Elbow and forearm: Bones and muscles

Question 1

What are the bones of the forearm?

Answer 1

Humerus
Radius (Lateral)
Ulna (Medial)

Question 2

What are the regions of the forearm?

Answer 2

Cubital fossa
Anterior compartment - flexor
Posterior compartment - Extensor

Question 3

What structures are on the anterior surface of the humerus?

Answer 3

Lesser tubercle
Intertubercular groove
Coronoid fossa
Radial Fossa
Capitulum

Trochlea, head and surgical neck, deltoid tuberosity and lateral/medial epicondyles on anterior and posterior

Question 4

What structures are on the posterior surface of the humerus?

Answer 4

Greater tubercle
Anatomical neck
Nutrient foramen
Olecranon fossa

Question 5

What are the main components of the radius?

Answer 5

Head of radius
Neck of radius
Tuberosity of radius
Styloid process
Ulnar notch of radius
Articular facets
Interosseous margin

Question 6

What are the main components of the ulna?

Answer 6

Olecranon
Trochlear notch
Radial notch of ulna
Coronoid process
Tuberosity of ulna
Interosseous margin
Head of ulna

Question 7

What is a ‘Colles’ fracture of radius?

Answer 7

Distal radius (with clavicle) most commonly fractured upper limb bone (Colles) especially in elderly.

Question 8

How can the ulna be dislocated and fractured?

Answer 8

Posterior dislocation: Prominence of olecranon posteriorly and distal humerus anteriorly

Fracture of coronoid process with posterior elbow dislocation. Coronoid fracture may occur without dislocation

Question 9

Fascial compartments

Answer 9

Fascia of arm: Brachial fascia
Fascia of forearm: Antebrachial fascia

Act to tightly bind down muscles
Significant rise in pressure (e.g. - from bleeding or oedema) can lead to compression of contents - compartment syndrome

Question 10

What is the cubital fossa?

Answer 10

It is the area between medial and lateral epicondyles, pronator teres and brachioradialis.
Its roof is the bicipital aponeurosis
Its floor is the brachialis muscle

It contains:

• Medial cubital vein
• Cutaneous nerves
• Ulnar and radial arteries
• Medial and radial nerves

Question 11

Muscles of the forearm (general)

Answer 11

Flexors more powerful than extensors
Skin overlying flexor muscles more sensitive than that over extensors
Supplied by 3 nerves - median, ulnar and radial

Question 12

How is the anterior flexor compartment of the forearm organised?

Answer 12

It is organised into 3 layers

• Superficial
• Intermediate
• Deep

Question 13

What muscles are located in the superficial later of the AFC of the forearm? Where do they originate?

Answer 13

The muscles all originate from the common flexor origin - medial epicondyle.

1. Pronator teres (PT)
2. Flexor Carpi radialis (FCR) - Flexes wrist on the radial side
3. Palmaris longus (PL)
4. Flexor carpi ulnaris (FCU) - Flexes wrist on the ulnar side

Question 14

What muscle is located in the intermediate layer of the AFC of the forearm? Where does it originate?

Answer 14

Flexor digitorum superficialis (FDS)
It arrises from the common flexor origin, radius and ulna.
It flexes the had at the carco-metacarpal joints
It flexes fingers at first metacarpal joint

Question 15

What muscles are located in the deep layer of the AFC of the forearm? Where do they originate?

Answer 15

They originate from the radius and ulna, with and without I/O membrane.

1. Flexor pollicis longus (FPL) - Flex at interphalangeal joints
2. Flexor Digitorum Profundus (FDP) - Insert into medial and distal phalanges
3. Pronator Quadratus (PQ) - From radius to ulna; pronator

Question 16

What are the pronators and supinators?

Answer 16

Pronators: Pronator teres and pronator quadratus - together they pronate the forearm. If there is inflammation, they will pinch the median nerve

Supinator: Supination is the more powerful action; action also produced by biceps. Radius moves relative to ulna.

Question 17

Median nerve

Answer 17

• Comes from medial and lateral cords (C5-T1)
• Supplies all but 1.5 muscles of anterior compartment of forearm: PT, FCR, PL, FDS, FPL, PQ, FDP (lateral two tendons)
• Passes via pronator teres to forearm and carpal tunnel to hand
• Anterior interosseous nerve
• Compression at the elbow: Functional deficit, hand of benediction

Question 18

Ulnar nerve

Answer 18

• Comes from medial cord (C8, T1)
• Supplies 1.5 muscles in anterior compartment: FCU and FDP (medial two tendons)
• Susceptible to compression and/or stretch across back of medial epicondyle - functional deficits, claw hand

Question 19

How is the posterior extensor compartment of the forearm organised?

Answer 19

It is organised into two layers:

• Superficial
• Deep

Question 20

What muscles are located in the superficial layer of the PEC of the forearm? Where do they originate?

Answer 20

Most arise from the common flexor origin - lateral epicondyle

1. Bracioradialis
2. Extensor carpi radialis longus (ECRL)
3. Extensor carpi radialis brevis (ECRB)
4. Extensor digitorum communis (EDC)
5. Extensor digiti minimi (EDM)
6. Extensor carpi ulnaris (ECU)
7. Anconeus

Question 21

What muscles are located in the deep layer of the PEC of the forearm? Where do they originate?

Answer 21

Most arise from the ulna with/without radius and interosseous membrane.

1. Supinator
2. Abductor pollicis longus (APL)
3. Extensor pollicis brevis (EPB)
4. Extensor pollicis longus (EPB)
5. Extensor indicis (EI)

Question 22

Radial nerve

Answer 22

• Comes from posterior cord (C5-T1)
• Supplies muscles of arm and forearm
• Runs across shaft of humerus between med/lat heads of triceps
• Superficial and deep branches
• Posterior interosseous nerve
• Susceptible to damage in humeral shaft fracture, compression - saturday night palsy
• Supplies skin of arm, forearm and back of hand.