THE MIRROR HAND ABNORMALITY

A case o f mirror hand in which there were four supernumerary fingers but in which the lateral forearm bone exhibited many o f the features o f a radius is described. Observation showed that, in this case, the supernumary index finger was the most suitable for thumb construction. Rotation osteotomy of the metacarpal o f this finger combined with opposition tendon transfer resulted in the creation o f an efficient, opposable thumb, but transfer o f a finger, extensor tendon to the dorsum of the wrist did not produce lasting benefit. Mirror hand is a rare, unilateral, congenital abnormality in which three or more supernumerary fingers are formed on the radial side of the fingers of the normal hand. It is associated with absence of the thumb, with a flexion deformity of the wrist and with deficiency of the extensor muscles of the wrist. Because both forearm bones normally resemble ulnae, the abnormality has also been classified as ulnar dimelia (Harrison 1960). Surgical treatment of mirror hand involves correction of the flexion deformity of the wrist, construction of a thumb from one or more of the supernumerary fingers and resection of the remaining supernumerary fingers. Construction of a thumb presents a number of problems, and variety of approaches to dealing wit