Anatomy of the posterior compartment of the forearm Flashcards
What are the muscles found in the posterior compartment of the forearm?
1) Brachioradialis (arises from the humerus and does not have an action of the wrist)
2) Extensor carpi radialis longus (ECRL)
3) Extensor carpi radialis brevis (ECRB)
4) Extensor digitorum
5) Extensor digiti minimi (EDM)
6) Extensor carpi ulnaris
7) Anconeus
- Important in moving the elbow and wrist joint
- Except for 1, 2 & 7 all of them arise from the common extensor origin
Why is the brachioradialis considered from the posterior aspect and not the anterior?
Its arrangement/location is in the dorsal aspect of the forearm its tendon runs on the dorsal aspect of the forearm
Which muscles are superficial in the posterior compartment of the hand?
1) Brachioradialis
2) Extensor carpi radialis longus
3) Extensor carpi radialis brevis
4) Extensor digiti minimi
5) Extensor carpi ulnaris
6) Extensor digitorum
What is the origin of the brachoradialis muscle?
Upper 2/3 of the lateral supracondylar ridge, in front of the lateral intermuscular septum
Where does the brachoradialis insert?
The lateral side of the lower end of the radius, above the styloid process
Which nerve supplies the brachoradialis?
Radial nerve (along with longus & anconeus)
What is the action of brachoradialis?
1) Initiation of supination & pronation (rotates the supinated/pronated forearm to the mid-prone position)
2) Flexion of the elbow joint mid-prone position
What is the origin of the extensor carpi radialis longus?
1) Lower 1/3 of the lateral supracondylar ridge, in front of the lateral intermuscular septum
(Not from the common extensor origin)
Where is the extensor carpi radialis longus?
Dorsum of the base of the 2nd metacarpal bone
What is the nerve supply of the extensor carpi radialis longus muscle?
Radial nerve
What is the action of the extensor carpi radialis longus muscle?
Extension and abduction of the hand at the wrist joint
What is the origin of the extensor carpi radialis brevis?
The common extensor origin (in front of the lateral epicondyle of the humerus) (the common extensor origin will give all posterior muscles except the brachioradialis and anconeus)
Where does the extensor carpi radialis brevis insert?
Dorsum of the base of the 3rd metacarpal bone
What is the nerve supply of the extensor carpi radialis brevis?
Posterior interosseous nerve
What is the action of the extensor carpi radialis brevis?
1) Extension of the hand and wrist joint
2) Abduction of the hand and the wrist joint
What is the origin of the extensor carpi ulnaris?
Common extensor origin (front of the lateral epicondyle of the humerus)
Where does the extensor carpi ulnaris insert?
Dorsum of the base of the 5th metacarpal bone
What is the nerve supply of the extensor carpi ulnaris?
Posterior interosseous nerve
What is the action of the extensor carpi ulnaris?
1) Extension of the hand and wrist joint
2) Adduction of the hand and wrist joint
What is the origin of the extensor digitorum?
Common extensor origin (front of the lateral epicondyle of the humerus)
Where does the extensor digitorum insert?
Divides into the 4 tendons which is inserted into the middle and distal phalanges of the medial four fingers through the extensor expansion
What is the nerve supply of the extensor digitorum?
Posterior interosseous nerve
What is the action of the extensor digitorum?
1) Extension of all joints of the medial 4 fingers
2) Assists in extension of the wrist joint
What is the origin of the extensor digiti minimi
The common extensor origin (front of the lateral epicondyle of the humerus)
Where does the extensor digiti minimi insert?
Extensor expansion of the little finger
What is the nerve supply of the extensor digiti minimi?
Posterior interosseous nerve
What is the action of the extensor digiti minimi?
1) Extends all joints of the little finger
2) Assists in the extension of the wrist joint
What is the origin of the anconeus?
The back of the lateral epicondyle of the humerus
- All muscle arise from the front except anconeus
Where does the anconeus muscle insert?
1) Lateral side of the olecranon
2) Upper 1/4 of the posterior surface of the ulna
What is the nerve supply of the anconeus muscle?
Radial nerve
What is the action of the anconeus?
Assists the triceps in extension of the elbow joint
What are the muscles of the deep group of the posterior compartment?`
1) Supinator muscle
2) Abduct pollicis longus
3) Extensor pollicis longus
4) Extensor pollicis brevis
5) Extensor indicis
What is the origin of the supinator muscle?
1) Supinator crest and supinator fossa of the ulna
2) Lateral epicondyle of the humerus
3) Annular ligament
Where does the supinator muscle insert?
Front, lateral, and the back surface of the upper 1/3 of the radius
What nerve innervates the supinator muscle?
Posterior interosseous nerve
where is the anatomical snuff box located?
It is a depression of the lateral side of the wrist, identified when the thumb is abducted and extended
What is the action of the supinator muscle?
Supination of the forearm
- Supinator muscles are the supinator and brachioradialis (initiates supination)
- Muscles for pronation: Pronator teres, pronator quadratus, brachioradialis (initiation)
What are the boundaries of the snuff box?
1) Anteriorly:
- Tendon of abductor pollicis longus
- Tendon of extensor pollicis brevis
2) Posteriorly:
- Tendon of extensor pollicis longus
3) Floor:
- Radial artery
- Styloid process of the radius in its upper part
- Scaphoid bone in its lower part
What is the origin of the radial nerve?
Continuation of the posterior cord of the brachial plexus
Describe the course of the radial nerve
1) Descend behind the 3rd part of the axillary artery and the proximal part of the brachial artery lying in front of the subscapularis, teres major, and latissimus dorsi
2) Passes posterolaterally through the lower triangular space between the long and medial heads of the triceps
3) Runs with the profunda vessels in the spiral (radial) groove between the lateral and medial heads of the triceps
4) At the lateral border of the humerus it pierces the lateral intermuscular septum to enter the anterior compartment
5) Enters the forearm in front of the lateral epicondyle between the brachialis medially and the brachioradialis & ECRL laterally
6) Gives the posterior interosseous branch (deep radial) and continues as the superficial branch of the radial nerve
Describe the course of the superficial radial nerve (a branch of the radial nerve)
Descends on the lateral side of the front of the upper 2/3 of the forearm under cover of the brachioradialis
Describe the course of the posterior interosseous nerve
1) Pierces the supinator (pass between the 2 planes of its fibers) to appear on the back of the forearm
2) Winds backward around the lateral side of the radius, Descends between the superficial and deep muscles of the back of the forearm with the posterior interosseous artery, Ends deep to the extensor retinaculum
What are the branches of the radial nerve?
A) In the arm:
1) Muscular (Triceps and back of the forearm)
2) Cutaneous (lower lateral cutaneous nerve of the arm and posterior cutaneous nerve of the forearm
3) Articular
What are the branches of the superficial radial nerve?
It does not give any branches only cutaneous in the back of the hand
What are the branches of the posterior interosseous nerve?
A) Before piercing the supinator muscle:
1) Muscular to
- Extensor carpi radialis brevis
- Supinator muscle
B) After piercing the supinator muscle
- Extensor digitorum.
- Extensor digiti minimi.
- Extensor carpi ulnaris.
- Abductor pollicis longus.
- Extensor pollicis brevis.
- Extensor pollicis longus.
- Extensor indicis
C) Articular branches from its termination to:
- Inferior radioulnar
-Wrist
- Intercarpal joints
What happens if the radial nerve is injured after giving the posterior interosseous branch?
Sensory problems
What is the extensor retinaculum?
Strong fibrous band that extends obliquely across the back of the wrist
- Holds the tendon that goes to the dorsum of the hand
What does the extensor retinaculum fiber attach to?
1) Medially
- Triquetral
- Pisiform
- Styloid process of ulna
2) Laterally
- Anterior border of radius
What are the structures that pass superficial to the extensor retinaculum?
1) Dorsal cutaneous branch of the ulnar nerve (medially)
2) Basilic vein (medially)
3) Cephalic vein (laterally)
4) Superficial branch of the radial nerve (laterally)
What are the structures that pass deep to the extensor retinaculum?
- Divided into 6 compartments
1) Abductor pollicis longus and extensor pollicis brevis
2) Extensor carpi radialis longus & Extensor carpi radialis brevis
3) Extensor pollicis longus
4) Extensor digitorum, extensor indicis, anterior interosseous artery and posterior interosseous nerve
5) Extensor digiti minimi
6) Extensor carpi ulnaris
