Muscles and movements of upper limb

Shoulder & Axilla - Movers & Shakers

• Rotator Cuff (SITS): Stabilizes glenohumeral joint.

  • Supraspinatus: Initiates abduction (first 15°); Suprascapular n.
  • Infraspinatus: External rotation; Suprascapular n.
  • Teres Minor: External rotation; Axillary n.
  • Subscapularis: Internal rotation; Subscapular n.
  • 📌 SITS muscles reinforce the joint capsule.

• Primary Movers:

  • Deltoid: Prime abductor (>15°); Axillary n.
  • Serratus Anterior: Protracts & rotates scapula (holds to thoracic wall); Long thoracic n.
  • Trapezius: Elevates, retracts, depresses scapula; Accessory n. (CN XI).

⭐ Winging of the Scapula: Injury to the Long Thoracic Nerve leads to paralysis of the Serratus Anterior muscle, causing the medial border of the scapula to protrude, especially when pushing against a wall.

Arm & Forearm - Flex & Extend

• Arm: Anterior Compartment (Flexion)

  • Muscles: Biceps brachii, Brachialis, Coracobrachialis.
    • 📌 Mnemonic: BBC
  • Innervation: Musculocutaneous nerve (C5-C7).
  • Action: Flexes elbow & shoulder; supinates forearm.

• Arm: Posterior Compartment (Extension)

  • Muscle: Triceps brachii.
  • Innervation: Radial nerve (C6-C8).
  • Action: Extends elbow.

• Forearm: Anterior Compartment (Flexion)

  • Action: Flexes wrist & digits.
  • Innervation: Primarily Median nerve.
    • Ulnar nerve supplies flexor carpi ulnaris & medial half of flexor digitorum profundus.

• Forearm: Posterior Compartment (Extension)

  • Action: Extends wrist & digits.
  • Innervation: Radial nerve.

⭐ Injury to the musculocutaneous nerve results in weak elbow flexion and supination, with sensory loss over the lateral forearm.

Intrinsic Hand Muscles - Fine-Tuning Grips

• Thenar Eminence (Median Nerve): Controls thumb opposition.
  • 📌 OAF: Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis.
• Hypothenar Eminence (Ulnar Nerve): Controls 5th digit.
  • 📌 OAF: Opponens digiti minimi, Abductor digiti minimi, Flexor digiti minimi.
• Interossei Muscles (Ulnar Nerve): For finger abduction/adduction.
  • 📌 PAD: Palmar ADduct.
  • 📌 DAB: Dorsal ABduct.
• Lumbricals: Flex metacarpophalangeal (MCP) joints and extend interphalangeal (IP) joints.

⭐ Ulnar Claw & Froment's Sign: Most intrinsic hand muscles are innervated by the ulnar nerve. A lesion results in a weak grip and a positive Froment's sign (patient flexes thumb IP joint to hold paper).

Clinical Correlates - When Nerves Fail

• Long Thoracic N. (C5-C7): Serratus anterior paralysis → "Winging of Scapula." Vulnerable during mastectomy.
• Axillary N. (C5-C6): Fracture of surgical neck of humerus. Deltoid paralysis (impaired arm abduction >15°), sensory loss over deltoid.
• Radial N. (C5-T1): Mid-shaft humerus fracture, crutch palsy → "Wrist Drop" (extensor failure).
• Median N. (C6-T1): Supracondylar fracture, carpal tunnel syndrome → "Ape Hand" (thenar atrophy), loss of thumb opposition. 📌 LOAF muscles affected.
• Ulnar N. (C8-T1): Medial epicondyle fracture ("funny bone") → "Ulnar Claw" at rest, hypothenar atrophy, weak adduction/abduction of fingers.

⭐ Exam Favourite: "Hand of Benediction" (Median N. injury) appears when trying to make a fist, while "Ulnar Claw" (Ulnar N. injury) is present at rest.

High‑Yield Points - ⚡ Biggest Takeaways

• Rotator cuff (SITS) muscles stabilize the shoulder; supraspinatus initiates abduction.
• Axillary nerve injury (surgical neck of humerus) paralyzes the deltoid, impairing abduction >15°.
• Long thoracic nerve palsy paralyzes the serratus anterior, causing a “winged scapula”.
• “Wrist drop” is the hallmark of radial nerve injury, affecting forearm extensors.
• Median nerve compression in the carpal tunnel causes thenar atrophy and sensory loss.
• Ulnar nerve damage results in a “claw hand” and sensory loss to medial digits.