wrist drop

Wrist drop results from paralysis of the wrist and finger extensor muscles (extensor carpi radialis longus/brevis, extensor carpi ulnaris, extensor digitorum), which are innervated by the radial nerve (C5-T1). The radial nerve runs in the spiral (radial) groove of the humerus, making it vulnerable to injury from midshaft humeral fractures, prolonged compression (e.g., 'Saturday night palsy' from sleeping with arm draped over a chair, or crutch use), or improperly fitted tourniquets. Lead poisoning can also cause wrist drop (often bilateral) due to peripheral neuropathy affecting the radial nerve preferentially, along with other findings like microcytic anemia with basophilic stippling and abdominal colic. Clinical presentation includes weakness of wrist and finger extension, with the hand falling into flexion when the arm is extended; there may also be sensory loss over the dorsal hand/forearm (posterior/dorsal aspect), particularly the dorsal web space between thumb and index finger. Reflexes affected include diminished brachioradialis reflex. Differentiate from other causes of hand weakness: ulnar nerve injury causes claw hand, median nerve injury causes ape hand or benediction sign (depending on level), and C7 radiculopathy can mimic radial neuropathy but typically also affects triceps reflex and has more widespread motor/sensory findings. Management includes treating the underlying cause, physical therapy, and splinting to prevent contractures; most cases from transient compression resolve spontaneously over weeks to months as the nerve recovers.