MRCS Part B Revision · Anatomy
Wrist — MRCS Part B Anatomy
By Dr Richard Miller, MBChB FRCS · Reviewed
Wrist 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 Wrist station
A wrist prosection and a clinical scenario on the median nerve. The bones and the six extensor compartments come first; the nerve questions are where marks are won or lost.
Bones and joints
Proximal carpal row: scaphoid, lunate, triquetrum, pisiform. Distal row: trapezium, trapezoid, capitate, hamate. The radiocarpal joint is between the distal radius and the articular disc above and the scaphoid, lunate and triquetrum below; the ulna does not reach the carpus. The distal radio-ulnar joint, with the triangular fibrocartilage between the ulnar head and the radial notch, is where pronation and supination happen. The scaphoid crosses both rows, which is why it fractures, and its blood supply enters distally, which is why the proximal pole dies.
Extensor compartments, radial to ulnar
- Abductor pollicis longus and extensor pollicis brevis (de Quervain's).
- Extensor carpi radialis longus and brevis.
- Extensor pollicis longus, around Lister's tubercle (ruptures after distal radius fractures).
- Extensor digitorum and extensor indicis.
- Extensor digiti minimi.
- Extensor carpi ulnaris.
The flexor retinaculum attaches to the scaphoid tubercle and trapezium ridge laterally and the pisiform and hook of hamate medially, converting the carpal groove into the carpal tunnel.
The median nerve
Roots C5–T1, from the lateral and medial cords, which join in front of the third part of the axillary artery. It runs down the arm lateral to the brachial artery, crosses in front of it to lie medial in the cubital fossa, passes between the heads of pronator teres and under the arch of flexor digitorum superficialis, gives the anterior interosseous nerve, and runs between superficialis and flexor carpi radialis to the wrist, where it enters the carpal tunnel deep to the retinaculum. The palmar cutaneous branch leaves about 5 cm above the wrist and passes over the retinaculum.
Forearm: all the flexors except flexor carpi ulnaris and the ulnar half of profundus. Hand: the LOAF muscles — lateral two lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis — and sensation to the palmar thumb, index, middle and radial ring finger, with the dorsal fingertips.
Assessing it after a volar plate
Two weeks after surgery, paraesthesia in the radial digits is carpal tunnel syndrome until proved otherwise: swelling or a prominent plate under the nerve. Test sensation on the index pulp and compare it with the little finger (ulnar) and the thenar eminence (palmar cutaneous branch, spared in carpal tunnel syndrome). Test motor power by thumb abduction against resistance with the palm flat and by opposition to the little finger. Tinel's and Phalen's tests support the diagnosis. Persistent symptoms need the plate checked and the tunnel decompressed rather than watched.
Images from this station
What are you asked at the Wrist station?
The station runs to 20 questions over nine minutes. These are the questions as they are put to you; the model answers are in the question bank.
- Identify the bony structures 1 and 2
- Identify bony structures 3-5
- Identify structures 6 and 7
- Identify structures 8 and 9
- Identify structure 10
- Identify the tendons that run in areas 11 and 12
- Identify the tendons that run in areas 18 and 19
- Identify the tendons that run in areas 15-17
- Identify the tendons that run in areas 13 and 14
- What attaches at area 20?
- Demonstrate/describe how you would assess the median nerve
- You are asked to review a 66 year old lady who presents with parasthesia in her radial two digits two weeks following a difficult right wrist volar locking plate. Demonstrate/describe how you would assess the median nerve
And 8 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 Wrist station ask?
It opens with "Identify the bony structures 1 and 2" and runs to 20 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