Upper limb

Relationships, supply, levels, and what happens when each fails.

• The brachial plexus — roots, trunks, divisions, cords, branches. The ventral rami of C5–T1 (the roots) emerge between the anterior and middle scalenes and join into three trunks in the posterior triangle of the neck: upper (C5–C6), middle (C7), and lower (C8–T1). Each trunk splits behind the clavicle into an anterior and a posterior division. In the axilla the divisions form three cords, named by where they lie around the second part of the axillary artery: the lateral cord (anterior divisions of the upper and middle trunks), the medial cord (anterior division of the lower trunk), and the posterior cord (all three posterior divisions). The cords end in five terminal branches: musculocutaneous (lateral cord), median (lateral and medial cords together), ulnar (medial cord), and axillary and radial (posterior cord). Anterior divisions supply flexors; posterior divisions supply extensors.
• The plexus's smaller branches. From the roots: the dorsal scapular nerve (C5; levator scapulae and the rhomboids) and the long thoracic nerve (C5–C7; serratus anterior). From the upper trunk: the suprascapular nerve (supraspinatus and infraspinatus) and the nerve to subclavius. From the lateral cord: the lateral pectoral nerve. From the medial cord: the medial pectoral nerve and the medial cutaneous nerves of the arm and forearm. From the posterior cord: the upper and lower subscapular nerves (subscapularis; the lower also supplies teres major) and the thoracodorsal nerve (latissimus dorsi).
• The shoulder girdle and scapular movement. The upper limb's only bony attachment to the trunk is the sternoclavicular joint; everything else is muscle. Trapezius (CN XI) elevates, retracts, and upwardly rotates the scapula; levator scapulae and the rhomboids (dorsal scapular nerve) elevate and retract it; serratus anterior (long thoracic nerve) protracts it and holds it against the chest wall, and with trapezius rotates the glenoid upward so the arm can rise above the horizontal. Latissimus dorsi (thoracodorsal nerve) extends, adducts, and medially rotates the humerus.
• The glenohumeral joint and the rotator cuff. A large humeral head on a shallow glenoid, deepened slightly by the labrum, buys range at the cost of stability — the shoulder dislocates more than any other major joint, almost always anteriorly and inferiorly. Stability comes from the four rotator cuff muscles (SITS): supraspinatus (suprascapular nerve; initiates abduction, then assists the deltoid), infraspinatus (suprascapular nerve; lateral rotation), teres minor (axillary nerve; lateral rotation), and subscapularis (upper and lower subscapular nerves; medial rotation). The first three insert on the greater tubercle; subscapularis on the lesser. The deltoid (axillary nerve) is the main abductor once the movement has begun.
• The axilla and the axillary artery. The axilla is a pyramid-shaped passage between the neck and the arm, holding the axillary artery and vein, the cords and branches of the brachial plexus, and the axillary lymph nodes that drain most of the breast. The axillary artery runs from the lateral border of the first rib to the inferior border of teres major and is divided into three parts by pectoralis minor: part 1 (superior thoracic artery), part 2 (thoracoacromial trunk, lateral thoracic artery), and part 3 (subscapular artery, the largest branch, and the anterior and posterior circumflex humeral arteries) — one, two, and three branches. Past teres major it becomes the brachial artery.
• The arm — two compartments, two nerves. The ANTERIOR compartment (biceps brachii, brachialis, coracobrachialis) flexes the elbow and is supplied by the musculocutaneous nerve, which pierces coracobrachialis and ends as the lateral cutaneous nerve of the forearm. The POSTERIOR compartment (triceps brachii) extends the elbow and is supplied by the radial nerve, which spirals around the back of the humerus in the radial groove with the profunda brachii artery. The median nerve and brachial artery run together down the medial arm without branching there; the ulnar nerve passes behind the medial epicondyle, where it is the 'funny bone'.
• The cubital fossa. A triangle in front of the elbow bounded by a line between the epicondyles above, brachioradialis laterally, and pronator teres medially. From lateral to medial it holds the biceps tendon, the brachial artery, and the median nerve; the radial nerve lies just lateral, deep to brachioradialis, where it divides into superficial and deep branches. The brachial artery divides into the radial and ulnar arteries at about the level of the radial neck. The bicipital aponeurosis roofs over the artery and nerve; the median cubital vein crosses superficial to it — the usual venipuncture site.
• The elbow and the forearm joints. The elbow is a hinge (humeroulnar and humeroradial joints) sharing one capsule with the proximal radioulnar joint, where the radial head turns inside the annular ligament. Pronation and supination happen at the proximal and distal radioulnar joints as the radius rotates around the ulna. Pronator teres and pronator quadratus (median nerve) pronate; supinator (radial nerve) and biceps brachii supinate — biceps most powerfully when the elbow is flexed, which is why screwing in a screw is a right-handed design.
• The anterior forearm — median nerve territory. The flexor-pronator muscles arise largely from the medial epicondyle in three layers: superficial (pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris), intermediate (flexor digitorum superficialis), and deep (flexor digitorum profundus, flexor pollicis longus, pronator quadratus). All are supplied by the median nerve or its anterior interosseous branch EXCEPT flexor carpi ulnaris and the medial (ulnar) half of flexor digitorum profundus, which are ulnar nerve. The anterior interosseous nerve supplies flexor pollicis longus, the lateral half of profundus, and pronator quadratus, and has no skin territory.
• The posterior forearm — radial nerve territory. The extensor-supinator muscles arise largely from the lateral epicondyle and are ALL supplied by the radial nerve. Brachioradialis and extensor carpi radialis longus are supplied before the nerve divides; the deep branch then pierces supinator and continues as the posterior interosseous nerve to the remaining extensors (extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, the thumb's long abductor and extensors). The superficial branch is purely sensory to the dorsum of the lateral hand. The anatomical snuffbox lies between abductor pollicis longus and extensor pollicis brevis laterally and extensor pollicis longus medially, with the scaphoid in its floor and the radial artery crossing it.
• The wrist, the carpal tunnel, and Guyon's canal. Eight carpal bones in two rows — scaphoid, lunate, triquetrum, pisiform (proximal, lateral to medial); trapezium, trapezoid, capitate, hamate (distal). The flexor retinaculum bridges them to form the carpal tunnel, which carries nine tendons (four of flexor digitorum superficialis, four of profundus, and flexor pollicis longus) and the median nerve. The palmar cutaneous branch of the median nerve leaves above the wrist and passes OVER the retinaculum, so carpal tunnel syndrome spares the skin of the central palm. The ulnar nerve and artery pass superficial to the retinaculum through Guyon's canal, between the pisiform and the hook of the hamate.
• The hand — the ulnar nerve does the fine work. The median nerve (recurrent branch) supplies the thenar muscles (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis) and the lateral two lumbricals — 'LOAF'. The deep branch of the ulnar nerve supplies everything else: the hypothenar muscles, all the interossei (palmar ADduct, dorsal ABduct — PAD and DAB), the medial two lumbricals, and adductor pollicis. Lumbricals and interossei flex the metacarpophalangeal joints and extend the interphalangeal joints through the extensor expansion. The superficial palmar arch (mainly from the ulnar artery) lies distal to the deep arch (mainly from the radial artery).
• Vessels, dermatomes, and the bedside exam. Arterial chain: subclavian → axillary (at the first rib) → brachial (at teres major) → radial and ulnar (in the cubital fossa) → the palmar arches; the Allen test checks that the ulnar artery alone can fill the hand before the radial is cannulated. Superficial veins: the cephalic vein runs laterally to the deltopectoral groove and the axillary vein; the basilic vein runs medially and joins the brachial veins to form the axillary vein. Dermatomes: C5 lateral arm, C6 lateral forearm and thumb, C7 middle finger, C8 little finger and medial hand, T1 medial forearm. Reflexes: biceps (C5–C6), brachioradialis (C6), triceps (C7). Myotomes: shoulder abduction C5, elbow flexion C5–C6, wrist extension C6, elbow extension C7, finger flexion C8, finger abduction T1.

In the order a dissection meets them — each with the one relationship that identifies it. Your lab's study list is the authority; use this to check yours against.

1. 1Clavicle — S-shaped strut from sternum to acromion; usually breaks in its middle third
2. 2Acromion — lateral end of the scapular spine; the point of the shoulder
3. 3Coracoid process — anterior scapular hook for pectoralis minor, coracobrachialis, and the short head of biceps
4. 4Glenoid cavity — shallow scapular socket for the humeral head, deepened by the labrum
5. 5Supraspinous fossa — above the scapular spine; origin of supraspinatus
6. 6Infraspinous fossa — below the scapular spine; origin of infraspinatus
7. 7Greater tubercle — lateral humeral head; insertion of supraspinatus, infraspinatus, teres minor
8. 8Lesser tubercle — anterior humeral head; insertion of subscapularis
9. 9Intertubercular groove — between the tubercles; carries the tendon of the long head of biceps
10. 10Surgical neck of the humerus — fracture site that endangers the axillary nerve and posterior circumflex humeral artery
11. 11Radial groove — spiral on the posterior humeral shaft for the radial nerve and profunda brachii
12. 12Medial epicondyle — common flexor origin; the ulnar nerve runs behind it
13. 13Lateral epicondyle — common extensor origin; tender in tennis elbow
14. 14Olecranon — proximal ulna; the point of the elbow, where triceps inserts
15. 15Radial head — turns within the annular ligament at the proximal radioulnar joint
16. 16Radial tuberosity — medial proximal radius; insertion of the biceps tendon
17. 17Scaphoid — lateral proximal carpal in the floor of the anatomical snuffbox; the carpal most often fractured
18. 18Pisiform — sesamoid in the flexor carpi ulnaris tendon; medial wall of Guyon's canal
19. 19Hook of the hamate — palpable in the hypothenar base; lateral wall of Guyon's canal
20. 20Trapezius — CN XI; elevates, retracts, and upwardly rotates the scapula
21. 21Latissimus dorsi — thoracodorsal nerve; extends, adducts, and medially rotates the humerus
22. 22Levator scapulae — dorsal scapular nerve; elevates the scapula from the upper cervical transverse processes
23. 23Serratus anterior — long thoracic nerve; protracts the scapula and holds it to the chest wall
24. 24Pectoralis minor — coracoid to ribs 3–5; divides the axillary artery into three parts
25. 25Deltoid — axillary nerve; the main abductor once the movement has begun
26. 26Supraspinatus — suprascapular nerve; initiates abduction; the cuff tendon most often torn
27. 27Infraspinatus — suprascapular nerve; lateral rotator below the scapular spine
28. 28Teres major and minor — minor (axillary nerve) is rotator cuff, major (lower subscapular nerve) is not
29. 29Subscapularis — anterior scapula; the rotator cuff's only medial rotator
30. 30Biceps — biceps brachii; musculocutaneous nerve; flexes the elbow and is the strongest supinator
31. 31Brachialis — deep to biceps on the anterior humerus; the pure elbow flexor
32. 32Coracobrachialis — from the coracoid; pierced by the musculocutaneous nerve
33. 33Triceps — triceps brachii; radial nerve; the posterior arm's elbow extensor, inserting on the olecranon
34. 34Brachioradialis — radial nerve, yet flexes the elbow; lateral border of the cubital fossa
35. 35Pronator teres — the median nerve passes between its two heads; medial border of the cubital fossa
36. 36Flexor carpi radialis — median nerve; the radial pulse lies just lateral to its tendon
37. 37Palmaris longus — superficial midline wrist tendon, absent in some people
38. 38Flexor carpi ulnaris — ulnar nerve; inserts by way of the pisiform
39. 39Flexor digitorum superficialis — median nerve; its tendons split to insert on the middle phalanges
40. 40Flexor digitorum profundus — median and ulnar halves; its tendons insert on the distal phalanges
41. 41Flexor pollicis longus — anterior interosseous nerve; flexes the thumb's interphalangeal joint
42. 42Pronator quadratus — deepest muscle of the distal anterior forearm; the main pronator
43. 43Supinator — wraps the proximal radius; pierced by the deep branch of the radial nerve
44. 44Extensor carpi radialis longus and brevis — wrist extensors to the 2nd and 3rd metacarpals; the brevis origin is tennis elbow
45. 45Extensor digitorum — posterior interosseous nerve; extends the fingers through the extensor expansion
46. 46Abductor pollicis longus — with extensor pollicis brevis, the lateral border of the snuffbox (de Quervain's tendons)
47. 47Extensor pollicis longus — medial border of the snuffbox; hooks around the dorsal radial tubercle
48. 48Thenar eminence — abductor and flexor pollicis brevis plus opponens pollicis; recurrent branch of the median nerve
49. 49Hypothenar eminence — abductor, flexor, and opponens digiti minimi; deep branch of the ulnar nerve
50. 50Adductor pollicis — deep ulnar nerve in the thumb web; the muscle Froment's sign tests
51. 51Lumbricals — arise from the profundus tendons; flex the MCP joints and extend the IP joints
52. 52Interossei — between the metacarpals; ulnar nerve; palmar adduct, dorsal abduct
53. 53Brachial plexus roots — ventral rami of C5–T1, emerging between the anterior and middle scalenes
54. 54Upper trunk — C5 and C6 joining at Erb's point; the injury of a stretched neck and shoulder
55. 55Lower trunk — C8 and T1 over the first rib; the injury of a pulled-up arm
56. 56Lateral cord — gives the musculocutaneous nerve and the lateral root of the median
57. 57Medial cord — gives the ulnar nerve and the medial root of the median
58. 58Posterior cord — behind the axillary artery; gives the axillary and radial nerves
59. 59Long thoracic nerve — on the outer surface of serratus anterior; injury wings the scapula
60. 60Suprascapular nerve — through the suprascapular notch under the transverse scapular ligament
61. 61Thoracodorsal nerve — runs with the thoracodorsal artery into latissimus dorsi
62. 62Musculocutaneous nerve — pierces coracobrachialis; ends as the lateral cutaneous nerve of the forearm
63. 63Axillary nerve — through the quadrangular space around the surgical neck
64. 64Radial nerve — through the triangular interval into the radial groove with profunda brachii
65. 65Median nerve — beside the brachial artery in the arm; through the carpal tunnel into the hand
66. 66Ulnar nerve — behind the medial epicondyle; enters the hand through Guyon's canal
67. 67Anterior interosseous nerve — median branch on the interosseous membrane; motor only
68. 68Posterior interosseous nerve — deep radial branch past supinator; supplies the extensors, no skin
69. 69Recurrent branch of the median nerve — curls into the thenar muscles; the 'million-dollar nerve'
70. 70Axillary artery — first rib to the lower border of teres major, in three parts around pectoralis minor
71. 71Thoracoacromial trunk — second-part branch piercing the clavipectoral fascia
72. 72Lateral thoracic artery — second-part branch along serratus anterior; supplies the lateral breast
73. 73Subscapular artery — the largest axillary branch, from the third part
74. 74Posterior circumflex humeral artery — runs with the axillary nerve through the quadrangular space
75. 75Brachial artery — medial to biceps beside the median nerve; the blood-pressure cuff's artery
76. 76Profunda brachii artery — deep artery of the arm; follows the radial nerve in the radial groove
77. 77Radial artery — pulse lateral to the FCR tendon; crosses the floor of the snuffbox
78. 78Ulnar artery — with the ulnar nerve through Guyon's canal; the main source of the superficial palmar arch
79. 79Superficial palmar arch — mainly ulnar artery; distal to the deep arch, level with the extended thumb's web
80. 80Deep palmar arch — mainly radial artery; lies on the metacarpal bases under the long flexor tendons
81. 81Cephalic vein — lateral; runs in the deltopectoral groove to the axillary vein
82. 82Basilic vein — medial; pierces the deep fascia and joins the brachial veins
83. 83Median cubital vein — crosses the cubital fossa between cephalic and basilic; the usual venipuncture site
84. 84Quadrangular space — teres minor, teres major, long head of triceps, humerus; axillary nerve passes
85. 85Triangular space — teres minor, teres major, long head of triceps; circumflex scapular artery passes
86. 86Triangular interval — below teres major beside the long head of triceps; radial nerve passes
87. 87Cubital fossa — lateral to medial: biceps tendon, brachial artery, median nerve
88. 88Bicipital aponeurosis — fascial band from the biceps tendon roofing the brachial artery and median nerve
89. 89Carpal tunnel — flexor retinaculum roof; nine flexor tendons and the median nerve
90. 90Guyon's canal — between the pisiform and the hook of the hamate; ulnar nerve and artery
91. 91Anatomical snuffbox — radial artery over the scaphoid, between the thumb's extensor tendons
92. 92Extensor expansion — dorsal hood over each finger where the lumbricals and interossei insert

The distinctions that lose points on the practical, year after year.

• Erb's palsy vs Klumpke's palsy. Erb (UPPER trunk, C5–C6): a stretched neck and shoulder — shoulder dystocia or a motorcycle fall — leaves the arm adducted and medially rotated with the elbow extended and the forearm pronated: the 'waiter's tip'. Klumpke (LOWER trunk, C8–T1): an arm yanked upward — a breech delivery, catching a branch — paralyzes the intrinsic hand muscles and gives a claw hand, sometimes with Horner syndrome if the T1 root is torn. Upper is the shoulder; lower is the hand.
• Which way the scapula wings. A long thoracic nerve injury (serratus anterior) lifts the MEDIAL border off the chest, worst when pushing against a wall. A spinal accessory injury (trapezius) gives a drooping shoulder with the scapula shifted laterally and trouble abducting above the horizontal. Same word, different nerve, different exam.
• Where along the radial nerve the lesion sits. In the axilla (a crutch, 'Saturday night palsy' over a chair back) triceps is lost too. At the mid-shaft of the humerus (the radial groove) triceps is usually spared but the wrist drops. At the posterior interosseous nerve, the fingers and thumb can't extend but the wrist still lifts — extensor carpi radialis longus is spared, so it drifts radially — and there is no sensory loss.
• The ulnar paradox. An ulnar lesion at the WRIST claws the ring and little fingers more than one at the ELBOW. Higher up, the ulnar half of flexor digitorum profundus is paralyzed too, so nothing pulls the fingertips into flexion. The more proximal lesion looks less dramatic despite being worse.
• The 'hand of benediction' is a fist, not a resting hand. A proximal median nerve lesion shows when the patient tries to make a FIST: the index and middle fingers stay straight because their profundus and superficialis are lost, while the ring and little fingers flex on their ulnar supply. Ulnar clawing, by contrast, appears at rest with the fingers extended. Students confuse the two because both are described with the same religious image.
• Carpal tunnel spares the central palm. The palmar cutaneous branch of the median nerve leaves above the wrist and passes over the flexor retinaculum, so carpal tunnel syndrome numbs the thumb, index, middle, and radial half of the ring finger but NOT the central palm. Palmar numbness points to a lesion higher up the forearm.
• Who abducts the arm at each angle. Supraspinatus starts abduction, the deltoid carries it to about 90°, and above the horizontal the scapula must rotate upward — trapezius and serratus anterior. A patient who can't START abduction has a supraspinatus problem; one who can't get above shoulder height may have an upward-rotator problem, not a deltoid one.
• Where the axillary artery begins and ends. It becomes the axillary artery at the lateral border of the first rib and the brachial artery at the lower border of teres major; pectoralis minor divides it into three parts with one, two, and three branches. Students name branches correctly but file them under the wrong part — learn the part first, then its branches.

Where this region shows up again — in clinical medicine, on rotations, and on the boards.

• Carpal tunnel syndrome. Compression of the median nerve under the flexor retinaculum: numbness and tingling of the thumb through the radial ring finger, worse at night and with repetitive wrist use, eased by shaking the hand. Phalen's and Tinel's signs support it; thenar wasting and weak thumb abduction mean advanced disease. Associations include pregnancy, hypothyroidism, diabetes, and rheumatoid arthritis. A wrist splint in neutral comes first; nerve conduction studies confirm before surgical release.
• Ulnar neuropathy at the elbow. The ulnar nerve is compressed in the cubital tunnel behind the medial epicondyle, often from leaning on the elbow or sleeping with it flexed: tingling of the little finger and half the ring finger, weak grip, and wasting of the first dorsal interosseous. Froment's sign — the thumb's interphalangeal joint flexes when pinching paper, because flexor pollicis longus (median) substitutes for a weak adductor pollicis — is the bedside test.
• Humerus fractures and the nerve at each level. Surgical neck → axillary nerve (weak abduction, numbness over the lateral shoulder). Mid-shaft → radial nerve in the radial groove (wrist drop). Supracondylar (the classic childhood elbow fracture after a fall on the outstretched hand) → the brachial artery and the median nerve, especially its anterior interosseous branch; a missed arterial injury can end in Volkmann ischemic contracture. Medial epicondyle → ulnar nerve.
• Anterior shoulder dislocation. The humeral head is levered forward and down by abduction plus external rotation; the shoulder looks squared off and the arm is held slightly abducted and externally rotated. Check axillary nerve function — sensation over the lateral shoulder — before AND after reduction. A posterior dislocation, rarer, follows seizures and electric shocks and is easily missed on a single view.
• Rotator cuff tears and impingement. Supraspinatus is the tendon most often torn, by degeneration in older patients or by a fall. A painful arc between about 60° and 120° of abduction suggests impingement under the acromion; the drop-arm test (the arm can't be lowered slowly from 90°) suggests a full-thickness tear, and the empty-can test isolates supraspinatus. Subscapularis tears show as weak internal rotation (lift-off and belly-press tests).
• Scaphoid fracture. A fall on the outstretched hand with tenderness in the anatomical snuffbox is a scaphoid fracture until proven otherwise — the first X-ray is often normal, so immobilize in a thumb spica splint and re-image or get an MRI. The scaphoid's blood enters distally and flows backward, so a waist fracture can starve the proximal pole: avascular necrosis and nonunion.
• Lateral and medial epicondylitis. Tennis elbow is overuse degeneration at the common extensor origin, chiefly extensor carpi radialis brevis: pain over the lateral epicondyle with resisted wrist extension. Golfer's elbow is the same process at the common flexor origin on the medial epicondyle, painful with resisted wrist flexion and pronation. Both are treated first with activity modification and bracing.
• De Quervain tenosynovitis. Inflammation of the abductor pollicis longus and extensor pollicis brevis tendons in the first dorsal compartment at the radial styloid, common in new parents who lift an infant with the thumb spread. Finkelstein's test — the thumb tucked in a fist and the wrist bent toward the ulna — reproduces the pain.
• Radial head subluxation. 'Nursemaid's elbow': a toddler is lifted or swung by the hand, the radial head slips partly out of the annular ligament, and the child refuses to use the arm, holding it slightly flexed and pronated. X-rays are normal; reduction by hyperpronation (or supination with flexion) usually brings back use within minutes.
• Pancoast tumor and the lower trunk. A tumor at the lung apex invades the lower trunk of the plexus and the sympathetic chain next to it: shoulder and medial-arm pain, weakness and wasting of the intrinsic hand muscles, ulnar-side numbness, and an ipsilateral Horner syndrome. Hand weakness plus Horner in a smoker should prompt imaging of the apex.