The radial nerve divides into superficial (sensory) and deep (motor — posterior interosseous nerve) branches at the anterior surface of the lateral epicondyle, just distal to the radiocapitellar joint. This division point is the key landmark separating radial nerve palsy from PIN palsy.
The division of the radial nerve into superficial and deep branches at the lateral epicondyle is the anatomical basis for the clinical distinction between radial nerve palsy (above division — all branches affected) and posterior interosseous nerve palsy (deep branch only — intrinsic hand extensors affected with radial wrist extension preserved). EMG of the ECRL versus EDC distinguishes the two patterns.
Injury at the exact radial nerve division point producing variable sensory and motor deficits depending on whether both or only one division is affected, requiring careful EMG mapping to determine which branches are intact.
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