Forearm

Question 1

Muscles in the posterior compartment of the forearm perform which movement?
How does this differ to muscles in the anterior compartment?

Answer 1

Posterior compartment contains extensor muscles
They produce extension at the wrist and fingers

Anterior compartment contains flexor muscles

Question 2

Brachioradialis flexes the elbow. At which forearm position is it most effective?

Answer 2

Neutral position

Imagine a soldiers arms as he marches

Question 3

What is the function of brachioradialis?

In which forearm position does it merely assist in this function?

Answer 3

Brachioradialis flexes the elbow

In the supinated position (soup, please) brachioradialis only assists flexion. It is less effective than in the neutral position.

Question 4

Brachioradialis:
Origin?
Insertion?

Answer 4

Origin- proximal aspect of the lateral supracondylar ridge of the humerus
Insertion- next to the radial styloid process (distal)

Question 5

How many muscles are in the superficial compartment of the posterior forearm?
Name them.

Answer 5

7

(Lateral)
Brachioradialis 
Extensor carpi radialus longus 
Extensor carpi radialis brevis 
Extensor digitorum digitorum 
Extensor digiti minimi 
Extensor carpi ulnaris 
Anconeus

Question 6

Extensor carpi radialus longus 
Extensor carpi radialis brevis 
Extensor carpi ulnaris 
Which muscles are these?
What is their common origin?
What does carpi mean?

Answer 6

All superficial muscles of the posterior compartment

Insert onto the metacarpals of the hand
metacarpals link the carpals (wrist bones) to the phalanges (finger bones)

Carpi means wrist

Question 7

All muscles of the posterior compartment are innervated by which nerve?

Answer 7

Radial nerve

Question 8

What is the common extensor origin? (for some superfical muscles)

Answer 8

Lateral epicondyle

Question 9

Which of the 7 superfical extensor muscles do not originate at the lateral epicondyle?

Answer 9

Lateral epicondyle = common extensor origin

Brachioradialis, extensor carpi radialis longus and anconeus do not originate here

Question 10

Extensor carpi radialis longus shares the same origin as which other superficial posterior muscle?
What is the origin?

Answer 10

Brachioradialis

Both originate from the lateral side of the supracondylar ridge of the humerus

Question 11

Which other movement at the wrist do extensor carpi radialis longus (ECRL) and brevis (ECRB) perform?
How are they able to do this?

Answer 11

Abduction

Due to position on the radial side of the forearm

Question 12

Where do ECRL and ECRB insert?

How does their innervation differ?

Answer 12

Longus- dorsal (posterior) surface of the base of the 2nd metatarsal bone
(thumb is 1st)
Brevis- dorsal (posterior) surface of the base of the 3rd metatarsal bone

Both innervated by the radial nerve
ECRB innervated by the deep branch of the radial nerve (nerve branches into superficial and deep).

Question 13

There are 2 ‘extensor digitorum…’ muscles in the body.

What are their full names and different locations?

Answer 13

Extensor digitorum longus = foot

Extensor digitorum (communis) = superficial compartment of the posterior forearm

Question 14

What and where is the radial groove?

Answer 14

Shallow depression for the radial nerve and deep brachial artery
In the center of the lateral border of the humerus

Question 15

The radial nerve emerges from the radial groove on which side of the arm?
It emerges 5cm beneath which tuberosity?

Answer 15

Lateral side (radial)

The deltoid tuberosity (where deltoid muscle inserts)

Question 16

Describe the anatomical course of the radial nerve, beginning at the radial groove

Answer 16

• Radial nerve emerges from the radial groove on the lateral side of the arm.
• Gives off muscular branches to the brachioradialis and extensor carpi radialis longus
  (plus a small supply to the brachialis)
• Pierces the lateral intermuscular septum to enter the anterior compartment
• Travels through the cubital fossa anterior to the lateral epicondyle of the humerus
• Divides within the cubital fossa to give the superficial and deep branches
• Superfical branch (sensory) innervates dorsal surface of the lateral 3.5 digits (begin at thumb)
• Deep branch innervates extensor carpi radialis brevis and supinator muscles
• Deep branch exits cubital fossa posteriorly between 2 heads of the supinator and enters the posterior compartment of the forearm. Now called the posterior interosseous nerve
• Innervates all remaining muscles of the posterior forearm (superficial and deep).

Question 17

When does the radial nerve become the posterior interosseous nerve?

Answer 17

When it enters the posterior compartment of the forearm (after passing between the 2 heads of the supinator)

Question 18

Where does the extensor digitorum originate and insert?

Answer 18

Common extensor origin (lateral epicondyle of humerus)

Splits into 4 tendons and inserts into the extensor hoods of the 4 fingers

Question 19

Why can’t you fully extend the middle finger if your other fingers are flexed?
(finger flexion points downwards/ fist)

Answer 19

The 4 tendons of digitorum longus are linked (on the dorsal surface) by juncturae tendinum (fibrous bands).
Thus the finger is tethered to its flexed counterparts.

Question 20

How many muscles are in the superficial posterior compartment of the forearm?

The posterior interosseus nerve innervates which muscles of the superficial posterior compartment?

How are the other muscles innervated?

Answer 20

7 superficial muscles

The medial 3:
Extensor digitorum
Extensor digiti minimi
Extensor ulnaris

• Radial nerve innervates brachoradialis and extensor carpus radialis longus.
• Deep radial nerve innervates extensor carpi radialis brevis.

Question 21

Role of the extensor digitorum muscle?

Answer 21

Main extensor of the fingers

Extends at the metacarpophalangeal and interphalangeal joints

Question 22

Where does extensor digiti minimi insert?

What is its role?

Answer 22

Inserts into the extensor hood of the little finger (ulnar/ medial side)
Extends the little finger and assists in wrist extension

Question 23

Which superficial posterior muscle has 2 heads?

Where do they originate and insert?

Answer 23

Extensor carpi ulnaris

• Humeral head originates at common extensor origin (lateral epicondyle of humerus)
• Ulnar head originates at the olecranon process of the ulnar
• Both insert at the base of the fifth metacarpal

Question 24

Function of extensor carpi ulnaris?

Answer 24

Extends the wrist

Adducts the wrist (due to position on the ulnar side)

Question 25

Some extensor muscles can assist in movements other than extension.
Which muscles and why?

Answer 25

ECRL and ECRB - abduction due to radial position

Extensor carpi ulnaris - adduction due to ulnar position

Question 26

Anconeus originates from the humerus and inserts on the ulnar. What are the exact positions?

Which joint does it cross?

Answer 26

Common extensor origin on humerus (lateral epicondyle)
Inserts onto the radial side of olecranon process and posterior surface of ulnar

Elbow joint

Question 27

Role of the anconeus muscle?

Answer 27

• Assists triceps in elbow extension (very weak extensor alone)
• Stabilises the elbow joint
• Prevents impingement of the joint capsule during pronation (it abducts the ulna)

Question 28

In the posterior forearm, how many muscles are in the;

• Superficial compartment?
• Deep compartment?

Answer 28

7 superficial

5 deep

Question 29

Which of the 5 deep muscles in the posterior forearm are NOT innervated by the posterior interosseous nerve?
What is the innervation instead?

Answer 29

The supinator muscle is innervated by the deep radial nerve

It becomes the posterior interosseous nerve after passing between the 2 heads of the supinator

Question 30

Which nerve innervates 4/5 deep muscles of the posterior compartment?

Answer 30

Posterior interosseous nerve

The exception- deep radial nerve innervates the supinator muscle

Question 31

Where does the supinator muscle originate and insert?

Answer 31

It has 2 heads, the origins are:
Humeral head- common extensor origin (lateral epicondyle)
Ulnar head- Supinator crest (radial border of the proximal shaft)

Both insert together onto the proximal radial border of the radius. (No further than pronator teres insertion point on the ulnar)

Question 32

Role of the supinator?
Describe how its contraction carries out this role.
When does another muscle take the role over?

Answer 32

Supinate the forearm

Muscle contracts
- radial head rotates externally (laterally) in the annular ligament
(annular ligament encircles radius to keep it within the radial notch)
- radius rotates laterally over the ulna at the distal radioulnar joint

Biceps brachii supinates the arm under resistance

Question 33

Which tendons make up the radial and ulnar borders of the anatomical snuff box?

Answer 33

Radial border- abductor pollicis longus and extensor pollicis brevis
Ulnar border- extensor pollicis longus

Question 34

Name the 5 deep muscles of the posterior forearm

Answer 34

Supinator 
Abductor pollicis longus 
Extensor pollicis brevis 
Extensor pollicis longus 
Extensor Indicis

Question 35

Which structure separates the forearm into anterior and posterior compartments?

Answer 35

The interosseous membrane

sheet of fibrous tissue between the radius and ulna

Question 36

Abductor pollicis longus; origin and insertion?

Position relative to the supinator muscle?

Answer 36

Origin- interosseous membrane and adjacent posterior surfaces of the ulna and radius
Insertion- base of the 1st metacarpal (thumb) on the radial side

immediately distal to the supinator (all radial side)

Question 37

Extensor pollicis longus;
Origin and Insertion?
Role?

Answer 37

Origin- interosseous membrane and the lower third (‘middle third’) of the posterior ulnar
Inserts- distal phalanx of the thumb

Extends all joints of the thumb; carpometacarpal, metacarpophalangeal and interphalangeal

Question 38

Role of the extensor pollicis longus muscle?

How does it increase the force exerted?

Answer 38

Extends all joints of the thumb
Uses the dorsal tubercle of the wrist as a pulley to increase the force exerted
(On the ulnar side of the tubercle)

Question 39

Role of abductor pollicis longus?

Answer 39

• Radially abducts the thumb

- Assists in extension of the carpometacarpal joint (because it crosses the joint)