[Technical note: ulnar "pseudo-pollicisation" in congenital hand differences].

In certain rare cases of thumb aplasia or hypoplasia, pollicisation of the second finger is not recommended or impossible. It happens when the most radial fingers are hypoplastic or abnormal or when an ulnar prehension pattern has already developed. In these cases, if functional, pollicisation of the most ulnar finger in not suitable because of the ugly cosmetic result. In order to combine the functional advantages of the ulnar pollicisation with a satisfactory cosmetic appearance, the authors describe pseudo-ulnar pollicisation by supination osteotomy. This operation combines rotation of the fifth ray with the establishment of a larger web space between the two most ulnar fingers. We have used this technique in five preliminary cases with a minimum follow-up of 18 months.