Muscles of the Upper limb (for nerds 🤓)

Peripheral nerves

Sensory innervation areas of the peripheral nerves (arm, ventral view)

Sensory innervation areas of the peripheral nerves (arm, dorsal view)

Axillary nerve (C5-C6)

Course

• It enters the arm through quadrangular space then courses around surgical neck of humerus.

Supply

• Motor
  • Deltoid muscles
  • Teres minor muscle
• Sensory
  • lateral cutaneous nerve of the arm→ Sensation of skin around deltoid and lateral arm.

Causes of injury

• Fractured surgical neck of humerus
• Anterior dislocation of humerus

Presentation

• Flattened deltoid
• Loss of arm abduction at shoulder (>15°)
• Loss of sensation over deltoid and lateral arm
• Teres minor affection

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Quadrangular space

• Borders
  • Cranial: teres minor muscle
  • Caudal: teres major muscle
  • Medial: triceps brachii (long head)
  • Lateral: humerus
• Structures within
  • Posterior humeral circumflex artery and vein
  • Axillary nerve
  • Visual mnemonic </aside>

                                    **Axillary nerve neuropathy**

Musculocutaneous nerve (C5-C7)

Course

• In the arm
  • It Pierces coracobrachialis muscle innervating it
  • It descends between brachialis and biceps brachii muscles innervating them.
  • It ends with lateral cutaneous nerve of the forearm around lateral epicondyle.

Supply

• Motor
  • Biceps brachii→ Flexion and supination
  • Brachialis and coracobrachialis muscles→ Flexion.
• Sensory
  • Lateral cutaneous nerve of the forearm → Sensation of the dorsal and radial forearm.

Causes of injury

• Upper trunk compression

Presentation

• Loss of forearm flexion and supination
• Loss of sensation over radial and dorsal forearm
• ↓ biceps (C5-C6) reflex

Median nerve (C5-T1)

Course

• In the arm

  • It accompanies brachial artery along the medial side of the arm.

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    Clinical note

    • Laceration of the cubital fossa can affect brachial artery and median nerve.
      • Explanatory picture </aside>

• In the forearm

  • It enters the forearm through the cubital fossa between 2 heads of pronator teres → the enter the anterior compartment of the forearm supplying all flexors of muscles except FCU and ulnar 1/2 of FDP.
    • Main median branch → passes between FDP and FDS supplying superficial flexors of the forearm.
    • Anterior interossei nerve → Once the main branch of the median nerve exits the two heads of the pronator teres, it gives rise to the anterior interosseous nerve, innervating the deep flexors of the forearm.

• In the wrist

  • It passes deep to flexor retinaculum (carpal tunnel)
  • Proximal to carpal tunnel it gives palmar branch of median nerve which passes superficial to flexor retinaculum which gives sensory innervation to lateral side of the palm.

• In the hand

  • It gives recurrent median nerve branch which gives motor innervation only to the thenar muscles of the hand.

Supply

• Motor
  • Forearm
    • All forearm flexors (except FCU & medial 1/2 FDP)
      • Median nerve itself → supply superficial group of forearm flexors
      • Anterior interosseous nerve → supply deep group of forearm flexors (eg, flexor digitorum profundus)
  • Hand
    • Lateral 2 lumbrical muscles
    • Thenar muscles (Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis) (LOAF)
• Sensory
  • Palmar branch of median nerve (only spared in CTS)→ , Lateral 2/3 of the palm (thenar eminence)
  • Common proper digital nerve→ Palmar surface of the Lateral 3 1/2 fingers.

Causes of injury

• Proximal lesion→ Supracondylar fracture of humerus
• Distal lesion→ Carpal tunnel syndrome and wrist laceration

Presentation

• "Ape hand" and "Hand of benediction,"
  • Loss of wrist flexion and function of the lateral two lumbricals, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (LOAF)
  • Loss of sensation over thenar eminence and dorsal and palmar aspects of lateral 3 1/2 fingers with proximal lesions.

                  **Ape hand**

               **Median nerve neuropathy**

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Ulnar nerve (C8-T1)

Radial nerve (C5-T1)