[The Extensor Pollicis et Indicis: An Accessory or Rudimentary Deep Extensor Tendon to the Thumb? Variants - Frequency - Clinical Relevance].

PURPOSE/

BACKGROUND

Are the supernumerary deep extensor tendons to the thumb in man of accessory or rudimentary origin?

METHOD AND CLINICAL MATERIAL: Two findings of extensor pollicis et indicis (EPI) were classified referring to the literature of comparative anatomy.

RESULTS

Extensor pollicis longus (EPL) and extensor indicis (EI) developed phylogenetically from EPI. A common origin and proximal muscle belly of EPL and EI is a frequent manifestation of incomplete rudimentary EPI. A complete rudimentary EPI with absent EPL and EI has not yet been found in man. The accessory EPI coexisting with EPL and EI occurs in about 2 % of humans.

CONCLUSION

During the EI-tendon transposition to EPL, the tendons must be identified very carefully because of the numerous variants of the deep extensors. Transposition of extensor digitorum communis of the index or just one tendon of a double-tendoned EI to EPL by mistake, will make separate extension of the thumb impossible postoperatively.