Pollex abductus in hypoplasia and duplication of the thumb.

Pollex abductus is an anomaly in which the flexor pollicis longus attaches not only at its customary insertion, but also into the extensor by a tendon that passes around the radial aspect of the thumb. Contraction of the anomalous flexor abducts the thumb. In the original report, the anomaly occurred in thumb hypoplasia. A similar anomaly is reported in 11 hypoplastic thumbs (35.5% of all cases) and in 9 cases of radial polydactyly (21.4%). The common feature was poor definition of the interphalangeal skin crease, with complete absence of active flexion of that joint. All patients were treated surgically; 13 before the age of 10 months, with correction of the duplication and the hypoplasia, and in the latter with elimination of the abduction deformity and restoration of opposition. The anomalous connection was excised in all patients. Active interphalangeal joint motion after reconstruction of the hypoplastic thumbs averaged 21 degrees.