<prompt> A patient woke up with difficulty in extending fingers, can make a grip and hold a pen. Dorsiflexon was normal. Sensory and motor examination was normal. Nerve most commonly involved:C8T1Posterior interosseous nerveLower brachial plexusHand area in cortex  <response>: Ans. b. Posterior interosseous nerve Ref: Snells 7e p484 578-580; Keith and Moore 4e p730, 761A patient woke up with difficulty in extending fingers, can make a grip and hold a pen. Dorsiflexon was normal. Sensory and motor examination was normal. Nerve most commonly involved is Posterior interosseous nerve.Posterior Interosseous Nerve Palsy:Nerve supplying extensors: Lesion can lead to difficulty in extending fingersElbow, wrist, interphalangeal joint extension and sensations are spared can make a grip and hold a pen. Dorsiflexon was normal. Sensory and motor examination was normalLoss of metacarpophalyngeal joint extensionRadial Nerve C5,6,7,8 T1 Posterior cord of Brachial plexusAbove ElbowHigh radial nerve palsyBelow ElbowLow radial nerve palsy Above spiral groove:- TricepsQ Long, medial head- Posterior cutaneous nerve of arm In spiral groove:- Posterior cutaneous nerve of forearm- Lateral cutaneous nerve of arm- Triceps Medial and lateral head in upper part of spiral groove- AnconeusQ in lower part of groove Between spiral groove and lateral epicondyle:- BrachialisQ- BrachioradialisQ- Extensor carpi radilais longusQ Posterior interosseous nerve supply remaining muscle:- Abductor pollicis longus- Extensor pollicis longus and brevis- Extensor indices- Supinator- Extensor digitorumQ- Extensor digitiQ minimi- Extensor carpi ulnaris- Extensor carpi radilis brevisQ Superficial radial nerve supplying dorsal aspect of 1st web spaceQ autonomous zone Type of Radial Nerve LesionVery high above spiral groove: Total palsyElbow, wrist, thumb and finger extension is lostLoss of sensationHigh Between spiral groove and lateral epicondyle:Elbow extension sparedQLost: Wrist, thumb, finger extension and sensationLow Below elbow:Elbow and wrist extension sparedQLost: Thumb, finger extension and sensationPosterior interosseous nerve palsy:Elbow, wrist, interphalangeal joint extension and sensations are sparedQLoss of metacarpophalyngeal joint extensionQ 