MRCS Part B Revision · Anatomy
Forearm 1 — MRCS Part B Anatomy
By Dr Richard Miller, MBChB FRCS · Reviewed
Forearm 1 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 Forearm 1 station
Three prosections of the forearm: the anterior compartment with its arteries and the median nerve, the extensor tendons at the wrist, and the flexor tendons at the wrist. The questions turn on which tendon is which and how to test the nerve beside it.
Siding the specimen
Put the radius lateral (thumb side) and the palm forward. The radial styloid reaches further distally than the ulnar; the ulnar head with its styloid is the prominent knob on the back of the wrist on the little-finger side.
Anterior compartment
Superficial layer from the common flexor origin: pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris. Intermediate: flexor digitorum superficialis. Deep: flexor digitorum profundus, flexor pollicis longus, pronator quadratus. The median nerve supplies all of them except flexor carpi ulnaris and the ulnar half of profundus, which are ulnar; the deep three (lateral half of profundus, pollicis longus, pronator quadratus) take the anterior interosseous branch.
Arteries
The brachial artery divides in the cubital fossa. The radial artery runs under brachioradialis and is palpable lateral to flexor carpi radialis at the wrist. The ulnar artery passes deep to pronator teres and flexor digitorum superficialis to reach the ulnar side, running with the ulnar nerve on its medial side under flexor carpi ulnaris. The common interosseous artery leaves the ulnar artery early and splits into anterior and posterior interosseous arteries either side of the membrane.
Testing the median nerve
Ask the patient to make an “OK” sign (flexor pollicis longus and the index profundus — anterior interosseous), flex the wrist against resistance, and abduct the thumb against resistance with the palm up (abductor pollicis brevis, the reliable motor test in the hand). Sensation is checked over the pulp of the index finger. A lesion at the wrist spares the forearm flexors and the palmar cutaneous branch, which leaves the wrist before the carpal tunnel.
Tendons at the wrist
Flexor side, radial to ulnar: flexor carpi radialis, palmaris longus (absent in about one in seven people, which is what makes it unusual), the median nerve just under and lateral to it, flexor digitorum superficialis, flexor carpi ulnaris with the ulnar nerve and artery lateral to it. Flexor pollicis longus and profundus lie deeper in the tunnel.
Extensor side, in six compartments under the retinaculum, radial to ulnar: (1) abductor pollicis longus and extensor pollicis brevis, (2) extensor carpi radialis longus and brevis, (3) extensor pollicis longus, turning around Lister's tubercle, (4) extensor digitorum and extensor indicis, (5) extensor digiti minimi, (6) extensor carpi ulnaris. The first and third compartments form the borders of the anatomical snuffbox, with the radial artery in its floor.
Images from this station
What are you asked at the Forearm 1 station?
The station runs to 23 questions over nine minutes. These are the questions as they are put to you; the model answers are in the question bank.
- Name and side the above structure
- Identify structures 1-3
- Identify structures 4-6
- Identify arteries 7 and 8
- Identify structures 9 and 10
- Identify arteries 11-13
- Describe how you would test the function of structure 14
- Identify muscles 15-17
- Identify muscles 18-20
- Identify the specimen
- Identify structures 1-4
- What is structure 5?
And 11 more at this station.
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 Forearm 1 station ask?
It opens with "Name and side the above structure" and runs to 23 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