MUSCLES OF THE POSTERIOR COMPARTMENT
OF FOREARM AND EXTENSOR RETINACULUM
Learning Objectives
At the end of lecture, students will be able to understand:
• The concept of the muscles of posterior compartment of forearm
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The nerve supply of these muscles
The actions of the muscles of posterior compartment of forearm
Extensor Retinaculum
Muscles of Posterior Compartment of Forearm
1. Anconeus.
2.Supinator.
3.Brachioradialis.
4.Extenser carpi radialis longus.
5.Extenser carpi radialis brevis.
6.Extensor digitorium.
7.Extensor digiti minimi.
8.Extensor carpi ulnaris
9.Abductor pollicis longus.
10. Extensor pollicis longus.
11. Extensor pollicis brevis
12.Extensor indices
Muscles of Forearm
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Cross Wrist = flex, extend, abduct, adduct hand
Cross Fingers = flex, extend fingers
Most muscles fleshy proximally, long tendons distally
Flexor + Extensor Retinacula
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– wristbands keep tendons from bowing
– thick, deep fascia
Posterior Extensor Compartment (Superficial + Deep layers)
– Innervated by Radial nerve (or branches of radial nerve)
BRACHIORADIALIS
Origin:
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Upper two third of supracondylar ridge.
Insertion:
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Styloid process of radius.
Action:
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flexion at elbow joint.
Nerve supply:
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Radial nerve
COMMON EXTENSOR ORIGIN
• Arise from smooth area in front of the lateral epicondyle of humerus.
• This fused tendon gives rise to:
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Extensor carpi radialis brevis.
Extensor digitorum.
Extensor digiti minimi.
Extensor carpi ulnaris.
EXTENSER CARPI RADIALIS LONGUS
Origin:
• Lower third of the lateral supra-condylar ridge of humerus.
Insertion:
• Base of second metacarpal
Action:
• Extensor and abductor of wrist
Nerve supply:
• Radial nerve
EXTENSOR CARPI RADIALIS BREVIS
Origin: Common extensor origin.
Insertion:
• Base of third metacarpal.
Nerve supply:
• Radial nerve
Action:
• Wrist extensor
EXTENSOR DIGITORUM
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Origin:
common extensor origin
Insertion:
middle and distal phalanges of medial four fingers.
Action:
Extensor of the wrist, metacarpophalangeal joint and interphalangeal joints.
Nerve supply:
Radial nerve
EXTENSOR DIGITI MINIMI
• Origin:
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common extensor origin
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Insertion:
• extensor expansion of distal phalanx of little finger.
• Action:
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Assists extensor digitorum with extension of wrist and little finger.
• Nerve supply:
• Radial nerve.
EXTENSOR CARPI ULNARIS
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Origin:
Arises from the common extensor origin.
Insertion: into the base of 5th metacarpal.
Nerve supply: Radial nerve.
Action: Extends and adducts hand at wrist joint.
ANCONEUS
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Origin:
posterior surface of lateral epicondyle of humerus.
Insertion: lateral side of olecronon and adjacent shaft of the ulna.
Nerve supply: Radial nerve.
Action: Extends elbow joint
SUPINATOR
• Origin:
• lateral epicondyle of humerus and annular ligament of superior radioulnar joint.
Insertion:
• Neck and shaft of radius.
• Action:
• Supination of forearm.
• Nerve supply: Radial nerve
ABDUCTOR POLLICIS LONGUS
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Origin: Shaft of radius and ulna.
Insertion: Base of first metacarpal.
Action: Abduct and extend thumb.
Nerve supply:Radial nerve.
EXTENSOR POLLICIS BREVIS
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Origin:
Shaft of radius and interosseus membrane.
Insertion: Base of proximal phalanx of thumb.
Nerve supply:
Radial nerve.
Action: Extends MCP joints of thumb.
EXTENSOR POLLICIS LONGUS
• Origin: Shaft of ulna and interosseus membrane.
• Insertion:Into the base of distal phalanx of thumb.
• Action: Extends distal phalynx of thumb.
• Nerve supply: Radial nerve.
EXTENSOR INDICIS
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Origin: Shaft of ulna and interosseus membrane.
Insertion: Extensor expansion of index finger.
Action: Extends MCP joint of index finger.
ANATOMICAL SNUFFBOX
• Anatomical snuffbox lies between extensor pollicis longus tendon on
ulnar side and tendons of extensor pollicis brevis and abductor pollicis
longus on radial side.
EXTENSOR RETINACULUM
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A band like thickening in the deep fascia of forearm.
About 2.5 cm wide.
Passes obliquely across the extensor surface of wrist.
Attached on radius above the styloid process to the pisiform and triquetral bones.
CARPAL TUNNEL
• Extensor carpal tunnel is divided in to six compartments by fibrous septa passing to
bones of forearm
Starting from lateral side
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First compartment lying over lateral surface of the radius at its distal extremity,
tendons of abductor pollicis longus and extensor pollices brevis pass through. Each
has separate synovial sheath.
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Next compartment extends as far as dorsal tubercle, giving passage to extensor of
wrist i.e. longus and brevis. Each lying in separate synovial sheath.
• Groove on the ulnar side of the radial tubercle lodges tendon of extensor pollicis longus. Invested with
synovial sheath.
• Next compartment lodges extensor digitorium tendons crowded together over indices tendon.
Invested by common synovial sheath.
• Over radioulnar joint tendons of extensor digiti minimi (in a synovial sheath) pass.
• Groove near ulnar styloid transmits tendon of extensor carpi ulnaris in its synovial sheath.