Background: Frequently we find atypical tendon insertions when we correct duplicated thumbs. Tendon realignment is mandatory to gain upright position. The insertion of the flexor tendon can be centralized by transposing it ulnarly. But tendon sheath cannot be centralized perfectly. Recurrence of radial tilt at the interphalangeal (IP)-joint level in growth is possible. We want to investigate whether the upright position persists and how often a recurrence can be expected. Patient and Method: We retrospectively analyzed our patients operated from 2000 to 2010 with a minimum follow-up of 3 years postoperation. They are analyzed for sex, age at operation, type of duplication, position, and active and passive range of motion of the IP-joint. Results: Over a period of 11 years, we had operated 28 children with a double thumb showing an atypical flexor tendon insertion which was corrected by tendon transposition: 24 patients came to a follow-up, 3 to 12 years postoperation (mean, 5.2 years). Mostly (n = 16) they suffered by a Wassel IV duplication. Ten patients received a perfect result (straight thumb without deviation), 5 children a light deviation of 10°, and 8 patients developed a clear visible radial deviation of 20° or functional disturbing 30° flexion position of the IP-joint. The malposition developed mainly 5 years postoperation. Four patients of these underwent IP-arthrodesis for secondary correction and 2 are scheduled for this. The IP-joint was always stable and had mostly no, and in some cases up to 40° active mobility. Conclusion: As far as our experience goes, the transposition of the flexor tendon insertion is initially a technique which works for straightening up the IP-joint of a doubled thumb. The impediment in growth occurred mostly around 5 years after the transposition and can be corrected by a straightening IP-arthrodesis.
