Only finger drop and no wrist drop in Posterior interosseus nerve injury, is due to sparing of

(D) Extensor carpi radialis longus> Posterior interosseous neuropathy is purely a motor syndrome resulting in finger drop, and radial wrist deviation on extension.# LESIONS OF RADIAL NERVE:> All branches below the injured region will be interrupted.1. Axilla (Very high):> Causes: Glenohumeral dislocation, Fracture proximal humerus, Crutch palsy> Deficit: Total palsy# Triceps weakness: Tested by resisted active extension of elbow and feeling for muscle contraction# Brachioradialis: Tested by resisted active flexion of elbow with forearm in midprone position and feeling for muscle contraction# Wrsit drop: Due to paralysis of wrist extensors- Ask to grasp something, the wrist becomes flexed if extensors are weak# Finger drop: Due to paralysis of long finger extensors causing inability to extend fingers at MCPJ# Thumb drop: Due to paralysis of extensor pollicis longus and abductor pollicis longus- Extensor pollicis longus is examined by stabilizing the MCPJ of thumb and resisted active extension of IP joint of thumb# Sensory loss: Over autonomous zone (1st dorsal webspace)2. Radial groove (High):- Cause: Fracture shaft of humerus, Saturday night palsy, Injection, Callus, Torniquet- Deficit: Brachioradialis weakness, Wrist drop, Finger drop, Thumb drop, Sensory loss3. Below Elbow (Low):- Causes: Fracture of radial head, Posterior dislocation of radius at elbow joint- Deficit: Posterior Interosseous Nerve# No wrist drop (Sparing of Extensor carpi radialis longus which enables extension of wrist)# Finger drop, Thumb drop# No Sensory loss