Pollicization of Biphalangeal Index Finger for Type IV Thumb Hypoplasia: A Case Report Describing Preoperative Planning, Intraoperative Decision-Making, and Technical Modifications

Background: Index finger (IF) pollicization is the standard treatment for severe congenital thumb hypoplasia. The procedure requires a supple and anatomically normal IF. No guidelines exist for IF pollicization in patients who have concomitantly underdeveloped IF, specifically when the digit has only 2 phalanges and 1 interphalangeal joint. Methods: We present a case of a 20-month-old boy with congenital type IV thumb hypoplasia who also had biphalangeal IF. We proposed an IF pollicization operation that required significant modifications to the traditional procedure. Results: Preoperative planning and intraoperative execution are described. The modifications to the traditional procedure included: (1) removal of proximal third of IF metacarpal; (2) creation of a de novo thumb carpometacarpal (CMC) joint by fibrous union whereby the IF CMC joint cartilaginous components are maintained and the remaining distal IF metacarpal is translocated down and secured to this cartilage (in contrast to the traditional use of IF metacarpophalangeal joint as a de novo thumb CMC joint); (3) preservation of IF joints at their “natural” position and function; (4) maintenance of intrinsic muscles at their original distal insertion sites; and (5) important adjustments to skin incision. Conclusions: Pollicization of biphalangeal IF can be executed in a safe and efficient manner. Early recovery has shown promising signs. Long-term results, including the de novo thumb CMC joint function, remain to be evaluated.