Anomalous extensor muscles of the hand: a review.

Anomalous extensor muscles of the hand are not uncommon. Well-recognized anomalies anomalous extensor indicis proprius, extensor digitorum brevis manus, extensor medii proprius, and extensor indicis et medii communis are reviewed and discussed in detail. Anomalous extensor indicis proprius and extensor digitorum brevis manus may occasionally give rise to dorsal wrist pain and the diagnosis is often confused especially in the presence of other pathologic findings such as a ganglion. An analysis of the embryologic development of the extensor muscle mass with phylogenetic comparisons between species of the animal kingdom is presented to underscore the clinical relevance of these anomalous extensors.