosseous membrane
Extensor pollicis brevis Abductor pollicis longus
Origins Abductor pollicis longus
↓ 1. Post surface of ulna 2. Interosseous membrane 3. Posterior surface of radius
L
1. Post surface of ulna
2. Adjoining part of interosseous membrane
Extensor indicis
↓
Extensor pollicis brevis
↓
1. Posterior surface of radius 2. Interosseous membrane
A B
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Fig. 9.20 Origin and insertion of the supinator muscle.
Fig. 9.21 Extensor retinaculum.
Origin (contd) 4. Supinator crest 5. Adjoining part of triangular area SUPINATOR
Insertion
Upper 1/3rd of lateral surface of radius
Origin
1. Lateral epicondyle of humerus
2. Radial collateral ligament 3. Annular ligament
Fig. 9.22 Transverse section of the forearm just above the wrist showing structures passing deep to the extensor retinaculum.
Extensor carpi radialis brevis Extensor pollicis longus
Extensor carpi radialis longus