AN12.1-15 | Forearm & hand — Gate Quiz

Correct! The median nerve is the primary motor nerve of the anterior compartment of the forearm, supplying most of the flexor muscles. The exceptions are: flexor carpi ulnaris (FCU) and the medial half of flexor digitorum profundus (FDP), which are supplied by the ulnar nerve.

Median nerve in forearm: supplies all anterior compartment except FCU and medial FDP (ulnar nerve). The anterior interosseous nerve (branch of median) supplies FPL, lateral FDP, and pronator quadratus. LOAF muscles in hand = median nerve (Lumbricals 1&2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis).

Incorrect. Most anterior forearm muscles are supplied by the median nerve. Exceptions: FCU + medial FDP = ulnar nerve. Posterior forearm = radial nerve.

Correct! Carpal tunnel syndrome is the most common peripheral nerve entrapment. The median nerve is compressed as it passes through the carpal tunnel (bounded by the carpal bones dorsally and the flexor retinaculum anteriorly). Symptoms: tingling in lateral 3.5 digits (median nerve territory), thenar wasting.

Carpal tunnel contents: Median nerve + 9 tendons (FDS ×4, FDP ×4, FPL ×1). The ulnar nerve is NOT in the carpal tunnel — it passes through Guyon's canal medially. Tests: Phalen's (wrist flexion 60 sec), Tinel's (percussion over tunnel). Treatment: splinting, steroids, or surgical release.

Incorrect. Carpal tunnel syndrome = median nerve compression. Ulnar nerve passes through Guyon's canal (medial side, outside carpal tunnel). Symptoms are in the lateral 3.5 fingers.

Correct! LOAF = Lumbricals (1st and 2nd), Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (superficial head). These are the thenar and lateral lumbrical muscles supplied by the median nerve in the hand.

LOAF (Median nerve, hand): L1, L2 (lateral lumbricals), Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis. Everything else = ulnar nerve (7 interossei, lumbricals 3&4, hypothenar muscles, adductor pollicis). The ulnar nerve is the 'hand's nerve.'

Incorrect. LOAF = Lumbricals 1&2 (lateral), Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis. All are thenar/lateral hand muscles supplied by the median nerve.

Correct! Ulnar nerve injury causes clawing predominantly in the ring and little fingers (4th and 5th digits) because the ulnar nerve supplies the interossei and lumbricals 3 and 4 which extend the interphalangeal joints of these fingers. Loss of this balanced opposition causes hyperextension at MCP and flexion at IP joints.

Ulnar claw: Primarily ring + little fingers (loss of lumbricals 3&4 and interossei). Hyperextension at MCP + flexion at IP joints. 'Ulnar paradox': lesions at the wrist produce more severe clawing than high (elbow) lesions because FDP for these fingers is also paralyzed in high lesions.

Incorrect. Ulnar nerve injury → ring and little finger claw (4th and 5th digits). The index and middle fingers are supplied by the median nerve (lumbricals 1 and 2).

Correct! The flexor retinaculum attaches medially to the pisiform and the hook of hamate, and laterally to the scaphoid tubercle and trapezium. This creates the carpal tunnel through which the median nerve and flexor tendons pass.

Flexor retinaculum (carpal tunnel roof): Medial — pisiform + hook of hamate. Lateral — scaphoid tubercle + trapezium. Contains: median nerve + 9 tendons (FDS ×4, FDP ×4, FPL ×1). The ulnar nerve and ulnar artery pass superficial to the flexor retinaculum through Guyon's canal.

Incorrect. Flexor retinaculum medial attachments: pisiform + hook of hamate. Lateral: scaphoid tubercle + trapezium.

Correct! The floor of the anatomical snuffbox is formed by the scaphoid (proximally) and the trapezium (distally). The radial artery runs through the floor of the anatomical snuffbox before entering the hand through the first dorsal interosseous muscle.

Anatomical snuffbox: Lateral boundary — APL + EPB tendons. Medial boundary — EPL tendon. Floor — scaphoid + trapezium. Roof — radial artery. Contents: radial artery, cephalic vein (origin), superficial branch of radial nerve. Tenderness here = suspect scaphoid fracture.

Incorrect. Floor of anatomical snuffbox: scaphoid (proximal) + trapezium (distal). The radial artery courses through here.

Correct! The superficial palmar arch is formed primarily by the ulnar artery, completed by the superficial branch of the radial artery (or sometimes the arteria radialis indicis). It lies deep to the palmar aponeurosis and gives off the common palmar digital arteries.

Superficial palmar arch (distal to deep): Primarily ulnar artery + superficial radial branch. Deep palmar arch: Primarily radial artery + deep ulnar branch. The superficial arch is at the level of the fully abducted thumb; the deep arch is 1 cm proximal.

Incorrect. Superficial arch = primarily ulnar artery. Deep arch = primarily radial artery. Mnemonic: 'UR Superficial, RU Deep' (Ulnar-Radial for superficial; Radial-Ulnar for deep).

Correct! Dupuytren's contracture is fibrotic thickening and shortening of the palmar aponeurosis, causing progressive flexion deformity of the fingers (commonly ring > little finger). The nodules and cords in the palm are pathologically thickened bands of the palmar aponeurosis.

Palmar aponeurosis: triangular fibrous sheet in the palm, apex proximal (continuation of palmaris longus tendon), base splits into digital slips. Dupuytren's contracture = fibrotic palmar aponeurosis bands. Risk factors: Northern European ancestry, male, diabetes, alcoholism, manual labor.

Incorrect. Dupuytren's contracture involves fibrosis of the palmar aponeurosis, causing flexion deformity especially of the ring and little fingers. The tendons and muscles themselves are not the primary pathology.

Correct! The deep branch of the radial nerve becomes the posterior interosseous nerve (PIN) as it passes through the Arcade of Frohse, which is the fibrous arch at the proximal edge of the supinator muscle. Compression here causes PIN syndrome (finger drop without wrist drop).

Posterior interosseous nerve (PIN) passes through the supinator via the Arcade of Frohse. PIN syndrome: finger drop (can't extend fingers at MCPs), but wrist extension is preserved (ECRL innervated before the arcade). Compare: radial tunnel syndrome (pain, no paralysis) vs PIN syndrome (motor loss).

Incorrect. The deep radial nerve passes through the Arcade of Frohse (supinator muscle) to become the PIN. PIN syndrome: finger drop, no wrist drop, no sensory loss.

Correct! To isolate FDS in a specific finger, hold all other fingers in full extension (which inactivates the common FDP belly for those digits) and ask the patient to flex the tested finger at the PIP joint. FDS can flex each finger independently; FDP has a common muscle belly that ties the fingers together.

FDS: flexes PIP joint. FDP: flexes DIP joint. To test FDS: isolate by blocking FDP (hold other fingers in extension → FDP tenodesis). To test FDP: hold MCP and PIP extended, ask patient to flex DIP. Clinical: tendon laceration assessment in hand injuries.

Incorrect. FDS is tested by holding other fingers extended (disabling FDP for those digits) and asking for PIP flexion of the tested finger. DIP joint flexion tests FDP.