2. Gross Anatomy of Upper Limb

Learning Objectives

• Identify the bones, joints, and ligaments of the shoulder girdle, arm, forearm, and hand
• Describe the origin, insertion, and action of the major muscles of the upper limb organized by compartment
• Trace the branches of the brachial plexus and predict motor and sensory deficits when specific nerves are injured
• Map the arterial supply from the subclavian artery through the palmar arches to the digits
• Explain the anatomical basis of common upper limb nerve injuries including radial, ulnar, median, and musculocutaneous nerve palsies
• Apply surface anatomy landmarks to guide clinical procedures such as venepuncture and joint aspiration
• Correlate brachial plexus root levels (C5-T1) with dermatomes and myotomes tested on clinical examination

Quick Answer

The upper limb is organized into four functional regions — the shoulder girdle, arm, forearm, and hand — connected by the brachial plexus (C5-T1) and the axillary-brachial arterial axis. The shoulder girdle (clavicle and scapula) anchors the limb to the thorax while allowing the greatest range of motion of any joint in the body. The humerus, radius, and ulna form the levers for elbow and forearm movements, while the intricate carpals, metacarpals, and phalanges enable fine motor precision. Clinically, nerve injuries follow predictable anatomical paths: radial nerve damage at the spiral groove causes wrist drop, ulnar nerve damage at the cubital tunnel causes claw hand, and median nerve compression at the carpal tunnel causes thenar wasting.

Overview

The upper limb consists of three main regions: the shoulder girdle, arm (humerus), and forearm. Each region contains various bones, joints, muscles, and other soft tissues that work together to enable movement, support, and sensory perception.

Key Components

• Bones: Provide structural support and protection
• Muscles: Enable movement through contraction and relaxation
• Joints: Allow for flexibility and range of motion
• Nerves: Control muscle function and transmit sensory information
• Blood Vessels: Supply oxygen and nutrients to tissues

Detailed Anatomy

Shoulder Girdle

The shoulder girdle or pectoral girdle consists of two clavicles (collarbones) and two scapulae (shoulder blades). It connects the upper limb to the trunk of the body. The glenohumeral joint is a ball-and-socket joint stabilized by the rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis — SITS).

Clavicle

• Shape: Long, narrow bone with an S-curve
• Function: Attaches scapula to sternum, transmits forces from the limb to the axial skeleton
• Key landmarks: Acromial end, sternal end; most commonly fractured bone in the body
• Clinical: Clavicle fractures typically occur at the junction of the middle and outer thirds

Scapula

• Shape: Triangular bone with a flat body and curved edges
• Function: Provides attachment points for 17 muscles
• Key landmarks: Spine of scapula, acromion process, coracoid process, glenoid fossa, superior and inferior angles

Arm (Humerus)

The humerus is the longest bone in the upper limb, extending from the shoulder joint to the elbow.

Humerus Structure

• Proximal end: Head (articulates with glenoid), greater and lesser tubercles (rotator cuff insertion)
• Shaft: Radial (spiral) groove houses the radial nerve and profunda brachii artery — fracture here = radial nerve palsy
• Distal end: Medial epicondyle, lateral epicondyle, trochlea (for ulna), capitellum (for radius), olecranon fossa

Key Muscles of the Arm

• Biceps brachii: Flexes elbow, supinates forearm; long head tendon passes through glenohumeral joint (prone to tendinopathy)
• Triceps brachii: Only extensor of the elbow; innervated by radial nerve — tests C7
• Brachialis: Primary elbow flexor, works regardless of forearm position
• Coracobrachialis: Assists in flexion and adduction of the arm

Brachial Plexus (C5-T1)

The brachial plexus is organized as Roots-Trunks-Divisions-Cords-Branches. Key branches include:

• Musculocutaneous nerve (C5-C7): Supplies biceps, brachialis, coracobrachialis; lateral cutaneous nerve of forearm
• Radial nerve (C5-T1): Posterior compartment of arm and forearm; wrist and finger extensors
• Median nerve (C6-T1): Anterior forearm flexors, thenar muscles, lateral two lumbricals; "hand of benediction" with proximal lesion
• Ulnar nerve (C8-T1): Hypothenar, interossei, medial two lumbricals; "claw hand" with distal lesion
• Axillary nerve (C5-C6): Deltoid and teres minor; tested by shoulder abduction

Erb's palsy (C5-C6): "Waiter's tip" — arm adducted, extended, forearm pronated; occurs with traction injury to upper trunk Klumpke's palsy (C8-T1): Claw hand with Horner syndrome; occurs with lower trunk injury

Forearm

The forearm contains two long bones: the radius and ulna, connected by the interosseous membrane.

Radius and Ulna

• Radius: Lateral bone (thumb side), rotates around ulna to produce pronation/supination; head articulates with capitellum
• Ulna: Medial bone (pinky side), primary articulation with trochlea; olecranon forms the elbow point

Anterior Compartment (Flexors — Median and Ulnar Nerve)

• Superficial: Pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris
• Deep: Flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, pronator quadratus

Posterior Compartment (Extensors — Radial Nerve)

• Superficial: Brachioradialis, extensor carpi radialis longus/brevis, extensor digitorum, extensor carpi ulnaris
• Deep: Supinator, abductor pollicis longus, extensor pollicis longus/brevis

Hand

The hand contains 27 bones: 8 carpals (arranged in two rows), 5 metacarpals, and 14 phalanges. The carpal tunnel transmits the median nerve and flexor tendons — compression causes carpal tunnel syndrome (thenar wasting, loss of opposition).

Intrinsic Muscles

• Thenar muscles (median nerve): Abductor pollicis brevis, flexor pollicis brevis, opponens pollicis
• Hypothenar muscles (ulnar nerve): Abductor digiti minimi, flexor digiti minimi, opponens digiti minimi
• Interossei and lumbricals: PAD = Palmar Adduct, DAB = Dorsal ABduct (both ulnar); lumbricals flex MCP, extend IP joints

Functions and Movements

1. Movement: Flexion, extension, abduction, adduction, rotation, and circumduction at shoulder, elbow, wrist, and finger joints
2. Sensory Perception: Receptors in skin and deeper tissues allow touch, pressure, temperature, and proprioception
3. Manipulation: Precision grip (median nerve) and power grip (ulnar nerve) are clinically distinct

Clinical Relevance

• Radial nerve palsy (wrist drop): Humeral shaft fracture, Saturday night palsy, crutch palsy
• Ulnar nerve palsy (claw hand): Cubital tunnel at elbow, Guyon's canal at wrist; ring and little finger affected
• Median nerve palsy (carpal tunnel syndrome): Most common entrapment neuropathy; thenar wasting, Tinel's and Phalen's signs positive; treated with corticosteroid injection or surgical release
• Rotator cuff tears: Supraspinatus most commonly torn (arm abduction 60-120 degrees painful); diagnosed with MRI
• Shoulder dislocation: Anterior dislocation (most common) — axillary nerve at risk; test deltoid and lateral arm sensation

Key Terms

Term	Definition	Related Concept
Brachial plexus	Network of nerves from C5-T1 supplying the upper limb	Erb's palsy, Klumpke's palsy
Rotator cuff	SITS muscles (supraspinatus, infraspinatus, teres minor, subscapularis) stabilizing glenohumeral joint	Shoulder impingement, rotator cuff tear
Carpal tunnel	Fibro-osseous channel at wrist transmitting median nerve and 9 flexor tendons	Carpal tunnel syndrome
Radial groove	Spiral groove on the posterior humerus carrying the radial nerve and profunda brachii artery	Humeral shaft fracture, wrist drop
Anatomical snuffbox	Depression between extensor pollicis longus and brevis tendons; floor = scaphoid	Scaphoid fracture
Thenar eminence	Muscle mass at base of thumb (abductor pollicis brevis, opponens pollicis, flexor pollicis brevis)	Median nerve palsy, carpal tunnel syndrome
Cubital tunnel	Passage posterior to medial epicondyle through which ulnar nerve travels	Ulnar nerve entrapment, claw hand
Interosseous membrane	Fibrous sheet connecting radius and ulna; transmits forces and separates compartments	Forearm fractures, compartment syndrome
Profunda brachii	Deep artery of the arm, accompanies radial nerve in the spiral groove	Radial nerve palsy
Median nerve	C6-T1 nerve supplying anterior forearm and thenar muscles; the "hand of benediction" nerve	Carpal tunnel syndrome, pronator teres syndrome

Common Mistakes

Misconception: Carpal tunnel syndrome is caused by ulnar nerve compression. Why it's wrong: The carpal tunnel specifically transmits the median nerve (and 9 flexor tendons). The ulnar nerve passes through a separate structure — Guyon's canal at the wrist. Correct understanding: Carpal tunnel syndrome (median nerve) presents with thenar wasting and loss of thumb opposition, while ulnar nerve compression at Guyon's canal presents with hypothenar wasting and claw posturing of the ring and little fingers.

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Misconception: Injury to the ulnar nerve at the elbow produces a worse claw deformity than injury at the wrist. Why it's wrong: This seems counterintuitive, but is called the "ulnar paradox." When the ulnar nerve is cut at the elbow, the flexor digitorum profundus to the ring and little fingers is also denervated, so those fingers cannot flex strongly — reducing the claw appearance. Correct understanding: A wrist-level ulnar nerve lesion spares the FDP (which is innervated more proximally) so the ring and little fingers flex maximally, producing a more pronounced claw. This is the ulnar paradox.

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Misconception: The deltoid muscle is tested by shoulder abduction from the start. Why it's wrong: The first 15 degrees of shoulder abduction is initiated by supraspinatus (C5-C6, suprascapular nerve), not deltoid. Correct understanding: Supraspinatus initiates abduction from 0-15 degrees; deltoid (axillary nerve, C5-C6) powers abduction from 15-90 degrees; trapezius and serratus anterior rotate the scapula to achieve full 180 degrees. Testing deltoid by resisting abduction above 15 degrees is appropriate in clinical practice.

Comparison and Connections

Feature	Radial Nerve Palsy	Ulnar Nerve Palsy	Median Nerve Palsy
Primary location of injury	Spiral groove of humerus (midshaft fracture)	Cubital tunnel (elbow) or Guyon's canal (wrist)	Carpal tunnel (wrist)
Motor deficit	Wrist drop, loss of finger and thumb extension	Intrinsic hand muscles (interossei, hypothenar); weak grip	Thenar muscles (opposition), lateral lumbricals
Sensory deficit	Dorsum of hand (especially first web space)	Little finger, medial half of ring finger	Lateral 3.5 fingers, thenar skin
Clinical sign	"Wrist drop" — cannot extend wrist against gravity	"Claw hand" — ring and little fingers clawed	"Pope's blessing" / "OK sign" weakness; thenar wasting
Reflex affected	Brachioradialis (C6), triceps (C7)	None routinely tested	None routinely tested
USMLE high-yield cause	Humeral shaft fracture, Saturday night palsy	Medial epicondyle fracture, leaning on elbow	Repetitive flexion, pregnancy, hypothyroidism

Practice Questions

Recall

1. Which muscles form the rotator cuff, and which nerve innervates each? Answer guidance: SITS — Supraspinatus (suprascapular nerve, C5-C6), Infraspinatus (suprascapular nerve, C5-C6), Teres minor (axillary nerve, C5-C6), Subscapularis (upper and lower subscapular nerves, C5-C6). Supraspinatus is most commonly torn.

2. Through which anatomical structure does the ulnar nerve pass at the wrist? Answer guidance: Guyon's canal (ulnar canal), medial to the carpal tunnel. The median nerve passes through the carpal tunnel. Distinguishing these two structures and their contents is frequently tested.

Understanding

3. Why does a mid-shaft humeral fracture cause radial nerve palsy but not necessarily affect elbow extension? Answer guidance: The radial nerve enters the spiral groove at the mid-humerus AFTER giving off the branch to the long head of triceps. The medial and lateral heads of triceps are also often spared. Therefore, elbow extension may be preserved despite complete radial palsy below the elbow, but wrist and finger extension will be lost.

4. Explain why division of the flexor retinaculum (carpal tunnel release) relieves carpal tunnel syndrome but does not impair wrist flexion. Answer guidance: The flexor retinaculum is the roof of the carpal tunnel. Cutting it decompresses the median nerve. Wrist flexion is powered by extrinsic flexor muscles whose tendons pass through the tunnel but whose muscle bellies are in the forearm — cutting the retinaculum does not impair those muscles.

Application

5. A 35-year-old construction worker presents with inability to extend his right wrist after sleeping in an awkward position with his arm over a park bench. Which nerve is affected, at what level, and what examination findings would you expect? Answer guidance: Radial nerve palsy at the spiral groove ("Saturday night palsy"). Expect wrist drop (cannot extend wrist against gravity), loss of finger and thumb extension, and decreased sensation over the dorsal first web space. Elbow extension is typically preserved (triceps branch exits proximal to groove). Brachioradialis reflex may be reduced.

6. A 55-year-old woman with poorly controlled hypothyroidism presents with bilateral hand numbness worse at night, relieved by shaking the hands. Which nerve is affected, and what provocative tests would confirm the diagnosis? Answer guidance: Median nerve compression in the carpal tunnel (carpal tunnel syndrome). Tinel's sign (tingling on percussion over the carpal tunnel) and Phalen's test (symptoms reproduced with wrist flexion for 60 seconds) confirm the diagnosis. Hypothyroidism, pregnancy, rheumatoid arthritis, and obesity are risk factors. EMG/nerve conduction studies confirm severity.

Analysis

7. Compare the expected clinical findings in a patient with an upper trunk brachial plexus injury (Erb's palsy) versus a lower trunk injury (Klumpke's palsy). Answer guidance: Erb's palsy (C5-C6): deltoid, biceps, supraspinatus, infraspinatus affected — arm hangs adducted, internally rotated, elbow extended, forearm pronated ("waiter's tip"). Sensation lost over lateral arm. Klumpke's palsy (C8-T1): intrinsic hand muscles affected — claw hand with hypothenar and interossei wasting. If T1 sympathetic fibers are involved, ipsilateral Horner syndrome (ptosis, miosis, anhidrosis) occurs.

8. A patient sustains an anterior shoulder dislocation. Which nerve is most at risk, and how would you test its integrity before and after reduction? Answer guidance: The axillary nerve (C5-C6) is most at risk because it winds posterior to the glenohumeral joint before supplying the deltoid and teres minor. Test by assessing sensation over the "regimental badge" area (lateral deltoid — the autonomous zone of the axillary nerve) and deltoid muscle power (shoulder abduction 15-90 degrees). Test before reduction to document pre-existing deficit and after to confirm resolution or identify new injury.

FAQ

Why is the clavicle the most commonly fractured bone in the body? The clavicle acts as a strut between the scapula and the sternum, transmitting forces from the upper limb to the axial skeleton. When a person falls on an outstretched hand (FOOSH) or receives a direct blow to the shoulder, the clavicle absorbs the transmitted force and fractures — most often at the junction of its middle and outer thirds, which is the thinnest and most curved segment. Pediatric clavicle fractures often heal with greenstick pattern, while adults may require surgical fixation with plate and screws if significantly displaced.

How do I remember which muscles are in each compartment of the forearm? Think of the forearm as having two main compartments: anterior (flexors, innervated by median and ulnar nerves) and posterior (extensors, innervated by radial nerve). A useful rule is that the median nerve innervates all anterior forearm muscles EXCEPT the flexor carpi ulnaris and the medial half of flexor digitorum profundus (both ulnar). In the posterior compartment, all muscles are radial nerve — remember the mnemonic BEST: Brachioradialis, Extensors, Supinator, Triceps (though triceps is in the arm, not forearm).

What is the clinical significance of the anatomical snuffbox? The anatomical snuffbox is the triangular depression visible on the dorsolateral wrist when the thumb is extended. It is bounded by the extensor pollicis longus medially and the extensor pollicis brevis/abductor pollicis longus laterally. The floor of the snuffbox is the scaphoid bone. Tenderness in the anatomical snuffbox after a FOOSH injury should be treated as a scaphoid fracture until proven otherwise — even if initial X-rays are negative (scaphoid fractures are frequently missed on plain films and require CT or MRI for confirmation). Scaphoid fractures can lead to avascular necrosis of the proximal pole if missed, because the blood supply enters distally.

What is the difference between a proximal and distal ulnar nerve lesion in terms of hand appearance? A proximal ulnar nerve lesion (at the elbow) paralyzes both the intrinsic hand muscles AND the flexor digitorum profundus to the ring and little fingers. Because the FDP is also out, the ring and little fingers cannot flex at the DIP joint — so the claw deformity is actually less pronounced. A distal lesion (at the wrist, such as in Guyon's canal) spares the FDP (innervated proximally), so the ring and little fingers can still flex strongly at the DIP — resulting in a more dramatic "claw." This counterintuitive finding is the "ulnar paradox."

How does knowledge of dermatomes help localize nerve root lesions in the upper limb? Each nerve root contributes to a predictable skin territory (dermatome). C5 = lateral arm (badge area); C6 = lateral forearm and thumb; C7 = middle finger; C8 = little finger; T1 = medial forearm. When a patient reports numbness or tingling in a specific distribution, mapping it to a dermatome versus a peripheral nerve territory helps distinguish a nerve root problem (from disc herniation or foraminal stenosis) from a peripheral nerve entrapment. For example, numbness in the little finger could reflect C8 root compression OR ulnar nerve entrapment — but the pattern of motor involvement and EMG will distinguish them.

Quick Revision

• The shoulder girdle consists of the clavicle and scapula; the glenohumeral joint is the most mobile and most commonly dislocated joint in the body
• Rotator cuff = SITS: Supraspinatus, Infraspinatus, Teres minor, Subscapularis; supraspinatus is most commonly torn
• Radial nerve travels in the spiral (radial) groove of the humerus; midshaft humeral fracture = wrist drop
• Ulnar nerve passes posterior to medial epicondyle; "funny bone" sensation; distal lesion = more pronounced claw than proximal lesion (ulnar paradox)
• Median nerve passes through carpal tunnel with 9 flexor tendons; carpal tunnel syndrome = thenar wasting, weak opposition, lateral 3.5 finger numbness
• Brachial plexus: C5-T1; Erb's palsy (C5-C6) = "waiter's tip"; Klumpke's palsy (C8-T1) = claw hand ± Horner syndrome
• Scaphoid fracture: snuffbox tenderness after FOOSH; may be X-ray negative; risk of avascular necrosis if missed
• Carpal tunnel: roof = flexor retinaculum; contains median nerve and 9 tendons (FDS x4, FDP x4, FPL x1); NOT the ulnar nerve
• Thenar muscles (median nerve): Abductor pollicis brevis, Flexor pollicis brevis, Opponens pollicis — first 3 lumbricals also median
• Anterior forearm = flexors (median + ulnar); posterior forearm = extensors (radial nerve entirely)
• Axillary nerve (C5-C6) supplies deltoid and teres minor; at risk in anterior shoulder dislocation; test regimental badge area
• Clavicle most commonly fractured at middle-outer third junction; axillary artery, brachial plexus at risk with medial fractures

Related Topics

Prerequisites: Introduction to Human Anatomy (directional terminology, body planes), Osteology (bone structure and classification)

Related Topics: Neuroanatomy (brachial plexus detailed pathway), Surface Anatomy (palpable landmarks of upper limb), Gross Anatomy of Thorax (axilla and shoulder girdle articulation with thoracic wall), Orthopedic Surgery (fracture management, rotator cuff repair), General Medicine (nerve entrapment syndromes)

Next Topics: Gross Anatomy of Lower Limb (parallel organization — lumbar/sacral plexus versus brachial plexus), Head and Neck Anatomy (cervical nerve roots contributing to brachial plexus), Neuroanatomy (central nervous system connections from peripheral nerve roots)