Bilateral congenital absence of the opponens pollicis muscle: a case report

Thumb hypoplasia and thenar muscle anomalies are complex congenital conditions that are associated with other congenital anomalies or syndromes. Congenital absence of the opponens pollicis muscle is very rare and is associated with the absence of other muscles.

A 6-year-old male was referred to our clinic with a provisional diagnosis of carpal tunnel syndrome because electromyography findings at the referring hospital were consistent with this diagnosis. He was unable to oppose his thumbs to his other fingers or grasp objects. All physical examination, electromyography, and magnetic resonance imaging findings were consistent with bilateral absence of the opponens pollicis muscle.

The patient underwent bilateral transfer of the extensor indicis proprius tendon. At 1 year after surgery, he had satisfactory thumb opposition on both sides.

Differentiation between congenital muscle anomalies and carpal tunnel syndrome is very important in order to avoid performing unnecessary surgical procedures. We present a case of bilateral congenital absence of the opponens pollicis muscle, which has not previously been reported, and review the literature regarding congenital muscle anomalies of the hand.