The opponens pollicis tendon inserts along the entire radial first metacarpal border, allowing it to rotate, flex, and abduct the metacarpal simultaneously to produce true thumb opposition — the movement unique to humans that places the thumb pulp opposite the finger pulps. Its thenar eminence bulk forms the medial thenar mound and its wasting in median nerve palsy produces the characteristic flat thenar eminence of carpal tunnel syndrome.
Thumb opposition by rotating and flexing the first metacarpal across the palm
Opponens pollicis atrophy produces the flat thenar eminence and simian hand deformity of chronic high median nerve palsy, with loss of thumb opposition that significantly impairs all pinch and grip activities. Thumb opposition reconstruction using the flexor digitorum superficialis (Bunnell), extensor indicis (Brand), or abductor digiti minimi (Huber) tendon transfers restores functional opposition.
Opponens pollicis and thenar muscle atrophy from chronic median nerve compression producing flat thenar eminence and thumb opposition weakness, managed with carpal tunnel release before irreversible muscle loss.
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