median nerve palsy

**Anatomy:** The median nerve arises from the lateral cord (C5–C7) and medial cord (C8–T1) of the brachial plexus. In the forearm it supplies the pronator teres, FCR, palmaris longus, and FDS. Its anterior interosseous branch supplies FDP (digits 2–3), FPL, and pronator quadratus. In the hand it supplies the LOAF muscles (Lateral 2 lumbricals, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis, superficial head). Sensory: palmar surface of the lateral 3½ digits and the thenar eminence/lateral palm (via the palmar cutaneous branch, which passes superficial to the carpal tunnel), plus the dorsal fingertips and nail beds of digits 2–3 and the radial half of digit 4.

**Common sites of injury and clinical findings:** 1. **Carpal tunnel (wrist), the most common site:** Carpal tunnel syndrome. Causes include repetitive use, pregnancy, hypothyroidism, diabetes, rheumatoid arthritis, acromegaly, amyloidosis, obesity, and wrist fracture. Findings are paresthesias and pain in the lateral 3½ digits, often worse at night, with relief from shaking the hand ("flick sign"). Later there is thenar atrophy and weak thumb abduction/opposition. The **thenar eminence sensation is spared** because the palmar cutaneous branch arises proximal to the tunnel. Tests are Tinel sign (percussion over the nerve), Phalen sign (wrist flexion), and the carpal compression test. Nerve conduction studies/EMG confirm it. Treatment is a wrist splint in neutral position, steroid injection, then surgical release of the transverse carpal ligament. 2. **Elbow/proximal forearm:** Supracondylar humerus fracture (especially in children), pronator teres syndrome, or ligament of Struthers entrapment. Findings include weak forearm pronation, weak wrist flexion with ulnar deviation (FCR lost, FCU intact), and the "hand of benediction" (index and middle fingers cannot flex when making a fist; ring and little fingers flex via ulnar-innervated FDP) plus all distal deficits. 3. **Anterior interosseous nerve syndrome (pure motor):** Seen after supracondylar fracture or forearm compression. The patient can't make an "OK" sign (weak FDP to digits 2–3 and FPL), and shows a positive "pinch" sign with tip-to-tip pinch (pulp-to-pulp) replaced by a pinch of the pad. There is no sensory loss. 4. **Pronator teres syndrome:** Compression between the two heads of pronator teres. It causes forearm pain and sensory symptoms, including the palmar cutaneous distribution (so thenar sensation is lost, unlike in CTS). Symptoms worsen with repetitive pronation. 5. **Lacerations at the wrist:** Cause thenar weakness and sensory loss in the median distribution.

**Key signs:** - **Ape hand:** Thenar atrophy with a thumb that is adducted and in the same plane as the fingers, from loss of opposition and abduction. - **Hand of benediction (pope's blessing):** Seen with proximal lesions when the patient attempts to make a fist. - Weak thumb opposition, so the patient can't touch the thumb to the 5th digit. - Weak lateral lumbricals, so the patient can't flex the MCP and extend the IP of digits 2–3.

**High-yield comparisons:** - **Ulnar nerve:** Claw hand (distal lesion), Froment sign, loss of finger abduction/adduction, hypothenar atrophy. Don't confuse its "ulnar claw" with the median "hand of benediction." The ulnar claw is most prominent with a *distal* lesion, and the benediction sign is seen with *proximal* median lesions when making a fist. - **Radial nerve:** Wrist drop (Saturday night palsy, humeral shaft fracture). - Carpal tunnel contents: median nerve plus 9 tendons (4 FDS, 4 FDP, FPL). The ulnar nerve and artery pass through Guyon's canal, not the carpal tunnel.

**Management:** Treat the underlying cause, splint, steroid injection, and surgical decompression for refractory or progressive cases. Traumatic transections require surgical repair. Proximal lesions need elbow/forearm exploration or fracture management.