Posterior Forearm Muscles

Question 1

Superficial compartment 
Extensor digitorum 
- Origin and insertion?
- Actions?
- Innervation?

Answer 1

• Origin: lateral epicondyle of humerus
• Insertion: extensor expansion of each finger (middle and distal phalanges)
• Action: extension of fingers at MCPJ and IPJs
• Innervation: deep branch of radial nerve

Question 2

Superficial compartment
Brachioradialis 
- Origin and insertion?
- Actions?
- Innervation?

Answer 2

• Origin: lateral mid-shaft humerus (supracondylar ridge)
• Insertion: distal radius
• Action: flexion of elbow
• Innervation: radial nerve

Question 3

Superficial compartment
Extensor carpi radialis brevis and longus
- Origin and insertion?
- Actions?
- Innervation?

Answer 3

• Origin: ECRB lateral epicondylitis, ECRL supracondylar ridge of humerus
• Insertion: metacarpals 2 & 3
• Action: extension and abduction of wrist
• Innervation: radial nerve

Question 4

Superficial compartment 
Extensor digiti minimi
- Origin and insertion?
- Actions?
- Innervation?

Answer 4

• Origin: lateral epicondyle
• Insertion: joins with extensor digitorum inserting into extensor expansion of little finger
• Action: extension of little finger
• Innervation: deep branch of radial nerve

Question 5

Superficial compartment Extensor carpi ulnaris

• Origin and insertion?
• Actions?
• Innervation?

Answer 5

• Origin: lateral epicondyle
• Insertion: base of metacarpal 5
• Action: extension and adduction of wrist
• Innervation: deep branch of radial nerve

Question 6

Superficial compartment
Anconeus 
- Origin and insertion?
- Actions?
- Innervation?

Answer 6

• Origin: lateral epicondyle
• Insertion: postero-lateral olecranon
• Actions: extends and stabilises the elbow joint, abducts ulna during pronation
• Innervation: radial nerve

Question 7

Deep compartment 
Supinator 
- Origin and insertion?
- Actions?
- Innervation?

Answer 7

• Origin: 2 heads; one from lateral epicondyle of humerus, one from posterior ulna
• Insertion: posterior surface of radius
• Actions: supinate forearm
• Innervation: deep branch of radial nerve

Question 8

Deep compartment 
Extensor pollicis brevis
- Origin and insertion?
- Actions?
- Innervation?

Answer 8

• Origin: posterior surface of radius and interosseus membrane
• Insertion: proximal phalanx of thumb
• Action: extension of thumb at MCPJ and carpometacarpal joint (between 1st metacarpal and trapezius)
• Innervation: radial nerve (posterior interosseus branch)

Question 9

Deep compartment
Extensor pollicis longus
- Origin and insertion?
- Actions?
- Innervation?

Answer 9

• Origin: posterior surface of ulna and interosseus membrane
• Insertion: distal phalanx of thumb
• Actions: extension of carpometacarpal joint, MCPJ and IPJ of thumb
• Innervation: radial nerve (posterior interosseus branch)

Question 10

Deep compartment 
Abductor pollicis longus
- Origin and insertion?
- Actions?
- Innervation?

Answer 10

• Origin: interosseus membrane and posterior surfaces of radius and ulna
• Insertion: 1st metacarpal
• Action: abduction of thumb
• Innervation: radial nerve (posterior interosseus branch)

Question 11

Deep compartment 
Extensor indicis proprius
- Origin and insertion?
- Actions?
- Innervation?

Answer 11

• Origin: posterior surface of ulna and interosseus membrane
• Insertion: joins with extensor digitorum and inserts onto extensor expansion of index finger
• Action: extension of index finger -allows it to move independently of other fingers
• Innervation: radial nerve (posterior interosseus branch)