MCQs – Anatomy 2

Modern Study Review (AI-Generated)

High-Yield Summary

This topic is a staple of the Royal College exam, focusing heavily on upper extremity surgical approaches, nerve anatomy, and hip surgical intervals. The single most important trade-off in clinical scenarios is the choice of surgical approach based on safe internervous planes and protection of critical neurovascular structures, especially the radial nerve in humeral fractures and the medial circumflex artery in hip surgery. The examiner often forces a choice between anterior versus posterior approaches to the distal humerus based on brachialis coverage and nerve risk. While classic teaching favors the posterior approach for distal humeral fractures, modern minimally invasive techniques increasingly emphasize nerve monitoring and limited dissection to reduce morbidity.

High-Yield Decision Matrix

Active Recall Q&A

Shoulder and Humerus Approaches

Q: What is the internervous plane used in the posterior approach to the shoulder?
A: Between infraspinatus (innervated by suprascapular nerve) and teres minor (innervated by axillary nerve).
Related Pearl: This muscle-splitting approach preserves nerve function and minimizes muscle denervation risk.

Q: In the posterior approach to the humerus, between which muscles is the dissection performed?
A: Between the lateral and medial heads of the triceps, with the radial nerve and profunda brachii artery running between them.
Related Pearl: Identifying this plane protects the radial nerve during distal humeral fracture fixation.

Q: Why is the posterior approach preferred for distal third humeral fractures?
A: Because the distal 1/3 of the humerus anteriorly is covered by the brachialis muscle, which is difficult to mobilize.
Related Pearl: The posterior approach avoids the brachialis, facilitating safer access to distal fractures.

Q: Where is the radial nerve located at the elbow?
A: Between the brachialis and brachioradialis muscles.
Related Pearl: This location is critical to avoid nerve injury during lateral elbow surgeries.

Nerve Root Anatomy

Q: What are the spinal nerve roots of the musculocutaneous nerve?
A: C4 (occasionally), C5, C6, and C7.
Related Pearl: Variations in root contributions can affect clinical presentations of nerve injury.

Q: What are the spinal nerve roots of the axillary nerve?
A: C5 and C6.
Related Pearl: Axillary nerve injury commonly results in deltoid weakness and sensory loss over the lateral shoulder.

Q: What are the spinal nerve roots of the radial nerve?
A: C5, C6, C7, C8, and T1.
Related Pearl: Radial nerve injuries can cause wrist drop due to extensor muscle paralysis.

Q: What are the spinal nerve roots of the median nerve?
A: C5 (occasionally), C6, C7, C8, and T1.
Related Pearl: Median nerve injury affects wrist and finger flexion and thumb opposition.

Q: What are the spinal nerve roots of the ulnar nerve?
A: C7 (occasionally), C8, and T1.
Related Pearl: Ulnar nerve injury causes claw hand deformity due to intrinsic hand muscle paralysis.

Ulnar and Median Nerve Course

Q: Where does the ulnar nerve pierce the intermuscular septum?
A: About 8–10 cm above the medial epicondyle, running on the anterior surface of the medial head of triceps.
Related Pearl: This is a common site of nerve entrapment or injury during medial elbow surgery.

Q: After piercing the intermuscular septum, through which muscles does the ulnar nerve pass?
A: It pierces the two heads of flexor carpi ulnaris (FCU) and runs deep to flexor digitorum superficialis (FDS) and FCU but superficial to flexor digitorum profundus (FDP).
Related Pearl: Knowledge of this course is essential to avoid nerve injury during forearm surgeries.

Q: How does the median nerve pass relative to the flexor digitorum superficialis (FDS)?
A: It passes under the fibrous arch of FDS and runs between FDS and flexor digitorum profundus (FDP).
Related Pearl: This anatomical relationship is important in pronator syndrome and median nerve entrapment.

Radial Nerve Injury and Reinnervation

Q: Which muscle is the last to recover after radial nerve injury?
A: Extensor indicis proprius, which is distal to the extensor pollicis longus (EPL).
Related Pearl: Delayed recovery of index finger extension can help localize the level of radial nerve injury.

Q: Which muscles show early reinnervation in high radial nerve injury?
A: Brachioradialis and extensor carpi radialis longus (ECRL).
Related Pearl: Early return of these muscles indicates proximal radial nerve recovery.

Q: What are the two main distributions of the posterior interosseous nerve (PIN) after emerging from the supinator?
A: A superficial branch innervating extensor digitorum communis (EDC), extensor digiti minimi (EDMinimi), and extensor carpi ulnaris (ECU); and a deep branch innervating abductor pollicis longus (APL), extensor pollicis longus (EPL), extensor pollicis brevis (EPB), and extensor indicis proprius.
Related Pearl: Understanding this branching helps predict patterns of muscle weakness in PIN palsy.

Q: What is the order of muscle reinnervation after radial nerve injury?
A: First EDC, EDMinimi, ECU (superficial branch muscles), followed by APL, EPL, EPB, and finally extensor indicis proprius (deep branch muscles).
Related Pearl: Index finger extension returns before thumb retropulsion due to earlier EDC reinnervation.

Hip Anatomy and Surgical Approaches

Q: Which artery passes through the ligamentum teres?
A: The posterior branch of the obturator artery.
Related Pearl: This artery contributes to femoral head blood supply and is important in hip preservation surgeries.

Q: What is the superficial interval in the medial Ludloff approach to the hip?
A: Between adductor longus and gracilis, going under adductor longus.
Related Pearl: This interval provides safe access to the medial hip without neurovascular injury.

Q: What is the deep interval in the medial Ludloff approach?
A: Between adductor brevis and adductor magnus, an internervous plane between anterior and posterior branches of the obturator nerve.
Related Pearl: This plane allows exposure of the lesser trochanter and iliopsoas tendon.

Q: How is adductor brevis positioned relative to the obturator nerve branches?
A: It is “sandwiched” between the anterior and posterior divisions of the obturator nerve but is supplied by the anterior branch.
Related Pearl: Careful dissection here prevents obturator nerve injury.

Q: What is the anatomical relationship of the profunda femoris artery to pectineus and iliopsoas?
A: It lies on pectineus, gives off the medial circumflex artery which passes posterior to pectineus and curls behind the iliopsoas tendon.
Related Pearl: The medial circumflex artery is the main blood supply to the femoral head and must be preserved during hip surgery.

Q: What surgical caution is necessary during deep dissection under adductor brevis?
A: The medial circumflex artery is at risk as it lies close to the iliopsoas tendon.
Related Pearl: Injury to this artery can cause avascular necrosis of the femoral head.

Classic Clinical Notes

• Posterior approach to shoulder – muscle splitting (deltoid); then technically internervous between infraspinatus (suprascapular) and teres minor (axillary).

• The posterior approach to the humerus – dissection is between lateral and medial heads of triceps (radial nerve and profundus running between). Remember: the posterior approach is good for more distal humeral fractures, because the distal 1/3 of the humerus at the front is covered by the brachialis which at this level is hard to move out of the way. The posterior approach is limited superiorly by radial nerve – you can always slip the plate underneath it.

• The radial nerve is found between medial and lateral heads of triceps, and at the elbow, between brachialis and brachioradialis.

• Musculocutaneous nerve: (C4), C5,6,7.

• Axillary nerve: C5,6.

• Radial nerve: C5, 6, 7, 8, T1.

• Median nerve: (C5), C6,7,8, T1.

• Ulnar nerve: (C7), C8, T1.

• The ulnar nerve pierces the IM septum about 8-10 cm above the medial epicondyle to run in the posterior compartment, just on the ANTERIOR surface of the medial head of triceps. It then pierces the two heads of FCU to run deep to flexor digitorum superficialis and flexor carpi ulnaris, but superficial to FDP.

• Like the ulnar nerve, the median nerve also passes under the fibrous arch of FDS and runs between FDS and FDP.

• The last muscle to recover from radial nerve injury is extensor indicis proprius. It is actually distal to EPL.

• For high radial nerve injury: order of re-innervation. Complicated question. The brachioradialis and ECRL obvious return first. The PIN goes through supinator and emerges (often giving off ECRB before going through supinator, or ECRB gets it from the superficial branch). As it emerges from the distal end of supinator, there are two main distributions of the PIN – one superficial to the EDC, EDMinimi, and ECU; and one that travels more deep to innervate APL, EPL, EPB, and finally most distally, Ext Indices Proprius. Notice that it looks like EPL might get innervated before EPB. Arguable. In any event, index finger extension will return before thumb retropulsion because EDC is reinnervated before EPL.

• So the order: EDC, EDMinimi, ECU (all the superficial ones); then APL, EPL, EPB, Eindicis (the deep ones).

• Note that EDMinimi is innervated quite high.

• Posterior branch of obturator artery – this is what comes through the ligamentum teres.

• The medial Ludloff approach to the hip: superficial exposure goes under adductor longus (between adductor longus and gracilis). Pectineus is more medial, and lies about at the same level as adductor (though it inserts just anterior to longus on the femur). This interval then gets you onto adductor brevis. The deep dissection then goes UNDER brevis between adductor brevis and adductor magnus which is an internervous plane between the anterior branch of obturator nerve (supplying brevis) and the posterior branch (supplying magnus). By lifting up on brevis and pulling down on magnus, you will see the lesser trochanter with the iliopsoas tendon attachment.. Note that the brevis is sorta “sandwhiched” between the anterior and posterior divisions of the obturator nerve (but is supplied by the anterior).

• The profunda femoris lies on pectineus then curves posteriorly – it gives off the medial circumflex artery, which passes posterior to pectineus and then curls behind the iliopsoas tendon (in close proximity to the tendon!) – YOU HAVE TO WATCH OUT FOR THIS ARTERY WHEN YOU DO THE DEEP DISSECTION. After the superficial dissection, you get between longus and brevis – the artery is in this plane as it heads under iliopsoas. You avoid it here by going deep to brevis (between brevis and magnus), but then you end up exposing iliopsoas tendon in the deep dissection – and the artery is RIGHT THERE!

Last Updated on January 25, 2026 by Christian Veillette