MRCS Part B Revision · Anatomy
Humerus 2 — MRCS Part B Anatomy
By Dr Richard Miller, MBChB FRCS · Reviewed
Humerus 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 Humerus 2 station
The whole humerus and its attachments, with the radial nerve as the clinical thread: it is the nerve that wraps around the bone, so a mid-shaft fracture is the classic cause of wrist drop.
Attachments, proximal to distal
- Greater tubercle: supraspinatus, infraspinatus, teres minor (top to bottom). Lesser tubercle: subscapularis.
- Bicipital groove: pectoralis major on the lateral lip, latissimus dorsi on the floor, teres major on the medial lip — “a lady between two majors”.
- Deltoid tuberosity, lateral mid-shaft: deltoid. Opposite it medially: coracobrachialis.
- Anterior shaft: brachialis. Posterior shaft: lateral and medial heads of triceps, above and below the spiral groove.
- Lateral supracondylar ridge: brachioradialis and extensor carpi radialis longus. Lateral epicondyle: common extensor origin. Medial epicondyle: common flexor origin and pronator teres.
Fracture sites and the nerve at each
Surgical neck — axillary nerve. Mid-shaft and spiral groove — radial nerve. Supracondylar — median nerve and brachial artery (and the anterior interosseous nerve). Medial epicondyle — ulnar nerve.
Course of the radial nerve
It is the continuation of the posterior cord (C5–T1). It leaves the axilla through the lower triangular space with the profunda brachii artery, runs in the spiral groove between the lateral and medial heads of triceps, pierces the lateral intermuscular septum about a hand's breadth above the elbow, and descends between brachialis and brachioradialis to lie in front of the lateral epicondyle. There it divides into the superficial (sensory) branch, which runs under brachioradialis and emerges over the anatomical snuffbox, and the deep branch, which winds through supinator to become the posterior interosseous nerve of the extensor compartment.
Above the elbow it supplies triceps, anconeus, brachioradialis and extensor carpi radialis longus, plus the posterior cutaneous nerves of the arm and forearm.
Assessing the radial nerve
Wrist and finger extension against resistance (a wrist drop means a lesion above the posterior interosseous branch), thumb extension, and sensation over the dorsal first web space, which is the autonomous area. Elbow extension is preserved in a spiral-groove lesion because the triceps branches leave higher.
Common sites of injury
The axilla (crutch palsy), the spiral groove (mid-shaft fracture, “Saturday night palsy” from the arm hung over a chair, or callus after healing), the lateral elbow (Monteggia fracture-dislocation, posterior interosseous entrapment at the arcade of Frohse) and the wrist (superficial branch neuroma after handcuffs or surgery).
Images from this station
What are you asked at the Humerus 2 station?
The station runs to 17 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 the muscles attaching at 1 and 2
- What structures attach at 3-5
- What attach at 6-9?
- What muscle attaches at 9
- Identify structure 10 that runs between attachments 13 and 14
- Identify structures 11 and 12
- Identify the muscle attaching at 13 and 14
- Identify the muscle that attaches at 15. What is its function?
- What is the name given to a fracture running through 16?
- What nerve can be found running around point 17
- Describe the course of the radial nerve from brachial plexus to elbow
And 5 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 Humerus 2 station ask?
It opens with "Name and side the above structure" and runs to 17 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