Snapshot A 12-year-old boy is brought to the emergency department by his mom because he has noticed that he is no longer able to fully extend the fingers of his right hand. Three weeks prior to presentation, he had suffered a right fibula fracture while riding his bike and was given a pair of crutches to use while his leg recovered. He says that he lost that set of crutches and therefore has been using his taller friend's crutches. Upon further questioning he reveals that the new crutches have been putting a lot of pressure on his axilla. On physical exam he is found to have a wrist drop and decreased sensation over his posterior forearm and dorsal hand. (Radial nerve palsy, also known as Saturday night palsy) Overview Axillary Nerve (C5 and C6) Cause of injury fractured surgical neck of humerus dislocation of humeral head Motor deficit arm abduction at shoulder Sensory deficit over deltoid muscle Sign flattened deltoid Radial Nerve (C5-T1) Overview also known as "great extensor nerve" innervates "BEST" Brachioradialis Extensors of wrist, fingers Supinator Triceps Cause of injury fracture at midshaft of humerus "Saturday night palsy" extended compression of axilla by back of chair or crutches Motor deficit wrist extension finger extension at MCP joints supination thumb extension and abduction Sensory deficit posterior arm dorsal hand dorsal thumb Sign wrist drop Median Nerve (C6-C8 and T1) Cause of injury proximal lesion fracture of supracondylar humerus distal lesion carpal tunnel syndrome dislocated lunate Motor deficit proximal lesion oppositon of thumb lateral finger flexion wrist flexion distal lesion wrist flexion Sensory deficit proximal lesion palmar aspects of lateral 3 1/2 fingers dorsal lateral 3 1/2 fingertips thenar eminence distal lesion dorsal and palmar aspects of lateral 3 1/2 fingers Sign distal lesion median claw hand (when asked to extend fingers) due to loss of lateral lumbricals proximal lesion ulnar claw hand (when asked to flex fingers) due to loss of long forearm flexors "Pope's blessing / hand of benediction" Ulnar Nerve (C8 and T1) Cause of injury proximal lesion fracture of medial epicondyle of humerus distal lesion fracture of hook of hamate (falling onto outstretched hand) Motor deficit proximal lesion medial finger flexion wrist flexion distal lesion abduction and adduction of fingers (interossei) adduction of thumb extension of 4th and 5th fingers (lumbricals) Sensory deficit medial 1 1/2 fingers hypothenar eminence Sign distal lesion ulnar claw hand (when asked to extend fingers) due to loss of medial lumbricals proximal lesion median claw hand (when asked to flex fingers) due to loss of long forearm flexors Musculocutaneous Nerve (C5-C7) Cause of injury upper trunk of brachial plexus compression Motor deficit flexion of arm at elbow Sensory deficit lateral forearm