Upper Limb Surgical Anatomy for MRCS Part A

FreeMedSite · MRCS Part A · Anatomy Series · Article 08 · October 2026

Upper Limb Surgical Anatomy for MRCS Part A: Brachial Plexus, Nerve Injuries & Clinical MCQs

A beginner-friendly, clinically applied revision guide. Understand where each nerve travels, predict which movement or sensation is lost after injury, recognise safe surgical planes and consolidate the topic through 30 original five-option MRCS SBAs.

Applied anatomy · Paper 140-point saved checklist30 explained SBAsSaved quiz progress

Why is upper limb anatomy important for MRCS?

The official Intercollegiate MRCS content guide (2021) lists 75 indicative applied anatomy questions in the 180-question Paper 1; upper limb and breast are included within regional limb anatomy. These are indicative blueprint counts, not guaranteed numbers at a particular sitting.

5

Terminal nerves

Musculocutaneous, axillary, radial, median and ulnar: their origin, course, motor functions, sensory fields and lesions.

3

Steps to localise injury

Find the trauma site; test muscle actions; check an autonomous cutaneous region to distinguish nerve level.

Learning method: For each lesion ask: (1) Where is the nerve at risk? (2) What muscle movement is lost? (3) What sensory area changes? (4) Which nearby vessel or operative interval matters? Then test yourself before opening the answers.

Contents

1. Brachial plexus in simple steps 2. Shoulder, axilla and rotator cuff 3. Arm fractures and major nerve injury 4. Cubital fossa and elbow 5. Forearm: median, AIN, PIN and ulnar 6. Carpal tunnel, Guyon canal and scaphoid 7. Hand muscles and bedside tests 8. Surgical approaches and structures at risk 9. High-yield nerve localisation map Saved 40-topic checklist 30 original MRCS MCQs FAQs References and further reading

1. Brachial plexus made easy

The brachial plexus is formed by the anterior rami of C5, C6, C7, C8 and T1. The key framework is roots, trunks, divisions, cords and terminal branches. A nerve can combine fibres from several roots; a single root injury may weaken several different named nerves.

RootsC5–T1

TrunksUpper · Middle · Lower

DivisionsAnterior · Posterior

CordsLateral · Medial · Posterior

BranchesFive major nerves

From roots to cords: the logic

Trunks: Upper C5–6, middle C7, lower C8–T1. Each has an anterior and posterior division. Lateral cord comprises the anterior divisions of the upper and middle trunks; medial cord comes from the anterior division of the lower trunk; posterior cord receives the three posterior divisions. Cords are named relative to the second part of the axillary artery.

Upper trunk · Erb palsy

C5–6 injury (e.g. traction between neck and shoulder). Shoulder abduction and external rotation plus elbow flexion weaken. Classic adducted, internally rotated “waiter-tip” posture.

Lower trunk · Klumpke pattern

C8–T1 injury (e.g. upward traction on arm). Intrinsic hand muscles weaken, often with clawing. A proximal T1 injury may also cause ipsilateral Horner syndrome.

Where do the important branches arise?

From roots

Long thoracic C5–7 → serratus anterior; dorsal scapular typically C5 → rhomboids.

From upper trunk

Suprascapular nerve → supraspinatus and infraspinatus; nerve to subclavius is another upper-trunk branch.

From lateral cord

Musculocutaneous nerve and lateral root of median nerve; lateral pectoral nerve.

From medial cord

Ulnar nerve and medial root of median nerve; medial pectoral and medial cutaneous nerves.

From posterior cord

Axillary and radial nerves; upper/lower subscapular and thoracodorsal nerves.

Exam pearl: The median nerve has two roots, one from lateral cord and one from medial cord. The ulnar nerve comes from medial cord; radial and axillary from posterior cord.

2. Shoulder, axilla, scapula and rotator cuff

Two distinctive injuries dominate clinical MRCS questions: axillary nerve dysfunction after shoulder dislocation and long thoracic nerve dysfunction after axillary surgery. The rotator cuff is essential for dynamic glenohumeral stability and rotational control.

Axillary nerve · C5–6

Posterior cord → quadrangular space → surgical neck. Supplies deltoid and teres minor. Sensation: lateral deltoid “regimental badge”. Suspect after anterior dislocation or proximal humeral injury.

Long thoracic nerve · C5–7

Supplies serratus anterior. Injury produces medial scapular winging on forward wall push and reduced scapular upward rotation. At risk in axillary surgery.

Thoracodorsal nerve

Posterior cord → latissimus dorsi, causing weakness of shoulder extension, adduction and internal rotation if damaged.

Intercostobrachial nerve · T2

Cutaneous nerve crossing axilla. Injury after node dissection produces medial proximal arm/axillary numbness, not scapular winging.

Rotator cuff: SITS and examination

Supraspinatus: initiates abduction and stabilises shoulder (suprascapular nerve). Infraspinatus: external rotation (suprascapular nerve). Teres minor: external rotation (axillary nerve). Subscapularis: internal rotation (upper/lower subscapular nerves). Deltoid is a major abductor, while the scapular stabilisers and cuff work throughout the range.

Common bedside tests include Jobe/empty-can (supraspinatus), resisted external rotation (infraspinatus/teres minor), external rotation lag and lift-off/belly-press (subscapularis). Their performance varies with pain, weakness and coexisting pathology; no single test replaces a full examination.

Three spaces behind the shoulder: do not confuse them

Quadrangular space

Teres minor above, teres major below, long head of triceps medial, humerus lateral. Axillary nerve + posterior circumflex humeral artery.

Triangular space

Teres minor above, teres major below and long triceps head laterally. Circumflex scapular artery.

Triangular interval

Teres major above, long triceps head medially, humerus/lateral triceps laterally. Radial nerve + profunda brachii artery.

3. Arm: fractures, nerves and blood supply

The axillary artery becomes the brachial artery at the inferior border of teres major. The brachial artery runs anteriorly with the median nerve and usually divides near the radial neck in the cubital fossa. The profunda brachii branch accompanies the radial nerve posteriorly.

Surgical neck of humerus

Axillary nerve and posterior circumflex humeral vessels at risk. Look for weakness in abduction and lateral deltoid sensory change.

Middle third of humeral shaft

Radial nerve close to the radial groove. Look for wrist/finger extension weakness and dorsal first-web-space sensory loss. Triceps may be relatively preserved.

Proximal radial nerve lesion

If above triceps branches, elbow extension may also be weak, in addition to wrist/finger extension.

Isolated PIN lesion

Finger/thumb drop with little or no skin sensory deficit. Wrist extension can persist with radial deviation because ECRL is preserved.

Neurological examination after trauma: Document an autonomous sensory point plus a relevant motor test for radial, median and ulnar nerves before and after intervention. If vascular deficit, compartment syndrome or progressive neurological injury is suspected, this requires urgent clinical assessment.

4. Cubital fossa, elbow and clinical injury

The cubital fossa is bounded laterally by brachioradialis, medially by pronator teres and superiorly by a line between humeral epicondyles. Its floor includes brachialis and supinator. The bicipital aponeurosis contributes to the roof over the artery and median nerve.

From lateral to medial: Radial nerve → biceps tendon → brachial artery → median nerve. The mnemonic “TAN” (tendon, artery, nerve) describes the central three, but omits the radial nerve laterally.

Median nerve

Travels medial to the brachial artery in cubital fossa and continues between pronator teres heads; gives off AIN in proximal forearm.

Ulnar nerve

Passes behind medial epicondyle in cubital tunnel—not one of the central cubital fossa contents.

Radial nerve

Divides near lateral elbow into superficial sensory and deep (PIN) components. The deep branch travels through supinator.

Brachial artery

At risk in displaced supracondylar fractures. Assess perfusion and nerve function promptly; compartment syndrome must not be missed.

MRCS trap: A child with an abnormal “OK” pinch after supracondylar injury suggests anterior interosseous nerve dysfunction. A pale, cool, pulseless hand raises urgent concern for arterial compromise—these are separate, potentially simultaneous problems.

5. Forearm: median, anterior interosseous, radial/PIN and ulnar nerves

Median nerve and anterior interosseous nerve

The median nerve supplies most anterior forearm flexors, except flexor carpi ulnaris and the ulnar half of FDP. The anterior interosseous branch supplies FPL, index/middle FDP and pronator quadratus. Its classic injury produces a poor tip-to-tip OK sign, with no cutaneous loss. Thenar muscles are principally supplied by the median recurrent motor branch; the two lateral lumbricals are also median-innervated.

Radial nerve and PIN

The radial nerve supplies triceps and wrist/finger extensors. The PIN is its deep predominantly motor component near supinator; a lesion often preserves superficial radial sensation and may leave wrist extension with radial deviation. The superficial radial nerve is predominantly sensory to the dorsoradial hand, including the first web space.

Ulnar nerve

At elbow it runs posterior to medial epicondyle; in forearm it innervates FCU and ulnar half of FDP. At the hand it supplies most intrinsic muscles including interossei, adductor pollicis, medial two lumbricals and hypothenar muscles. Entrapment at elbow may affect ulnar forearm muscles and dorsal hand sensory fibres; Guyon canal lesions generally spare dorsal cutaneous sensation because that branch originates proximally.

Motor localisation: Thumb IP and index DIP flexion → AIN; finger/thumb extension → PIN; finger abduction/adduction → ulnar nerve; thumb opposition → median nerve; deltoid abduction → axillary nerve.

6. Wrist: carpal tunnel, Guyon canal and anatomical snuffbox

Carpal tunnel

Roof: transverse carpal ligament (flexor retinaculum). Contents: median nerve and nine flexor tendons (four FDS, four FDP, one FPL). The palmar cutaneous median branch travels outside the tunnel, so the thenar palm is usually spared in CTS.

Guyon canal

Ulnar nerve and ulnar artery travel superficially to flexor retinaculum between pisiform and hook of hamate region. May cause ulnar intrinsic motor weakness and palmar ulnar-digit sensory change while sparing the dorsoulnar hand.

What is NOT in the carpal tunnel? The ulnar nerve, ulnar artery, radial artery and flexor carpi radialis tendon (FCR has a separate osteofibrous canal within the retinaculum).

Anatomical snuffbox and scaphoid

Radial border: APL and EPB. Ulnar border: EPL. Floor: scaphoid and trapezium. The radial artery passes through the floor; the superficial radial nerve and cephalic vein lie more superficially. A scaphoid waist fracture can interrupt retrograde blood flow to the proximal pole, causing avascular necrosis.

Dorsal extensor compartments: First = abductor pollicis longus + extensor pollicis brevis (de Quervain). Second = ECRL + ECRB. Third = EPL. Fourth = extensor digitorum + extensor indicis. Fifth = extensor digiti minimi. Sixth = extensor carpi ulnaris.

7. Hand intrinsic muscles, deformities and bedside tests

DAB / PAD

Dorsal interossei abduct fingers; palmar interossei adduct fingers. Both predominantly ulnar nerve.

LOAF

Classic median intrinsic group: lateral two lumbricals, opponens pollicis, abductor pollicis brevis, superficial head of flexor pollicis brevis (anatomical variants exist).

Froment sign

Ulnar adductor pollicis weak → compensatory thumb IP flexion by median FPL when holding paper.

Ulnar claw

MCP hyperextension plus IP flexion of ring/little fingers. A low ulnar lesion can produce a more marked claw than a high lesion (ulnar paradox).

Five essential bedside nerve tests

Axillary

Palpate contracting deltoid during resisted shoulder abduction; test lateral deltoid sensation.

Radial

Resisted wrist/MCP extension; sensory test dorsal first web space.

Median

Thumb opposition or palmar abduction; sensory test index fingertip.

AIN (median branch)

Tip-to-tip OK sign for FPL and index FDP; skin sensation remains normal in isolated lesion.

Ulnar

Resisted finger abduction/adduction and Froment; sensory test little fingertip.

Examiner trap: A positive Froment sign is compensatory thumb IP flexion; AIN palsy causes inability to flex thumb IP/index DIP normally. Both concern pinching, but involve different nerves and muscles.

8. Surgical approaches: which structures are at risk?

These are orientation principles for anatomy questions, not a substitute for operative training or direct supervision.

Deltopectoral approach to proximal humerus

Identify the cephalic vein in the groove between deltoid and pectoralis major; develop the interval and remain aware of the axillary and musculocutaneous nerves deeper. Excessive retraction can threaten brachial plexus structures. Axillary nerve position varies; fixed “safe distances” are not absolute.

AO Surgery Reference: deltopectoral approach.

Humeral shaft exposure

The radial nerve crosses the humeral shaft posteriorly in the spiral groove and pierces the lateral intermuscular septum distally. Its course must be anticipated during fixation of the middle or distal shaft. Do not assume that a percutaneous pin in the middle third has a universally safe corridor.

AO Surgery Reference: humeral shaft lateral approach.

Kocher and Kaplan lateral elbow approaches

Kocher interval: anconeus–extensor carpi ulnaris; a more posterior interval, with the lateral collateral ligament complex potentially at risk. Kaplan interval: extensor carpi radialis brevis–extensor digitorum communis; more anterior, so PIN and capsular anatomy demand attention. Pronate the forearm to shift the PIN relatively away from the field, avoid deep distal dissection and do not blindly place retractors around the radial neck.

AO Surgery Reference: lateral approach to proximal forearm.

9. Rapid MRCS lesion-localisation revision

Shoulder dislocation

Axillary nerve → deltoid weakness + lateral deltoid numbness.

Humeral midshaft

Radial nerve → wrist drop + first dorsal web sensory loss.

Proximal radius / supinator

PIN → finger drop without cutaneous loss; possible radial-deviated wrist extension.

Supracondylar humerus

AIN/median or other nerve injury + potential brachial artery compromise.

Carpal tunnel

Median nerve; lateral digital paraesthesia, thenar palm skin often spared.

Guyon canal

Ulnar nerve; hand intrinsic weakness, dorsoulnar hand sensation often spared.

Axillary clearance

Long thoracic injury = winging; intercostobrachial injury = upper medial arm numbness.

Scaphoid waist injury

Proximal pole has higher AVN susceptibility from retrograde arterial supply.

Practical revision technique: Close your notes and try to explain all eight localisations from a blank sheet. Then answer the MCQs without viewing explanations. Revisit every missed mechanism after 24–48 hours and one week.

10. Upper limb anatomy revision checklist — 40 topics

Tick a concept when you can explain the anatomical relationship and clinical application from memory. Your progress is saved in this browser where storage is permitted.

0 of 40 topics completed

Saved locally on this device when browser storage is available; not synced between devices.

01. Roots C5–T1 and formation of upper/middle/lower trunks 02. Anterior versus posterior divisions and cord formation 03. Five terminal nerves and their cord origins 04. Median nerve lateral and medial roots 05. Erb palsy C5–6 versus Klumpke C8–T1 06. Long thoracic and dorsal scapular branches from roots 07. Suprascapular nerve from upper trunk 08. Posterior cord branches and innervated muscles 09. Deltoid motor test and regimental-badge sensation 10. Axillary nerve after anterior shoulder dislocation 11. Rotator cuff SITS muscles and nerve supply 12. Wall push-up test for long thoracic injury 13. Thoracodorsal versus intercostobrachial nerve 14. Quadrangular space borders and contents 15. Triangular space versus triangular interval contents 16. Cephalic vein in deltopectoral groove 17. Radial nerve course in radial groove 18. High radial palsy versus spiral-groove palsy 19. Brachial artery trajectory and bifurcation 20. Cubital fossa boundaries and contents 21. Ulnar nerve posterior to medial epicondyle 22. Supracondylar fracture nerve and vascular injuries 23. Kocher versus Kaplan intervals and PIN danger 24. AIN muscles FPL/FDP/PQ and OK sign 25. PIN finger drop with intact cutaneous sensation 26. Radial nerve autonomous sensory first web space 27. Median proximal lesion versus carpal tunnel 28. Ulnar injury at elbow versus Guyon canal 29. Musculocutaneous sensory lateral forearm 30. Carpal tunnel roof and nine tendons 31. Median palmar cutaneous branch outside tunnel 32. Guyon canal boundaries and ulnar artery 33. Snuffbox boundaries and contents 34. Scaphoid proximal pole retrograde perfusion 35. First six dorsal extensor compartments 36. LOAF and median intrinsic hand muscles 37. DAB/PAD, Froment sign and ulnar paradox 38. Scapular winging: long thoracic versus accessory nerve 39. Deltopectoral, Kocher and Kaplan surgical approaches 40. Ulnar dorsal cutaneous branch and lesion localisation

Revision recommendation: For each tick, explain a nerve's roots, anatomical course, motor/sensory signs and one related procedure. Do not use the checklist as a substitute for your clinical anatomy atlas.

11. Thirty original MRCS Part A upper limb SBAs

These are original practice questions, not reproduced examination recalls. Each is a five-option single-best-answer clinical scenario with individual distractor explanations, an exam pearl, an examiner trap and an answered viva extension.

Saved practice: Select one option A–E and choose Check answer. The browser stores your selection, marked status, score and question position. Explanation opens after marking when JavaScript works; if scripts are disabled, all questions remain readable.

0 / 30Marked

0Correct

—Accuracy

Question 1 of 30

Brachial plexus

Q01. A baby delivered after shoulder dystocia has an adducted, internally rotated arm, extended elbow and pronated forearm. Which part of the brachial plexus is primarily injured?

A.Lower trunk, C8–T1 B.Middle trunk, C7 C.Upper trunk, C5–C6 D.Posterior cord alone E.Medial cord alone

Full answer, examiner traps and viva

Correct answer: C. Upper trunk, C5–C6

Why it is correct: Excessive separation of the neck and shoulder can stretch C5 and C6 fibres. Weak shoulder abduction/lateral rotation and elbow flexion create the classic Erb palsy (waiter-tip) posture.

Why A is incorrect: This more often produces intrinsic hand weakness and a clawing pattern, not predominantly shoulder and elbow deficits.

Why B is incorrect: An isolated C7 injury cannot explain the combined classic C5/C6 muscle deficits.

Why D is incorrect: Its branches contribute to deltoid and extensor function, but the vignette includes musculocutaneous and suprascapular C5/C6 functions across different cords.

Why E is incorrect: This contributes mainly to the ulnar and part of the median nerve and does not match the proximal shoulder pattern.

Exam pearl: Erb palsy: C5–C6, weak abduction/lateral rotation and elbow flexion.

Examiner trap: A plexus root/trunk lesion can affect muscles supplied by more than one terminal nerve.

Answered viva extension: Which common muscles are weak? Supraspinatus, infraspinatus, deltoid, biceps and brachialis.

Q02. Following forceful upward traction on an abducted arm, a patient develops severe intrinsic hand weakness and clawing of the fingers. What is the likely plexus level?

A.Lower trunk, C8–T1 B.Upper trunk, C5–C6 C.Posterior cord, C5–T1 D.Long thoracic nerve, C5–C7 E.Suprascapular nerve, C5–C6

Full answer, examiner traps and viva

Correct answer: A. Lower trunk, C8–T1

Why it is correct: C8 and T1 fibres contribute to many intrinsic hand muscles through the ulnar and median nerves. Lower trunk traction may cause marked weakness of grip and finger abduction/adduction.

Why B is incorrect: This more commonly causes weak shoulder abduction and elbow flexion.

Why C is incorrect: Posterior cord lesions primarily compromise axillary/radial territory and do not account for the full intrinsic-hand presentation.

Why D is incorrect: This produces serratus anterior weakness and scapular winging, not intrinsic hand palsy.

Why E is incorrect: This produces shoulder abduction initiation and external rotation deficits, not hand clawing.

Exam pearl: Klumpke-type lower plexus injury: C8–T1, hand intrinsic dysfunction.

Examiner trap: Not all claw hands are lower trunk lesions; isolated ulnar injury is common.

Answered viva extension: Why may Horner syndrome accompany a T1 root injury? Nearby sympathetic fibres may also be damaged.

Q03. After axillary lymph-node surgery, a woman has prominent medial scapular winging when pushing her hands against a wall. Which nerve is most likely injured?

A.Thoracodorsal nerve B.Axillary nerve C.Intercostobrachial nerve D.Spinal accessory nerve E.Long thoracic nerve

Full answer, examiner traps and viva

Correct answer: E. Long thoracic nerve

Why it is correct: The long thoracic nerve (C5–C7) innervates serratus anterior, which protracts and stabilises the scapula on the chest wall. Its injury produces medial winging particularly with forward pushing.

Why A is incorrect: Innervates latissimus dorsi; its injury weakens extension, adduction and medial rotation at the shoulder.

Why B is incorrect: Innervates deltoid and teres minor, producing weakness of abduction and lateral shoulder sensory loss.

Why C is incorrect: Mainly sensory to the upper medial arm and axilla, and does not supply serratus anterior.

Why D is incorrect: Innervates trapezius; palsy can wing the scapula but typically shows impaired shoulder shrug and a different pattern of winging.

Exam pearl: Wall push-up causing medial winging = serratus anterior/long thoracic nerve.

Examiner trap: Do not confuse sensory intercostobrachial damage after axillary dissection with long thoracic motor palsy.

Answered viva extension: Which roots form the long thoracic nerve? C5, C6 and C7.

Q04. Following posterior neck trauma a patient struggles to retract the scapula, while serratus anterior function is intact. Injury to which nerve best explains rhomboid paralysis?

A.Long thoracic nerve B.Dorsal scapular nerve C.Thoracodorsal nerve D.Suprascapular nerve E.Accessory nerve

Full answer, examiner traps and viva

Correct answer: B. Dorsal scapular nerve

Why it is correct: The dorsal scapular nerve, usually from C5, supplies rhomboid major/minor and often levator scapulae. Rhomboids retract and help stabilise the scapula.

Why A is incorrect: Supplies serratus anterior, which produces protraction and prevents medial winging.

Why C is incorrect: Supplies latissimus dorsi, not rhomboids.

Why D is incorrect: Supplies supraspinatus/infraspinatus, not rhomboids.

Why E is incorrect: Supplies trapezius and sternocleidomastoid, not rhomboids.

Exam pearl: Dorsal scapular C5 = rhomboids; long thoracic C5–C7 = serratus anterior.

Examiner trap: Rhomboid weakness and trapezius weakness are not interchangeable.

Answered viva extension: What are the rhomboids’ key action and root? Scapular retraction; typically C5.

Q05. An overhead athlete develops isolated suprascapular neuropathy. Which paired muscles are most directly weakened?

A.Deltoid and teres minor B.Subscapularis and teres major C.Biceps and brachialis D.Supraspinatus and infraspinatus E.Serratus anterior and rhomboids

Full answer, examiner traps and viva

Correct answer: D. Supraspinatus and infraspinatus

Why it is correct: The suprascapular nerve (mainly C5–C6), a branch of the upper trunk, supplies supraspinatus and infraspinatus. Weakness affects abduction initiation and external rotation.

Why A is incorrect: These are supplied by the axillary nerve.

Why B is incorrect: These are supplied by the upper/lower subscapular nerves from the posterior cord.

Why C is incorrect: These are primarily musculocutaneous nerve muscles.

Why E is incorrect: These use long thoracic and dorsal scapular nerves respectively.

Exam pearl: Suprascapular nerve supplies both supra- and infraspinatus.

Examiner trap: Not all lateral rotation weakness is axillary nerve injury; infraspinatus matters.

Answered viva extension: Which nerve supplies teres minor? Axillary nerve.

Q06. A patient sustains an anterior shoulder dislocation. After reduction there is impaired deltoid contraction and reduced pinprick sensation over the lateral deltoid. Which nerve was injured?

A.Radial nerve B.Axillary nerve C.Median nerve D.Musculocutaneous nerve E.Ulnar nerve

Full answer, examiner traps and viva

Correct answer: B. Axillary nerve

Why it is correct: The axillary nerve courses around the surgical neck through the quadrangular space and supplies the deltoid, teres minor and superior lateral cutaneous territory of the arm.

Why A is incorrect: A distal arm injury causes wrist/digit extension problems rather than isolated regimental-badge sensory loss.

Why C is incorrect: Affects thumb opposition, forearm flexors and median digit sensation.

Why D is incorrect: Affects elbow flexion/supination and lateral forearm sensation.

Why E is incorrect: Affects intrinsic hand function and medial digit sensation.

Exam pearl: Anterior shoulder dislocation + regimental-badge numbness = axillary nerve.

Examiner trap: Normal elbow flexion does not exclude axillary nerve injury; test deltoid directly.

Answered viva extension: Which artery accompanies this nerve posteriorly? Posterior circumflex humeral artery.

Q07. During posterior shoulder dissection, a vessel and nerve are found between teres minor superiorly, teres major inferiorly, long head of triceps medially and surgical neck laterally. Which pair is expected?

A.Radial nerve and profunda brachii artery B.Circumflex scapular artery and dorsal scapular nerve C.Median nerve and brachial artery D.Axillary nerve and posterior circumflex humeral artery E.Suprascapular nerve and suprascapular artery

Full answer, examiner traps and viva

Correct answer: D. Axillary nerve and posterior circumflex humeral artery

Why it is correct: These structures traverse the quadrangular space. Recognising its four borders helps avoid iatrogenic axillary nerve injury.

Why A is incorrect: These traverse the triangular interval inferior to teres major.

Why B is incorrect: The circumflex scapular artery passes through the triangular space, which does not carry the dorsal scapular nerve as its companion.

Why C is incorrect: These travel in the anterior arm and cubital fossa, not quadrangular space.

Why E is incorrect: They relate to the suprascapular notch rather than this axillary gap.

Exam pearl: Quadrangular space = axillary nerve + posterior circumflex humeral artery.

Examiner trap: Triangular space is not the same as triangular interval.

Answered viva extension: What are the quadrangular space borders? Teres minor, teres major, long triceps head and humerus.

Q08. A surgeon enters the triangular interval inferior to teres major. Which neurovascular structures should be sought?

A.Radial nerve and profunda brachii artery B.Axillary nerve and posterior circumflex humeral artery C.Circumflex scapular artery alone D.Ulnar nerve and superior ulnar collateral artery E.Median nerve and radial artery

Full answer, examiner traps and viva

Correct answer: A. Radial nerve and profunda brachii artery

Why it is correct: The radial nerve with deep brachial (profunda brachii) vessels traverses the triangular interval to reach the posterior arm and radial groove.

Why B is incorrect: Pass through quadrangular space.

Why C is incorrect: Passes through triangular space rather than the triangular interval.

Why D is incorrect: Course around the medial aspect of the distal arm.

Why E is incorrect: Median nerve travels with brachial artery proximally; radial artery branches near the elbow.

Exam pearl: Triangular interval = radial nerve + profunda brachii.

Examiner trap: Do not use the triangular-space vessel (circumflex scapular artery) for the interval.

Answered viva extension: Name the superior boundary of the interval: inferior border of teres major.

Q09. A surgical trainee identifies the circumflex scapular artery passing from the axilla to the posterior scapular region. Through which space does it emerge?

A.Quadrangular space B.Triangular interval C.Triangular space D.Carpal tunnel E.Suprascapular notch

Full answer, examiner traps and viva

Correct answer: C. Triangular space

Why it is correct: The circumflex scapular branch of subscapular artery usually passes through the triangular space bordered by teres minor, teres major and long head of triceps.

Why A is incorrect: Contains axillary nerve and posterior circumflex humeral vessels.

Why B is incorrect: Contains radial nerve and profunda brachii vessels.

Why D is incorrect: A wrist passage for median nerve and nine flexor tendons.

Why E is incorrect: Transmits suprascapular nerve under the transverse scapular ligament; unrelated to circumflex scapular artery.

Exam pearl: Triangular space: circumflex scapular artery; interval: radial nerve; quadrangular: axillary nerve.

Examiner trap: The names are similar but their contents differ.

Answered viva extension: Circumflex scapular arises from which artery? Subscapular artery, usually an axillary artery branch.

Q10. A patient with a closed midshaft humeral fracture develops wrist drop and sensory loss in the dorsal first web space. Which nerve has most likely been injured?

A.Axillary nerve B.Median nerve C.Ulnar nerve D.Musculocutaneous nerve E.Radial nerve in the spiral groove

Full answer, examiner traps and viva

Correct answer: E. Radial nerve in the spiral groove

Why it is correct: The radial nerve courses close to the humerus in the spiral/radial groove. Injury weakens wrist and finger extension and may reduce radial dorsal hand sensation.

Why A is incorrect: Vulnerable near the surgical neck, with deltoid weakness and lateral upper arm numbness.

Why B is incorrect: Causes median forearm/hand deficits, not characteristic wrist drop.

Why C is incorrect: Can cause interossei weakness and clawing; wrist extension is radial.

Why D is incorrect: Primarily supplies arm flexors and lateral forearm skin.

Exam pearl: Midshaft humerus + wrist drop + first-web numbness = radial nerve.

Examiner trap: Triceps may remain functional because branches can leave before a spiral-groove lesion.

Answered viva extension: What is the most reliable radial sensory test area? Dorsal first web space.

Q11. After an axillary compression injury, a patient cannot extend the elbow, wrist or fingers. Where is the lesion most likely situated?

A.Posterior interosseous nerve at supinator B.Superficial radial sensory nerve at wrist C.Median nerve at carpal tunnel D.Proximal radial nerve in the axilla E.Ulnar nerve at Guyon canal

Full answer, examiner traps and viva

Correct answer: D. Proximal radial nerve in the axilla

Why it is correct: A radial nerve lesion proximal to triceps branches can weaken elbow extension as well as distal extensors. More distal radial-groove injuries often preserve substantial triceps power.

Why A is incorrect: This pure-motor deep branch affects finger/thumb extension, not triceps.

Why B is incorrect: This is predominantly cutaneous and does not cause major extensor weakness.

Why C is incorrect: Does not supply the triceps or wrist extensors.

Why E is incorrect: Does not supply elbow extension.

Exam pearl: Weak elbow extension suggests radial injury proximal to triceps motor branching.

Examiner trap: A wrist drop alone does not localise a radial lesion above the elbow.

Answered viva extension: Which cord gives rise to the radial nerve? Posterior cord.

Q12. A patient has inability to extend the metacarpophalangeal joints and thumb after proximal radius surgery. Wrist extension remains possible but deviates radially, and hand sensation is normal. Which nerve is injured?

A.Superficial radial nerve B.Posterior interosseous nerve C.Median nerve D.Ulnar nerve E.Axillary nerve

Full answer, examiner traps and viva

Correct answer: B. Posterior interosseous nerve

Why it is correct: The posterior interosseous nerve is the predominantly motor continuation of the deep radial nerve after the supinator. Extensor carpi radialis longus often remains active, so wrist extension may be preserved with radial deviation and no cutaneous loss.

Why A is incorrect: Is sensory and does not cause finger drop.

Why C is incorrect: Primarily controls forearm flexors, thumb opposition and palmar digit sensation.

Why D is incorrect: Supplies interossei and adductor pollicis, not finger extensors.

Why E is incorrect: Supplies deltoid and teres minor at the shoulder.

Exam pearl: PIN palsy = finger/thumb drop, often wrist extension with radial deviation, no cutaneous deficit.

Examiner trap: Differentiate PIN palsy from a high radial nerve palsy with first-web sensory loss.

Answered viva extension: Where is the PIN especially vulnerable? As it traverses the supinator near the proximal radius.

Q13. A child after a supracondylar humeral injury cannot form a round OK sign because the tips of thumb and index finger remain extended. Sensation is intact. Which nerve is involved?

A.Recurrent motor branch of median nerve B.Deep branch of ulnar nerve C.Posterior interosseous nerve D.Superficial radial nerve E.Anterior interosseous nerve

Full answer, examiner traps and viva

Correct answer: E. Anterior interosseous nerve

Why it is correct: The anterior interosseous branch of the median nerve powers flexor pollicis longus, index/middle FDP and pronator quadratus. The patient cannot flex thumb IP and index DIP normally; it has no cutaneous sensory territory.

Why A is incorrect: Supplies thenar muscles, causing thumb opposition weakness rather than the classic pinch-tip deficit.

Why B is incorrect: Affects interossei and adductor pollicis, often producing positive Froment sign.

Why C is incorrect: Produces finger extension deficits rather than failure of thumb IP/index DIP flexion.

Why D is incorrect: Is cutaneous and does not cause loss of OK-pinch flexion.

Exam pearl: AIN palsy = abnormal OK sign with preserved skin sensation.

Examiner trap: Froment sign (ulnar adductor pollicis weakness) is not the same as AIN pinch-tip weakness.

Answered viva extension: Name three AIN muscles: FPL, radial/index FDP and pronator quadratus.

Q14. A patient with confirmed carpal tunnel syndrome has tingling in index and middle fingers, but normal sensation over the fleshy thenar palm. Which anatomical relationship explains this?

A.Palmar cutaneous median branch travels superficial to the flexor retinaculum B.The thenar palm is supplied entirely by ulnar nerve C.The recurrent median branch is sensory D.The superficial radial nerve passes within the carpal tunnel E.The median nerve carries no palmar cutaneous fibres

Full answer, examiner traps and viva

Correct answer: A. Palmar cutaneous median branch travels superficial to the flexor retinaculum

Why it is correct: This branch arises before the tunnel and reaches the thenar palm outside the tunnel. Isolated tunnel compression therefore generally spares skin over the thenar eminence.

Why B is incorrect: Its normal palmar cutaneous innervation is predominantly median.

Why C is incorrect: The recurrent branch primarily supplies thenar motor function.

Why D is incorrect: It does not pass through the carpal tunnel.

Why E is incorrect: It does; their branch departs proximal to the tunnel.

Exam pearl: Carpal tunnel can spare thenar eminence sensation because palmar cutaneous branch bypasses the tunnel.

Examiner trap: Loss of thenar palmar sensation suggests a more proximal lesion or an additional neuropathy.

Answered viva extension: Which roof forms the carpal tunnel? Flexor retinaculum (transverse carpal ligament).

Q15. During carpal tunnel release, the surgeon reviews the true tunnel contents. Which set correctly lists them?

A.Ulnar nerve, ulnar artery and nine tendons B.Median nerve, flexor carpi radialis and eight flexor tendons C.Median nerve, four FDS, four FDP and one FPL tendon D.Radial artery and extensor pollicis longus E.Median nerve and only four FDS tendons

Full answer, examiner traps and viva

Correct answer: C. Median nerve, four FDS, four FDP and one FPL tendon

Why it is correct: There are nine flexor tendons in the tunnel: four flexor digitorum superficialis, four profundus and one flexor pollicis longus, plus the median nerve.

Why A is incorrect: Ulnar neurovascular bundle passes superficial to the retinaculum in Guyon canal.

Why B is incorrect: FCR travels in its own compartment within the retinaculum, not the main tunnel.

Why D is incorrect: These travel in different dorsal/radial pathways.

Why E is incorrect: The FDP and FPL tendons are also present.

Exam pearl: Carpal tunnel = median nerve + nine flexor tendons; NOT FCR or ulnar nerve.

Examiner trap: The flexor carpi radialis tunnel is separate from the carpal tunnel proper.

Answered viva extension: Which structures attach flexor retinaculum medially? Pisiform and hook of hamate.

Q16. A cyclist develops weak interossei and numbness in the palmar little finger but retains normal sensation over the dorsoulnar hand. Where is the ulnar nerve most likely compressed?

A.Cubital tunnel at elbow B.C8 cervical root alone C.Posterior interosseous nerve D.Median nerve at carpal tunnel E.Guyon canal at the wrist

Full answer, examiner traps and viva

Correct answer: E. Guyon canal at the wrist

Why it is correct: The dorsal cutaneous branch leaves the ulnar nerve in the distal forearm before Guyon canal. A lesion in the canal may spare dorsoulnar sensation while affecting intrinsic hand muscles and palmar ulnar digits.

Why A is incorrect: A more proximal lesion may involve fibres destined for the dorsal cutaneous branch and forearm muscles.

Why B is incorrect: Would generally have a wider myotomal/dermatomal distribution and is not the best isolated canal localisation.

Why C is incorrect: Motor to finger extensors, not ulnar hand cutaneous territory.

Why D is incorrect: Produces radial three-and-a-half-digit symptoms, not selective palmar little-finger loss.

Exam pearl: Dorsal ulnar hand spared in Guyon canal lesions (dorsal branch arises proximally).

Examiner trap: Guyon canal is separate from carpal tunnel.

Answered viva extension: Which artery accompanies ulnar nerve in Guyon canal? Ulnar artery.

Q17. During a paper-grip test a patient compensates by flexing the thumb interphalangeal joint. Weakness of which muscle causes a positive Froment sign?

A.Abductor pollicis brevis B.Extensor pollicis longus C.Adductor pollicis D.Flexor pollicis longus E.Opponens pollicis

Full answer, examiner traps and viva

Correct answer: C. Adductor pollicis

Why it is correct: The ulnar-innervated adductor pollicis normally clamps paper between thumb and index. When weak, median-innervated FPL compensates by flexing the thumb IP joint.

Why A is incorrect: This median thenar muscle abducts the thumb, not the key adductor tested.

Why B is incorrect: Extends thumb IP and does not provide the tested adduction force.

Why D is incorrect: This remains active to produce the compensatory IP flexion.

Why E is incorrect: Produces opposition and is chiefly median-innervated, not the specific failing muscle.

Exam pearl: Froment sign = ulnar adductor pollicis failure; FPL compensation is median-innervated.

Examiner trap: Do not misinterpret flexion of the thumb IP as FPL paralysis—it signifies compensatory activity.

Answered viva extension: Which ulnar hand muscles abduct fingers? Dorsal interossei.

Q18. An isolated ulnar nerve laceration at the wrist produces more obvious clawing of the ring and little fingers than a complete lesion at the elbow. Why?

A.The ulnar nerve innervates all finger extensors at the wrist B.In the proximal lesion, paralysis of ulnar FDP reduces flexion at the distal interphalangeal joints C.The low lesion also paralyses biceps D.Proximal ulnar injury always preserves intrinsic hand muscles E.The low lesion paralyses flexor pollicis longus

Full answer, examiner traps and viva

Correct answer: B. In the proximal lesion, paralysis of ulnar FDP reduces flexion at the distal interphalangeal joints

Why it is correct: The high ulnar lesion also denervates the ulnar half of FDP, reducing the distal interphalangeal flexion component of the claw deformity. A distal injury preserves FDP and so may appear more clawed.

Why A is incorrect: Extensor digitorum is radial/PIN innervated, not ulnar.

Why C is incorrect: Biceps is musculocutaneous-innervated.

Why D is incorrect: It does not: interossei are weak at both levels.

Why E is incorrect: FPL is median/AIN supplied; it is generally preserved.

Exam pearl: Ulnar paradox: distal ulnar injury may cause a more dramatic claw.

Examiner trap: Do not assume more clawing always indicates a higher or more severe ulnar lesion.

Answered viva extension: Which FDP slips are usually ulnar innervated? Ring and little fingers.

Q19. A penetrating injury to coracobrachialis leaves weakened elbow flexion and reduced sensation along the lateral forearm. Which nerve is most likely injured?

A.Axillary nerve B.Radial nerve C.Median nerve D.Musculocutaneous nerve E.Ulnar nerve

Full answer, examiner traps and viva

Correct answer: D. Musculocutaneous nerve

Why it is correct: This nerve pierces coracobrachialis, supplies anterior arm muscles including biceps and brachialis, then continues as the lateral cutaneous nerve of the forearm.

Why A is incorrect: Shoulder/deltoid dysfunction and lateral deltoid sensory deficit are characteristic.

Why B is incorrect: Supplies triceps and wrist/finger extensors and dorsal radial hand skin.

Why C is incorrect: Supplies many forearm flexors and radial digit sensation, not typical lateral forearm skin.

Why E is incorrect: Supplies intrinsic hand muscles and medial digits, not lateral forearm sensation.

Exam pearl: Coracobrachialis pierced by musculocutaneous; terminal cutaneous field is lateral forearm.

Examiner trap: A C5/C6 radiculopathy could overlap, but a focal penetrating lesion at coracobrachialis favours the peripheral nerve.

Answered viva extension: Which cord gives rise to musculocutaneous nerve? Lateral cord.

Q20. After breast and axillary lymph-node surgery, a patient has numbness of the axilla and upper medial arm without motor weakness. Which nerve is most likely injured?

A.Intercostobrachial nerve (T2) B.Long thoracic nerve C.Thoracodorsal nerve D.Axillary nerve E.Musculocutaneous nerve

Full answer, examiner traps and viva

Correct answer: A. Intercostobrachial nerve (T2)

Why it is correct: The intercostobrachial nerve is generally the lateral cutaneous branch of the second intercostal nerve and conveys sensation from the axilla and medial proximal arm.

Why B is incorrect: Motor supply to serratus anterior; injury causes winging.

Why C is incorrect: Motor supply to latissimus dorsi, affecting shoulder movements rather than cutaneous sensation.

Why D is incorrect: Carries lateral deltoid cutaneous and deltoid motor fibres, not isolated medial upper-arm sensation.

Why E is incorrect: Its terminal cutaneous branch supplies lateral forearm, not medial upper arm.

Exam pearl: Intercostobrachial T2 = medial upper-arm sensation after axillary surgery.

Examiner trap: Do not confuse it with the long thoracic nerve in axillary surgery.

Answered viva extension: What causes post-axillary surgery winging? Long thoracic nerve/serratus anterior injury.

Q21. While palpating the cubital fossa, a trainee feels the brachial pulse immediately medial to the distal biceps tendon. Which nerve lies medial to the brachial artery there?

A.Median nerve B.Ulnar nerve C.Radial nerve D.Musculocutaneous nerve E.Axillary nerve

Full answer, examiner traps and viva

Correct answer: A. Median nerve

Why it is correct: Within the cubital fossa the classic central structures run lateral to medial as biceps tendon, brachial artery and median nerve. The radial nerve lies further laterally.

Why B is incorrect: Runs posterior to the medial epicondyle and is not a normal central cubital fossa content.

Why C is incorrect: Lies to the lateral side of biceps tendon.

Why D is incorrect: Terminates as lateral cutaneous nerve of the forearm, not medial to the artery.

Why E is incorrect: Is around the shoulder surgical neck, far proximal to cubital fossa.

Exam pearl: Cubital fossa: radial nerve, biceps tendon, brachial artery, median nerve (lateral to medial).

Examiner trap: TAN omits the radial nerve lateral to the biceps tendon.

Answered viva extension: What covers brachial artery anteriorly? Bicipital aponeurosis contributes to the fossa roof.

Q22. A child with an extension-type supracondylar fracture has a weak radial pulse and a pale, cool hand. Which artery is at greatest immediate risk?

A.Axillary artery B.Profunda brachii artery C.Posterior circumflex humeral artery D.Ulnar artery at Guyon canal E.Brachial artery

Full answer, examiner traps and viva

Correct answer: E. Brachial artery

Why it is correct: The brachial artery crosses the anterior elbow immediately proximal to its division into radial and ulnar arteries and is vulnerable to displacement or entrapment by supracondylar fractures.

Why A is incorrect: Situated proximal to teres major and unaffected directly by distal humeral fracture in this vignette.

Why B is incorrect: Travels with radial nerve in the posterior arm and spiral groove, away from the anterior distal fracture mechanism.

Why C is incorrect: Related to surgical neck and quadrangular space.

Why D is incorrect: Distal wrist vessel and not the principal threatened trunk in the supracondylar region.

Exam pearl: Supracondylar fracture + vascular compromise = assess brachial artery urgently.

Examiner trap: This clinical scenario requires urgent neurovascular assessment, not only naming the vessel.

Answered viva extension: What nerve is often associated with extension-type fractures? Median/AIN can be involved; document all nerves.

Q23. A patient has median-distribution paraesthesia with tenderness over pronator teres and reduced cutaneous sensation over the thenar palm. Which site best explains both findings?

A.Isolated carpal tunnel syndrome B.Guyon canal ulnar entrapment C.Median nerve compression in the proximal forearm (pronator syndrome) D.Posterior interosseous entrapment E.Superficial radial neuritis

Full answer, examiner traps and viva

Correct answer: C. Median nerve compression in the proximal forearm (pronator syndrome)

Why it is correct: Proximal median entrapment occurs before the palmar cutaneous branch leaves the nerve, so thenar palm sensation can be affected, unlike typical isolated carpal tunnel syndrome.

Why A is incorrect: The palmar cutaneous branch passes outside the tunnel and thenar skin is usually spared.

Why B is incorrect: Produces ulnar digit and intrinsic hand findings.

Why D is incorrect: Causes finger extension weakness without a cutaneous median deficit.

Why E is incorrect: Produces dorsoradial sensory symptoms, not thenar palm/median digit distribution.

Exam pearl: Thenar palm sensory loss points proximal to carpal tunnel in median neuropathy.

Examiner trap: Thenar muscle wasting can occur in severe CTS despite spared thenar SKIN sensation.

Answered viva extension: Which branch supplies skin over thenar eminence? Palmar cutaneous branch of median nerve.

Q24. The brachial artery normally divides into radial and ulnar arteries at which anatomical location?

A.Within the quadrangular space B.Under the transverse carpal ligament C.At the surgical neck of the humerus D.Near the apex of the cubital fossa, approximately at radial neck level E.Between anterior and middle scalene muscles

Full answer, examiner traps and viva

Correct answer: D. Near the apex of the cubital fossa, approximately at radial neck level

Why it is correct: The brachial artery typically divides opposite the neck of the radius near the cubital fossa apex, although high bifurcation variants occur.

Why A is incorrect: The axillary artery is located proximally; brachial artery bifurcation is distal.

Why B is incorrect: This is the wrist flexor retinaculum, unrelated to brachial bifurcation.

Why C is incorrect: Brachial artery begins around teres major, not divide at surgical neck.

Why E is incorrect: The subclavian artery and plexus roots pass here, not brachial bifurcation.

Exam pearl: Brachial artery divides at the cubital fossa, opposite the radial neck.

Examiner trap: Arterial variants occur; avoid assuming identical bifurcation levels in every patient.

Answered viva extension: Which artery supplies the deep palmar arch predominantly? Radial artery.

Q25. A clinician palpates the anatomical snuffbox after a fall on the outstretched hand. Which artery normally traverses its floor?

A.Ulnar artery B.Radial artery C.Brachial artery D.Anterior interosseous artery E.Posterior circumflex humeral artery

Full answer, examiner traps and viva

Correct answer: B. Radial artery

Why it is correct: The radial artery courses across the scaphoid and trapezium in the snuffbox and contributes branches to carpal and scaphoid circulation.

Why A is incorrect: Travels at the volar ulnar wrist into Guyon canal.

Why C is incorrect: Terminates near the elbow.

Why D is incorrect: Travels deep along the interosseous membrane in the forearm.

Why E is incorrect: Crosses the posterior shoulder in the quadrangular space.

Exam pearl: Snuffbox floor: scaphoid/trapezium; radial artery traverses it.

Examiner trap: Superficial radial nerve and cephalic vein are more superficial, not the principal artery on the floor.

Answered viva extension: What borders the snuffbox? APL/EPB radially; EPL ulnarly.

Q26. A scaphoid waist fracture is initially missed. Which fragment is particularly at risk of avascular necrosis because of its vascular arrangement?

A.Distal tubercle only B.Trapezium C.Pisiform D.Hamate hook E.Proximal pole

Full answer, examiner traps and viva

Correct answer: E. Proximal pole

Why it is correct: Much of the scaphoid blood supply enters distally/dorsally from radial artery branches and flows retrograde towards the proximal pole. Waist fractures can interrupt inflow to the proximal segment.

Why A is incorrect: The distal portion has relatively direct arterial inflow and usually lower AVN risk.

Why B is incorrect: A different carpal bone, not the scaphoid pole distal to the fracture.

Why C is incorrect: Separate ulnar carpal bone with a different vascular pattern.

Why D is incorrect: A separate carpal structure; not affected by scaphoid waist retrograde supply.

Exam pearl: Scaphoid waist fracture: proximal pole AVN risk due to retrograde circulation.

Examiner trap: Negative initial X-rays do not exclude an occult scaphoid fracture; choose imaging/immobilisation appropriately.

Answered viva extension: Which major artery contributes scaphoid branches? Radial artery.

Q27. A postpartum patient has radial-sided wrist pain, worse when lifting an infant, and tenderness over the radial styloid. Which tendons occupy the implicated first dorsal extensor compartment?

A.Extensor pollicis longus alone B.Extensor carpi radialis longus and brevis C.Abductor pollicis longus and extensor pollicis brevis D.Extensor digitorum and extensor indicis E.Extensor carpi ulnaris

Full answer, examiner traps and viva

Correct answer: C. Abductor pollicis longus and extensor pollicis brevis

Why it is correct: De Quervain tenosynovitis affects the first extensor compartment, usually APL and EPB, adjacent to the radial styloid.

Why A is incorrect: EPL occupies the third compartment and forms the ulnar border of the snuffbox.

Why B is incorrect: These are in the second dorsal compartment.

Why D is incorrect: These occupy the fourth dorsal compartment.

Why E is incorrect: ECU runs in the sixth dorsal compartment at the ulnar wrist.

Exam pearl: 1st dorsal compartment = APL + EPB; 3rd = EPL.

Examiner trap: Radial styloid tenosynovitis is not identical to scaphoid fracture; examine mechanism and bony tenderness.

Answered viva extension: Which tendon forms the ulnar snuffbox boundary? EPL.

Q28. A surgeon uses a lateral approach to the radial head. Which forearm position moves the posterior interosseous nerve relatively away from the operative field?

A.Full pronation B.Full supination C.Neutral rotation D.Maximal wrist flexion alone E.Shoulder external rotation alone

Full answer, examiner traps and viva

Correct answer: A. Full pronation

Why it is correct: With pronation, the PIN within the supinator moves further from common lateral exposure planes. AO guidance emphasises pronation plus careful limitation of distal dissection and retractor placement.

Why B is incorrect: This generally brings the PIN closer to the exposure plane than pronation.

Why C is incorrect: Does not provide the maximal relative displacement achieved by full pronation.

Why D is incorrect: Does not reliably protect a nerve near the supinator/radial neck.

Why E is incorrect: Does not displace PIN away from the proximal forearm operative site.

Exam pearl: Lateral radial head approach: pronation helps protect PIN; no blind retractors around radial neck.

Examiner trap: Pronation reduces risk but does not guarantee safety at excessive distal dissection.

Answered viva extension: Name Kocher interval: anconeus and extensor carpi ulnaris.

Q29. During the standard deltopectoral approach to the proximal humerus, a vein marks the interval between deltoid and pectoralis major. Which vein is it?

A.Basilic vein B.Axillary vein C.Median cubital vein D.Cephalic vein E.External jugular vein

Full answer, examiner traps and viva

Correct answer: D. Cephalic vein

Why it is correct: The cephalic vein ascends in the deltopectoral groove and is an important superficial landmark in the approach. Surgeons preserve or mobilise it carefully.

Why A is incorrect: Ascends in the medial arm; not the deltopectoral groove landmark.

Why B is incorrect: Deep axillary structure, not the superficial intermuscular groove vein.

Why C is incorrect: Superficial venous bridge at anterior elbow.

Why E is incorrect: Located in the neck, unrelated to the deltopectoral interval.

Exam pearl: Deltopectoral interval: cephalic vein marks the plane.

Examiner trap: The surgical approach is not through deltoid fibres as a first step; identify deltopectoral plane.

Answered viva extension: Which nearby nerves need protection deeper? Axillary and musculocutaneous nerves, plus plexus with excessive retraction.

Q30. A patient with a severe T1 root avulsion has ipsilateral ptosis, miosis and facial anhidrosis in addition to hand weakness. What explains the ocular findings?

A.Axillary nerve palsy B.Disruption of sympathetic pathway near the T1 root C.Suprascapular nerve palsy D.Median nerve compression at wrist E.Isolated posterior interosseous palsy

Full answer, examiner traps and viva

Correct answer: B. Disruption of sympathetic pathway near the T1 root

Why it is correct: Preganglionic sympathetic fibres from the cervicothoracic region travel close to T1; injury may cause ipsilateral Horner syndrome with a severe lower plexus/root injury.

Why A is incorrect: Does not carry the sympathetic pathway required for Horner syndrome.

Why C is incorrect: Primarily affects rotator cuff muscles.

Why D is incorrect: Cannot cause ipsilateral ptosis and miosis.

Why E is incorrect: Cannot cause Horner syndrome.

Exam pearl: Lower plexus/root injury plus Horner syndrome suggests severe proximal T1 involvement.

Examiner trap: A T1 root avulsion is not equivalent to a distal ulnar nerve lesion, even if both weaken hand muscles.

Answered viva extension: List Horner signs: ptosis, miosis and ipsilateral impaired sweating (pattern varies by lesion).

If browser scripts are disabled, all practice questions and explanations remain visible.

12. MRCS upper limb anatomy FAQs

How much brachial plexus anatomy should I memorise?

Learn roots C5–T1, trunks, the formation of cords, five major nerves, key branches and clinical lesion patterns first. Expand into individual cutaneous territories and operative relationships once those are secure.

What is the key difference between PIN and high radial nerve palsy?

PIN injury causes finger/thumb extension weakness with no cutaneous deficit and often preserved wrist extension. A proximal radial lesion can also affect wrist and sometimes elbow extension and radial sensory function.

How are Froment sign and the OK sign different?

Froment is compensatory thumb IP flexion from ulnar adductor pollicis weakness. Abnormal OK tip pinch is loss of thumb IP/index DIP flexion from median anterior interosseous weakness.

Can carpal tunnel syndrome cause thenar muscle wasting with normal thenar skin sensation?

Yes. The median motor branch to thenar muscles traverses the tunnel, while the median palmar cutaneous branch to thenar skin passes outside it.

Why is the dorsoulnar hand often normal in Guyon canal syndrome?

The dorsal cutaneous ulnar branch commonly leaves the parent nerve several centimetres proximal to the wrist, before the ulnar nerve enters Guyon canal.

Why might the proximal scaphoid pole develop avascular necrosis?

A substantial part of its blood supply flows retrograde from radial artery branches entering more distally, which can be interrupted by a fracture across the waist.

What should I study after this page?

Review brachial plexus lesions and hand-nerve injuries using diagrams, then proceed to shoulder approaches, elbow anatomy, lower-limb anatomy and mixed timed MRCS anatomy questions.

Does ticking the checklist sync to my account?

No. Checklists and quiz answers are stored with browser localStorage when permitted; they are not uploaded to FreeMedSite, and are not synchronised across browsers or devices.

References, further reading and next lessons

1. Intercollegiate MRCS Examinations — candidate guidance (official examination information).
2. Official MRCS candidate content guide (August 2021) — published indicative Paper 1 anatomy blueprint.
3. TeachMeAnatomy — brachial plexus: roots, trunks, cords and terminal branches.
4. TeachMeAnatomy — quadrangular space: nerve and vessel contents.
5. TeachMeAnatomy — cubital fossa: boundaries and neurovascular contents.
6. TeachMeAnatomy — carpal tunnel: nine flexor tendons and median nerve.
7. TeachMeAnatomy — Guyon canal.
8. NCBI Bookshelf — anatomical snuffbox and scaphoid supply.
9. AO Surgery Reference — deltopectoral approach.
10. AO Surgery Reference — lateral elbow/proximal forearm approach.
11. AO Surgery Reference — proximal humeral neurovascular safe zones (positions vary by patient).

Continue the FreeMedSite MRCS series

Complete Part A syllabus

Return to the syllabus to see related anatomy topics and subject priorities.

Open the syllabus guide

12-week study plan

Use a realistic schedule that fits clinical duties, night shifts and longer weekend sessions.

Open the 12-week plan

All MRCS preparation

Browse additional teaching guides, practice quizzes and updates.

Explore MRCS on FreeMedSite

Coming next: inguinal canal and abdominal wall

The next regional anatomy lesson will cover groin anatomy, hernia relations and surgical traps.

Open the surgical anatomy overview

Editorial note: Published for medical education by FreeMedSite in October 2026. Examination allocations are indicative and based on the linked official guide. This site is independent and is not endorsed by the Intercollegiate MRCS Examination Board. Original educational MCQs are not real examination recalls. Review current official policies and practise surgical procedures only within appropriate supervision and local governance.

Return to the start

Continue your MRCS preparation

Follow the published FreeMedSite MRCS lessons in order, or revise a related topic.

Previous articleSurgical Anatomy Made EasyNext articleInguinal Canal & Abdominal WallRelated lessonHead and Neck Surgical AnatomyRelated lessonComplete MRCS Part A Syllabus & Checklist