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:

Ans. b. Posterior interosseous nerve (Ref: Snells 7/e p484 578-580; Keith and Moore 4/e p730, 761)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 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 normal)Loss of metacarpophalyngeal joint extensionRadial Nerve (C5,6,7,8 T1) Posterior cord of Brachial plexusAbove Elbow(High radial nerve palsy)Below Elbow(Low 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