PNS 3 - Median Nerve

Question 1

What muscles are innervated by the axillary nerve?

Answer 1

Deltoid and Teres Minor. (Possibly also the long head of triceps brachii.)

Question 2

What motor functions are provided by the axillary nerve?

Answer 2

Abduction of the arm at the shoulder beyond the first 15°.

Question 3

What is the sensory distribution of the axillary nerve?

Answer 3

Skin over the superolateral shoulder, especially over the deltoid.

Question 4

Through which space does the axillary nerve exit the axilla?

Answer 4

The Quadrilateral (Quadrangular) Space.

Question 5

What are the boundaries of the Quadrilateral Space?

Answer 5

• Superior: Teres minor and subscapularis
• Inferior: Teres major
• Lateral: Surgical neck of the humerus
• Medial: Long head of triceps brachii

Question 7

What are the causes of axillary nerve injury?

Answer 7

• Proximal humeral fractures
• Anterior shoulder dislocation (traction/compression)
• Fibrous bands (post-traumatic)
• Soft tissue or osseous tumors
• Deep intramuscular injection
• Compression (e.g., sleeping prone with arms overhead)
• Penetrating injury
• Rotator cuff surgery
• Teres Syndrome (Quadrilateral Space Syndrome)

Question 8

What are the clinical signs of axillary nerve injury?

Answer 8

• Deltoid weakness (15–90° abduction)
• Deltoid atrophy (flat shoulder deformity)
• Sensory deficit or pain over superolateral shoulder
• Tenderness in quadrilateral space or teres minor insertion

Question 9

What muscles are innervated by the musculocutaneous nerve?

Answer 9

Biceps Brachii, Brachialis, Coracobrachialis (BBC).

Question 10

What motor functions are provided by the musculocutaneous nerve?

Answer 10

Flexion of the arm at the elbow and supination of the forearm.

Question 11

What is the sensory distribution of the musculocutaneous nerve?

Answer 11

Lateral surface of the forearm via the lateral antebrachial cutaneous

Question 12

Through which muscle does the musculocutaneous nerve travel?

Answer 12

The Coracobrachialis muscle.

Question 13

What are the causes of musculocutaneous nerve injury?

Answer 13

• Rare overall
• Most commonly affected upper limb nerve in diabetic neuropathy
• Direct trauma (e.g., humeral fracture, gunshot)
• Shoulder dislocation
• Rapid forearm extension
• Entrapment in coracobrachialis

Question 14

What are the clinical signs of musculocutaneous nerve injury?

Answer 14

• Weakness in elbow flexion and forearm supination
• Loss of biceps deep tendon reflex
• Sensory deficits and/or pain over the lateral forearm

Question 15

What muscles are innervated by the median nerve?

Answer 15

• Pronator Teres
• Palmaris Longus
• Flexor Carpi Radialis
• Flexor Digitorum Superficialis
• Flexor Digitorum Profundus (radial half)
• Flexor Pollicis Longus
• Pronator Quadratus
• Thenar muscles: Abductor Pollicis Brevis, Opponens Pollicis, Flexor Pollicis Brevis (superficial head)
• Lumbricals 1 and 2

Question 16

What are the motor functions of the median nerve?

Answer 16

• Thumb flexion and opposition
• Flexion of digits 2 and 3
• Wrist flexion and abduction
• Forearm pronation

Question 17

What is the sensory distribution of the median nerve?

Answer 17

• Isolated supply: Anterior and posterior distal tips of digits 2 and 3
• Primary zone – Anterior: Lateral 2/3 of hand (excluding distal tips of 2 and 3)
• Primary zone – Posterior: Distal 2/3 of fingers 2 and 3 and lateral half of finger 4 (excluding tips)

Question 18

What autonomic and proprioceptive roles does the median nerve have?

Answer 18

• Carries majority of autonomic fibers for arm, forearm, and hand
• Responsible for proprioception of all thumb movements and flexor surfaces of digits 2 and 3, and lateral wrist

Question 19

What nickname is given to the median nerve and why?

Answer 19

The “Tool Utilization” nerve – crucial for precision grip and fine motor control.

Question 20

What are common injury sites of the median nerve?

Answer 20

• Shoulder: Dislocations, trauma, some fractures
• Arm: Distal humeral fracture
• Elbow: Dislocations, medial epicondyle fracture, entrapment during reduction
• Forearm: Fractures, blows, lacerations, entrapment under FDS (Pronator Teres Syndrome)
• Wrist: Carpal tunnel, suicide attempts, fractures/dislocations

Question 21

What causes Pronator Teres Syndrome?

Answer 21

Entrapment between superficial and deep heads of pronator teres due to trauma, repetitive elbow motion (flexion, supination, pronation)

Question 22

What are the symptoms of Pronator Teres Syndrome?

Answer 22

Chronic forearm pain/aching with pronation, and paraesthesias in median nerve distribution.

Question 23

What is Anterior Interosseous Nerve Syndrome and how is it different?

Answer 23

• Caused by compression of the AIN (a motor branch of median nerve)
• No sensory loss, only motor impairment
• Differentiates from pronator teres or carpal tunnel syndrome

Question 24

What are the anatomical boundaries of the carpal tunnel?

Answer 24

• Lateral: Scaphoid and Trapezium tubercles
• Medial: Pisiform and hook of hamate
• Dorsal: Carpal bones
• Volarly: Flexor retinaculum (transverse carpal ligament)

Question 25

What are causes of carpal tunnel syndrome?

Answer 25

• Swelling from trauma/pregnancy • RA, OA • Wrist fractures • Repetitive motion/sustained awkward postures

Question 26

What muscles are involved in the median nerve’s motor functions (by area)?

Answer 26

• Forearm Pronation: Sole – Pronator Teres, Pronator Quadratus • Wrist Flexion: Shared – Flexor Carpi Radialis, FPL, FDS, FDP (radial ½) • Wrist Abduction: Shared with radial nerve – Flexor Carpi Radialis • Thumb Opposition: Sole – Opponens Pollicis • Thumb Flexion: Shared with ulnar – FPL, FPB (superficial head) • Thumb Abduction: Shared with radial – Abductor Pollicis Brevis • Finger Flexion: - Sole: Fingers 2 and 3 – FDP (lateral ½), FDS, Lumbricals 1 and 2 - Shared with ulnar: Fingers 4 and 5 – FDS

Question 27

What special tests are used to assess the median nerve?

Answer 27

• Rule out C-spine and Thoracic Outlet Syndrome • Neural tension test • Muscle testing: - Pronator Teres – flaccidity - FDS – weakness in DIP flexion (shared with ulnar) - Thumb Opposition – flaccidity - Abductor Pollicis Brevis – weakness in thumb abduction • Special Tests: Phalen’s, Reverse Phalen’s, Tinel’s at wrist, Pinch test ("OK" sign)

Question 28

Does vasomotor paralysis occur with proximal median nerve loss?

Answer 28

Yes. The median nerve carries the majority of autonomic fibers for the entire arm, forearm, and hand.

Question 29

What signs indicate vasomotor paralysis due to median nerve loss?

Answer 29

Massive edema, loss of hair, tissue fragility, dryness, trophic changes, and nail bed dysfunction. The skin may appear thin, shiny, and lacking lines.

Question 30

Where is vasomotor paralysis seen in median nerve injury?

Answer 30

Throughout the entire arm, forearm, and hand.

Question 31

What proprioceptive losses occur with complete median nerve injury?

Answer 31

Significant loss of proprioception to the thumb, flexor surfaces of fingers 2 & 3, and radial aspect of the wrist joint.

Question 32

What is an "Ape Hand Deformity," and what causes it?

Answer 32

"Ape Hand" refers to a deformity caused by full loss of median nerve function, where the thumb is adducted and unable to oppose.

Question 33

What happens when a patient with complete median nerve loss attempts to form a fist?

Answer 33

They display "Oath Hand," where only the ulnar-innervated fingers (4 & 5) flex, while digits 2 & 3 remain extended due to paralysis.

Question 34

Which muscles act as unopposed antagonists in median nerve injury?

Answer 34

Thumb adductors, extensors of digits 2 & 3, and supinators become unopposed due to the loss of their median-nerve-opposed muscles.