The Snow-Fink Technique as an Opposition Tendon Transfer for Children Born with a Hypoplastic or Absent Thumb

Abstract

Background

A novel opposition tendon transfer, previously described by Snow and Fink in adults but not in children, can provide better functional results and cosmetic appearance than the currently preferred Huber transfer.

Methods

Thirty-one children were born either without a thumb (17) or with a hypoplastic thumb (14). Thirty-eight thumbs were classified according to the Blauth classification as stages II, IIIA, IIIB, IV, and V respectively. The opposition tendon transfer was performed between the ages of 4 and 10, using the expendable flexor digitorum superficialis (FDS) tendon from the ring finger which was passed through a 3-mm-diameter window in the transverse carpal ligament, routed subcutaneously across the palm and attached to the insertion of the abductor pollicis brevis on the base of the proximal phalanx of the thumb. This creates a vector of pull from the ulnar side of the hand which both abducts and pronates the thumb. Twenty-one hands underwent additional procedures such as four-flap Z-plasty (11), ulnar collateral ligament reconstruction (6), joint transfer, full-thickness skin grafting, and distraction lengthening.

Results

The ability of each child to oppose their thumb to the index finger (score 2), middle finger (score 3), ring finger (score 4), or small finger (score 5) was assessed preoperatively and postoperatively by their Kapandji score. Thirty-one children (81.6 %) achieved a postoperative Kapandji score of 5, while 7 children (18.4 %) had a postoperative Kapandji score of 4. No deformities were observed, and the metacarpophalangeal (MCP) joint was stabilized with the other slip of the FDS when necessary.

Conclusions

An opposition transfer using the FDS tendon of the ring finger through a window in the transverse carpal ligament is a simple and reliable technique for improving thumb function in children born with an absent or hypoplastic thumb. This transfer does not produce a concave deformity in the hypothenar eminence like the Huber transfer, provides better pronation, and affords concurrent stabilization of the MCP joint.