Type IV-D thumb duplication: A new reconstruction method.

INTRODUCTION: In the Wassel type IV classification category, the thumb is duplicated from the metacarpophalangeal joint; this abnormality accounts for approximately 50% of the cases of thumb duplication. Type IV is divided into four subtypes in which the IV-D type, or convergent (9% of cases), is the most complex form because both thumbs are hypoplastic with a divergent metacarpophalangeal joint and a convergent interphalangeal joint. Reconstruction is prone to axis deformity and ligament laxity, whereas the Bilhaut-Cloquet technique's main pitfall is nail dystrophy. We propose a modified Bilhaut-Cloquet procedure to avoid these complications.

MATERIAL AND METHOD: Four males (mean age: 11 months; range: 10-12 months) with IV-D thumb duplication were operated on using a modified Bilhaut-Cloquet procedure.

SURGICAL TECHNIQUE: The skin is preliminarily marked, taking into account the excision of the central skin and the more hypoplastic nail of the two (most often the radial nail). Both proximal phalanges are split longitudinally and the central halves discarded. An oblique osteotomy is performed at the base of the distal phalanx of the ulnar thumb duplicate (the less hypoplastic) and the radial wedge is excised. The same osteotomy is applied to the distal phalanx of the radial thumb duplicate, but the radial wedge is preserved. The proximal phalanx and the bases of the distal phalanx are joined by bone suture. Axis correction and ligament stability are thus achieved without nail surgery.

RESULTS: The patients were examined with a mean 24 months of follow-up (range: 12-36 months). The result was good in all four cases according to the Horii score.

DISCUSSION AND CONCLUSION: This procedure combines an excision of the central part of the proximal phalanx and partial excision of the base of the distal phalanx. It provides axis correction and stabilization of the interphalangeal joint while avoiding subsequent nail dystrophy because a single nail is preserved. Preliminary results are encouraging: no axis deformity, instability or nail dystrophy has been noted. Nonetheless, the long-term results need to be evaluated.

LEVEL OF EVIDENCE: IV retrospective study.