AN11.1-6 | Arm & Cubital fossa — Gate Quiz

Correct! The radial nerve runs in the posterior compartment of the arm, accompanied by the profunda brachii artery in the spiral (radial) groove on the posterior aspect of the humerus. The anterior compartment contains the musculocutaneous, median, and ulnar nerves.

Posterior compartment of arm: Radial nerve + profunda brachii artery in the spiral groove. Muscles: triceps brachii (3 heads). Anterior compartment: Biceps brachii, brachialis, coracobrachialis; musculocutaneous nerve, median nerve, ulnar nerve, brachial artery.

Incorrect. The radial nerve is in the posterior compartment (spiral groove). The anterior compartment contains: musculocutaneous, median, and ulnar nerves.

Correct! The radial nerve runs in the spiral groove on the posterior aspect of the humerus at the midshaft level. A midshaft humeral fracture injures the radial nerve, causing wrist drop (inability to extend the wrist and fingers) due to paralysis of the extensor muscles.

Radial nerve injury at the spiral groove: wrist drop (extensor paralysis), loss of sensation over dorsum of hand (first web space). Note: triceps is typically spared because the radial nerve branches to it above the groove. Test: ask patient to extend the wrist.

Incorrect. Midshaft humeral fracture → radial nerve (spiral groove) injury → wrist drop. Axillary nerve injury: surgical neck fracture; musculocutaneous: rare; median: elbow/wrist.

Correct! The lateral boundary of the cubital fossa is formed by brachioradialis (a forearm flexor muscle that originates from the lateral supracondylar ridge of the humerus). The medial boundary is pronator teres.

Cubital fossa boundaries: Lateral — brachioradialis. Medial — pronator teres. Superior — imaginary line between epicondyles. Roof — deep fascia + bicipital aponeurosis. Floor — brachialis (medially) + supinator (laterally). Contents (lateral to medial): Radial nerve, Biceps tendon, Brachial artery, Median nerve. Mnemonic: 'Really Bent Badly Medially.'

Incorrect. Lateral boundary = brachioradialis. Medial boundary = pronator teres. Roof = deep fascia + bicipital aponeurosis. Floor = brachialis + supinator.

Correct! The brachial artery runs through the cubital fossa, medial to the biceps tendon. It divides into the radial and ulnar arteries at the apex of the cubital fossa (level of the radial head). Blood pressure measurement uses the brachial artery in the cubital fossa.

Cubital fossa arterial contents: Brachial artery (medial to biceps tendon) divides into radial (lateral) and ulnar (medial) arteries at the apex/neck of the radius level. BP cuff compresses the brachial artery in the arm; Korotkoff sounds are heard over the brachial artery in the cubital fossa.

Incorrect. The brachial artery is the vessel auscultated in the cubital fossa for blood pressure measurement. It lies medial to the biceps tendon.

Correct! The musculocutaneous nerve supplies the three muscles of the anterior compartment: biceps brachii, brachialis, and coracobrachialis. Brachioradialis is supplied by the radial nerve (C5, C6).

Musculocutaneous nerve (C5, C6, C7): B-B-C in the anterior compartment (Biceps brachii, Brachialis, Coracobrachialis). Its continuation as the lateral cutaneous nerve of the forearm supplies the lateral forearm skin. Brachioradialis = radial nerve (despite its flexor action at the elbow).

Incorrect. Musculocutaneous supplies: Biceps, Brachialis, Coracobrachialis. Brachioradialis is a radial nerve muscle. Tip: both musculocutaneous and radial nerve supply C5/C6, but to different muscles.

Correct! The biceps brachii is the most powerful supinator of the forearm (more powerful as a supinator than as a flexor of the elbow). The biceps tendon attaches to the radial tuberosity and rotates the radius laterally during supination.

Biceps brachii: (1) Supination of forearm (most powerful action — attaches to radial tuberosity). (2) Flexion of elbow (especially when forearm is supinated). (3) Weak shoulder flexion. Test supination resistance with elbow at 90° — if weak, suspect biceps or musculocutaneous nerve injury.

Incorrect. The biceps brachii is primarily a supinator (most powerful when the elbow is flexed at 90°). It also flexes the elbow, but supination is its strongest and most specialized action.

Correct! Cubital tunnel syndrome is compression of the ulnar nerve as it passes behind the medial epicondyle of the humerus. The ulnar nerve is the most medially placed structure in the cubital fossa and is vulnerable to compression, especially with prolonged elbow flexion.

Cubital tunnel syndrome: Ulnar nerve compression at the medial epicondyle. Symptoms: ring + little finger tingling (ulnar 1.5 digits), hypothenar wasting, grip weakness, intrinsic muscle weakness, 'ulnar claw' in late stages. Provocative test: sustained elbow flexion for 60 seconds (elbow flexion test).

Incorrect. Tingling in ring and little fingers + cubital fossa pain with elbow flexion = ulnar nerve at the cubital tunnel (behind medial epicondyle). This is the second most common nerve compression syndrome (after carpal tunnel).

Correct! The brachial artery bifurcates into the radial and ulnar arteries at the apex of the cubital fossa, at the level of the neck of the radius (approximately 1 cm distal to the bend of the elbow).

Brachial artery: Begins at lower border of teres major (continuation of axillary). Runs medial to humerus, then anterior in the antecubital region. Bifurcates at the apex of the cubital fossa (neck of radius) into radial (lateral) and ulnar (medial) arteries.

Incorrect. The brachial artery bifurcates at the apex of the cubital fossa, at the level of the neck of the radius.

Correct! 'Saturday night palsy' is a compression injury of the radial nerve in the spiral groove of the humerus, caused by prolonged external compression (e.g., arm over a chair back). Results in wrist drop with spared triceps (branches to triceps arise proximal to the groove).

Saturday night palsy (radial nerve in spiral groove): Wrist drop, loss of finger extension, loss of sensation over dorsum of hand/first web space. Triceps spared. Compare: Crutch palsy = radial nerve in the axilla (triceps also affected). Both cause wrist drop but different triceps involvement.

Incorrect. Saturday night palsy = radial nerve compression at the spiral groove. Key finding: wrist drop with intact triceps (normal elbow extension).

Correct! The radial nerve supplies all three heads of triceps brachii. The branches to the long head and medial head arise in the axilla (proximal to the spiral groove), while the branch to the lateral head arises in the spiral groove. This is why the triceps is spared in mid-arm radial nerve injuries.

Radial nerve supplies all posterior compartment muscles: In the arm — triceps (3 heads), anconeus. In the forearm — via deep (posterior interosseous) and superficial branches: all extensors. The long head of triceps is the only part of the posterior compartment not in the spiral groove.

Incorrect. The radial nerve supplies triceps brachii. Its proximal branches to the long and medial heads arise before the spiral groove, explaining why triceps function is often preserved in spiral groove lesions.