Radial nerve palsy produces an inability to extend the metacarpophalangeal joints, owing to paralysis of the extensor digitorum communis muscle. However, the lumbrical and interossei muscles, which are served by the median and ulnar nerves and inse into the dorsal expansions (extensor hoods) of the proximal phalanges, are able simultaneously to flex the metacarpophalangeal joints and to extend the interphalangeal joints . Also, abduction of the digits, a function of the dorsal interossei, and adduction, a function of the palmar interossei, are both mediated by the ulnar nerve and, therefore, unaffected .