Anatomic variations in the motor and sensory supply of the thumb.

Variations in the motor and sensory nerve supply to the thumb exist despite stereotyped descriptions in modern anatomy texts. A careful dissection of ten specimens under high magnification has been made with special reference to the nature and incidence of anatomic variations. Transligamentous passage of the recurrent motor branch of the median nerve was noted in six dissections; two of these included multiple motor branches to the thenar musculature. The Riche-Cannieu anastamosis was observed in three specimens. Variations in the branch pattern of the median nerve fibers supplying sensation to the thenar eminance and palmar thumb were also noted. No dorsal (superficial radial nerve) to palmar communications were detected, although this pattern has been described clinically. The differences give rise to an element of diagnostic uncertainty in treating the nerve-injured patient; functional deficits and therapeutic consequences are discussed in relation to the authors' observations and a review of the literature.