L3.3 Antebrachial Compartment

Question 1

Ulna

Answer 1

• Proximal wide
  
  • Has semi-lunar notch→ Olecranon (Top) & Coranoid (bottom)
• Distal narrow (head)
• Lateral radial notch (for head of radius)
• Tuberosity → brachialis muscle
• Styloid process at head

Question 2

Radius

Answer 2

• Proximal around head (sits in radial notch)
• Neck of radius (constriction ~ head)
• Tuberosity → biceps
• Distal projection → also styloid process

Question 3

What is the joint between the radius and ulna?

And what is the orientation and function of the interosseous membrane?

Answer 3

Obliquely oriented → stress shared between bones

Question 4

Common fracture of the radius?

Answer 4

• Distal end → “Colles” fracture
• Force also transferred to ulnar

Question 5

Common fracture of the ulna?

Answer 5

• From falling on elbow
• Olecanon breaks → dislocates elbow joint
  
  • Inhibits ulnar nerve & brachial artery → Volksman ischaemia

Question 6

What is the function of the antebrachial fascia?

What is the order of the structures first affected oedema/built up of pressure in the fascia?

Answer 6

• bind muscles tightly → allows muscles to work better
• Separates flexors & extensors
• Deep to wrist → fascia becomes thicker → retinaculum
• Oedema/built up of pressure in fascia → compartment syndrome
  
  • Order of structures first affected:
    
    • 1) Veins & lymphatics
    • 2) Superficial Nerves
    • 3) Arteries
    • 4) Deep Nerves

Question 7

What are the borders of the cubital fossa?

And what are the structures running through the cubital fossa?

Answer 7

• Btw med & Lat epicondyles, pronator teres & brachioradialis
• Roof: Bicipital aponeurosis
• Floor → Brachialis
• Structures through cubital fossa (from LAT to MED):
  
  • Radial N
  • Biceps brachii tendon
  • Brachial A
  • Median N
  • *SUP veins (median cubital vein) - but usually SUP to fossa*

Question 8

ANT Superficial Antebrachial muscles (4)

Answer 8

*ANT more powerful than POS muscles, overlying skin also more sensitive*

• SUPERFICIAL (P,F,P,F) – All originate from CFO
• Pronator teres (PT)
  
  • Origin: CFO; Insertion: Lat radius
  • 2 heads → median N travels in between
  • Does not cross wrist, pronation may compress median N
• Flexor carpi radialis (FCR)
  
  • Origin: CFO; Insertion: base of 2nd & 3rd metacarpal bones
  • 2 heads
• Palmeris Longus (PL)
  
  • Origin: CFO; Insertion: Palmar aponeurosis
  • Not important: absent in 50% population
  • But on top of Median N → gives protection
• Flexor carpi ulnaris (FCU)
  
  • Origin: CFO; Insertion: 5th metacarpal
  • Innervated entirely by ulnar N

Question 9

ANT Intermediate Forearm muscles (1)

Answer 9

Flexor digitorum superficialis (FDS)

• Origin: CFO; Insertion: 4 digits (not thumb) → spits into 2 branches → then inserts into middle base of phalanges
• Flexes proximal phalanges

Question 10

ANT Deep Forearm muscles (3)

Answer 10

• Flexor pollicis longus (lat) (FPL):
  
  • Origin: Shaft of radius & Interosseous membrane; Insertion: base of phalangeal thumb
  • Flexion of phalangeal thumb
• Flexor digitorum profunda (FDP):
  
  • Origin: Shaft of ulnar & Interosseous membrane; Insertion: base of distal phalanges (through the split space of FDS → lat phalanges)
  • Through carpal tunnel
  • Flexes hand & interphalangeal joints
• Pronator quadratus (PQ):
  
  • Origin: Ulnar; Insertion: Radius
  • Does not cross wrist
  • Pronator of forearm

Question 11

POS Superficial Forearm (6)

Answer 11

• Brachioradialis (WEIRD ONE)
  
  • Origin: Lat supracondylar ridge of humerus; Insertion: Radial styloid process
  • Innervated by radial N (POS) BUT, functionally ANT
  • Flexes wrist
• Extensor carpi radialis longus
  
  • Origin: Lat supracondylar ridge of humerus; Insertion: 2nd MC
• Extensor carpi radialis brevis
  
  • Origin: CEO; Insertion: 3rd MC
• Extensor digitorum communis
  
  • Origin: CEO; Insertion: Extensor expansion of 4 digits (not thumb)
• Extensor digiti minimi
  
  • Origin: CEO; Insertion: Extensor expansion of 5th finger
• Extensor carpi ulnaris
  
  • Origin: CEO; Insertion: 5th MC
  • If flexor & extensor works tgt → causes ulna deviation

Question 12

POS deep Forearm (5)

Answer 12

• Supinator
  
  • Origin: CEO & Ulna; Insertion: Proximal Radial shaft
  • Radial N pierces it & splits into 2 divisions
    
    • Superficial: Innervates brachioradialis
    • Deep: Innervates POS compartment → goes through anatomical snuff box
• Abductor pollicis longus
  
  • Origin: Ulna, radius, interosseous membrane; Insertion: Thumb
  • Crosses ECRL & B
• Extensor pollicis brevis
  
  • Origin: Radius, interosseous membrane; Insertion: Thumb
• Extensor pollicis longus
  
  • Origin: Ulna, interosseous membrane; Insertion: Thumb
• Extensor indicis (EI)
  
  • Origin: Ulna, interosseous membrane; Insertion: Index finger