MRCP Anatomy: Brachial Plexus & Nerve Injuries (MRCP Part 1)

TL;DR

For MRCP Part 1, the brachial plexus is tested through short clinical vignettes that reward pattern recognition rather than rote memorisation. Focus on roots–cords–branches, classic mechanisms of injury, and signature motor–sensory deficits. Mastering a small set of high-yield associations can secure reliable anatomy marks.

Introduction

Anatomy remains one of the most predictable scoring areas in MRCP Part 1, and the brachial plexus is a favourite because it links structure with clinical presentation. Many candidates lose marks by trying to memorise the entire plexus diagram instead of understanding how injuries present in real patients—after fractures, traction injuries, or surgical procedures.

The exam rarely asks you to “draw” the plexus. Instead, it presents a clinical scenario: a fracture at a specific site, a characteristic posture, or a sensory deficit. Your task is to localise the lesion quickly and confidently. This article explains the examinable scope, highlights the most tested subtopics, and shares practical strategies to approach brachial plexus questions efficiently for MRCP Part 1.

For a broader context, see the official MRCP(UK) Part 1 overview and integrate this topic into your overall revision plan.

Quick overview: what MRCP Part 1 expects

The MRCP Part 1 exam tests applied anatomy rather than exhaustive detail. For the brachial plexus, you should be comfortable with:

• Organisation: roots (C5–T1), trunks, divisions, cords, terminal branches

• Key relationships: cords arranged around the axillary artery

• Major terminal nerves: musculocutaneous, axillary, radial, median, ulnar

• Classic lesions: Erb–Duchenne and Klumpke palsy

• Clinical correlations: fractures, traction injuries, and sensory loss patterns

Authoritative anatomy references such as Teach Me Anatomy provide an excellent visual overview if you need a refresher:👉 https://teachmeanatomy.info/upper-limb/nerves/brachial-plexus/

Five most tested subtopics (high-yield)

1. Roots, cords, and branches framework Understand the progression from roots to terminal nerves. Remember that cords are named by their relationship to the axillary artery, not by spinal level.

2. Terminal nerves and hallmark deficits Each major nerve has one or two signature findings that are repeatedly tested.

3. Upper vs lower plexus lesions Erb palsy (C5–C6) versus Klumpke palsy (C8–T1) is a classic comparison.

4. Fracture-related nerve injuries Surgical neck of humerus (axillary), mid-shaft humerus (radial), medial epicondyle (ulnar).

5. Autonomic involvement Horner syndrome with lower trunk/root lesions (T1).

Classic nerve injuries at a glance

Nerve	Common lesion	Key motor deficit	Sensory loss
Axillary	Surgical neck of humerus	Loss of shoulder abduction (15–90°)	“Regimental badge” area
Radial	Mid-shaft humerus fracture	Wrist drop	Dorsal first web space
Median	Carpal tunnel / elbow injury	Thenar wasting, ape hand	Palmar lateral 3½ digits
Ulnar	Medial epicondyle injury	Clawing of 4th–5th digits	Medial 1½ digits
Musculocutaneous	Shoulder trauma	Weak elbow flexion	Lateral forearm

Upper vs lower brachial plexus lesions

Erb–Duchenne palsy (C5–C6)

• Mechanism: Excessive separation of head and shoulder (e.g. obstetric traction).

• Posture: “Waiter’s tip” — adducted, internally rotated arm.

• Muscles affected: Deltoid, biceps, supraspinatus, infraspinatus.

Klumpke palsy (C8–T1)

• Mechanism: Traction on an abducted arm (e.g. grabbing during a fall).

• Posture: Claw hand.

• Association: Horner syndrome due to T1 sympathetic involvement.

How MRCP Part 1 questions are framed

Most questions include:

• A mechanism (fracture, traction, surgery),

• A motor deficit (specific movement lost), and

• A sensory clue.

If you identify the mechanism first, the diagnosis often becomes obvious before analysing finer details. Practising mixed anatomy questions is particularly effective—use reputable question banks such as BMJ OnExamination or Pastest, alongside your core resources.

Mini-case (exam style)

Case: A 52-year-old man sustains a mid-shaft humeral fracture in a road traffic accident. He cannot extend his wrist and reports numbness over the dorsal aspect of the hand between the thumb and index finger.

Answer: Radial nerve injury. Explanation: The radial nerve runs in the spiral groove of the humerus and is vulnerable in mid-shaft fractures. Wrist drop and sensory loss in the first dorsal web space are classic.

Common pitfalls (and how to avoid them)

• Confusing median and ulnar clawing → Remember: ulnar claw is worse at rest; median nerve injury causes thenar wasting.

• Forgetting the axillary nerve → Always assess deltoid function in shoulder injuries.

• Mixing roots with terminal nerves → Horner syndrome suggests a root or lower plexus lesion, not a distal nerve injury.

• Overlearning rare branches → Focus on terminal nerves unless the stem clearly points otherwise.

• Ignoring the mechanism → Mechanism often gives the answer before examination findings.

Practical study-tip checklist

• Learn one key movement and one sensory area per terminal nerve.

• Compare Erb vs Klumpke palsy side by side.

• Practise mixed anatomy MCQs, not isolated topics.

• Use spaced repetition rather than repeated diagram drawing.

• Review mistakes immediately to reinforce patterns.

FAQs

Do I need to memorise the entire brachial plexus diagram for MRCP Part 1?No. Functional understanding and clinical correlations are far more important than perfect recall of every branch.

How commonly is the brachial plexus tested?

It appears regularly because it combines anatomy with neurology and trauma, making it ideal for vignette-based questions.

What is the single most important exam tip?

Use the mechanism of injury to localise the lesion before analysing deficits.

Are rare nerves like the long thoracic nerve examinable?

Occasionally, usually via a classic sign such as winged scapula rather than detailed anatomy.

What resources are best for revision?

TeachMeAnatomy for structure, standard anatomy texts like Gray’s Anatomy for Students, and high-quality MRCP question banks.

Ready to start?

The brachial plexus is a high-yield topic in MRCP Part 1 because it rewards applied understanding over memorisation. By focusing on classic injury patterns, hallmark deficits, and common traps, you can convert anatomy revision into dependable exam marks.

Sources

• MRCP(UK). Part 1 Examination Information. https://www.mrcpuk.org/mrcpuk-examinations/part-1

• Teach Me Anatomy. The Brachial Plexus. https://teachmeanatomy.info/upper-limb/nerves/brachial-plexus/

• Drake RL, Vogl W, Mitchell AWM. Gray’s Anatomy for Students.