Objective To explore the efficacy of index finger pollicization with Kirschner wire-assisted transposition positioning in the treatment of severe thumb hypoplasia. Methods A retrospective analysis was conducted from April 2024 to March 2026 involving 10 children with severe thumb hypoplasia （Manske modified Blauth type ⅢB-Ⅴ） treated with index finger pollicization using Kirschner wire-assisted transposition positioning. The average age of the patients was 6 years and 5 months （1 year to 13 years and 1 month）， including 6 males and 4 females， with an equal distribution between the right and left hand. There were 5 cases of Blauth ⅢB type，3 cases of Ⅳ type， and 2 cases of Ⅴ type. Postoperative follow-up involved evaluation of appearance and function， measurement of palmar and radial abduction angles of the thumb， the range of motion at the interphalangeal and metacarpophalangeal joints， and two-point discrimination on the thumb pulp. The overall functional outcome of the thumb was assessed using the Kapandji score and Jebsen Hand Function Test， while observing for surgical complications. Results The mean follow-up period was approximately 18.1 months （12 months to 23 months）， with reconstructed thumbs showing an average radial abduction of 50.3 ° and palmar abduction of 70.6 °. The mean flexion of the  metacarpophalangeal joint was 54.2 °， with extension at 1.9 °， while the interphalangeal joint showed mean flexion at 81.8 ° and extension at 1.3 °. The average two-point discrimination on the thumb pulp was 5.6 mm， the average Kapandji score was 7.7 points， and the average total time for the Jebsen test was 412.3 seconds. In this group， there was one patient who developed a hematoma in the palmar region after surgery， leading to superficial necrosis. No other cases showed wound infection or vascular complications. Conclusion Index finger pollicization is a classic surgical approach for treating severe thumb hypoplasia types ⅢB-Ⅴ. This study introduces a novel intraoperative geometric reference based on K-wire alignment with the proximal phalanx， enabling objective and reproducible control of index finger rotation during transposition. Additionally， as the Kirschner wires do not fix the interphalangeal joints across the joint， it facilitates early postoperative interphalangeal joint functional exercises， thereby improving thumb movement function and overall appearance.

Index finger pollicization, Severe thumb hypoplasia, Modified Blauth classification, Kirschner wire assisted transposition localization