MRCS Part B Revision · Anatomy
Brachial Plexus 2 — MRCS Part B Anatomy
By Dr Richard Miller, MBChB FRCS · Reviewed
Brachial Plexus 2 is a surgical anatomy station. Three of the seventeen examined stations in the MRCS Part B OSCE are surgical anatomy. The anatomy stations put a prosected specimen, a model or an image in front of you and ask you to identify structures and say what they do, what they relate to and what happens when they are injured.
What you need to know for the Brachial Plexus 2 station
What this station tests
A deeper axillary dissection with the pectoral muscles reflected: the axillary artery and its branches, the axillary vein, the cords of the plexus around the artery, and the nerves that matter in axillary surgery. The last image returns to the root of the neck and the great vessels.
Axillary artery
It continues the subclavian artery from the lateral border of the first rib and becomes the brachial artery at the lower border of teres major. Pectoralis minor crosses in front of it and divides it into three parts, which give one, two and three branches:
- First part: superior thoracic artery.
- Second part, behind pectoralis minor: thoracoacromial trunk and lateral thoracic artery.
- Third part: subscapular artery (which gives the circumflex scapular and thoracodorsal arteries), and the anterior and posterior circumflex humeral arteries.
Axillary vein
Formed where the basilic vein joins the brachial veins at the lower border of teres major, it runs medial to the artery and becomes the subclavian vein at the first rib. The cephalic vein climbs the deltopectoral groove, pierces the clavipectoral fascia and ends in it — a reliable landmark for the deltopectoral approach and for venous access.
Cords and terminal branches
The lateral, medial and posterior cords take their names from their position around the second part of the artery. Below pectoralis minor the terminal branches form an “M” in front of the third part: musculocutaneous laterally, the median nerve in the middle formed by a lateral root and a medial root, and the ulnar nerve medially, with the medial cutaneous nerve of the forearm alongside it. The radial and axillary nerves lie behind the artery, from the posterior cord.
Nerves at risk in axillary surgery
- Long thoracic nerve (C5–C7, straight from the roots) runs down the surface of serratus anterior on the medial wall. Injury wings the scapula.
- Thoracodorsal nerve (C6–C8, posterior cord) runs with the thoracodorsal vessels to latissimus dorsi. It is preserved in axillary clearance, and the same bundle is the pedicle of a latissimus dorsi flap.
- Intercostobrachial nerve (T2) crosses the axilla to the skin of the upper inner arm; dividing it leaves that area numb.
Viva favourites
- Upper trunk injury (C5–C6, Erb): arm adducted and internally rotated, elbow extended, forearm pronated — the “waiter’s tip”.
- Lower trunk injury (C8–T1, Klumpke): a clawed hand from loss of the intrinsic muscles, with Horner’s syndrome when the T1 root is avulsed, because its sympathetic outflow is lost.
- List the branches of the axillary artery by part.
Images from this station
What are you asked at the Brachial Plexus 2 station?
The station runs to 9 questions over nine minutes. These are the questions as they are put to you; the model answers are in the question bank.
- Identify vessels 1-3
- Identify vessels 4-6
- Identify structures 7 and 8
- Identify structures 9-11
- Identify structures 12-14
- Identify structures 15-17
- Identify nerves 18 and 19
- Identify structure 20
- Identify vessels 10-12
How is the anatomy station marked in MRCS Part B?
An anatomy station is marked out of 20, and all 20 marks go to clinical knowledge and its application. No communication, technical-skill or professionalism marks are available in an anatomy bay, which is unusual: in most other stations more than half the marks sit outside your factual knowledge.
FAQ
What does the Brachial Plexus 2 station ask?
It opens with "Identify vessels 1-3" and runs to 9 questions over nine minutes. An anatomy station is marked out of 20, and all 20 marks go to clinical knowledge and its application. No communication, technical-skill or professionalism marks are available in an anatomy bay, which is unusual: in most other stations more than half the marks sit outside your factual knowledge.
How many anatomy stations are there in MRCS Part B?
Three of the seventeen examined stations are surgical anatomy, and two more are surgical pathology. Together they make up the five Anatomy and surgical pathology stations of the Applied Knowledge component.
How are the anatomy stations marked?
Each station is marked out of 20 and all 20 marks are awarded for clinical knowledge and its application. You also receive a separate global rating of pass, borderline or fail for the station.
Are the specimens real?
Yes. Anatomy bays use prosected cadaveric specimens, models and images. Candidates report being shown photographs of specimens as well as the specimens themselves, so practise on real dissection photography rather than diagrams alone.
What happens if I get an early question wrong?
The intercollegiate guidance says that if a wrong answer would affect your performance on later questions at the same station, the examiner gives you the correct answer before moving on. One mistake does not have to cost you the whole bay.
How many stations are in the MRCS Part B OSCE?
Seventeen examined stations of nine minutes each, with a minute to read the task before each one. Two preparation stations and at least one rest station bring the circuit to about twenty, and the exam takes about three and a half hours.
What is the pass mark for MRCS Part B?
There is no published pass mark. The cut score is set separately for Applied Knowledge and Applied Skills, for each circuit, by borderline regression. Published pass rates across the 2024/25 diets ranged from 51% to 66%.
Can I fail a station and still pass?
Yes. There is no rule about how many stations you may fail: the cut score applies to your total mark in each component, so a weak station costs the marks you lost on it and strong stations elsewhere can make them back. Applied Knowledge and Applied Skills are passed separately and must both be passed at the same sitting, so a strong anatomy performance cannot rescue a weak communication one.
Dr Richard Miller, MBChB FRCS
Station summaries are reviewed against the current intercollegiate MRCS syllabus and the published marking blueprint. Guidance changes between diets: check the royal colleges' own pages before relying on a date, a fee or a threshold.
Practise this station
The question bank carries the model answer to every question above, with the rest of the anatomy stations.
More anatomy stations