Wrist drop is due to injury to ?

Clinical features of radial nerve palsyClinical features depend upon the site of lesion.1) If lesion is highWrist drop, thumb drop and finger drop.Inability to extend elbow, wrist, thumb & fingers (MP joint)Patient can extend interphalangeal joints due to action of lumbricals and interossei.Sensory loss over posterior surface of arm & forearm and lower lateral half of forearm.2) If lesion is lowa) Type IWrist drop, thumb drop and finger drop.Elbow extension is preserved.Sensory loss over the dorsum of first web space.b) Type IIThumb drop and finger dropElbow and wrist extension is preservedSensory loss over the dorsum of first web space.