Extension Block Kirschner Wire Fixation for Acute Bony Mallet Finger: A Retrospective Analysis

Bony mallet finger is a common injury of the distal phalanx that often requires surgical fixation when fracture displacement disrupts joint congruity. Extension-block Kirschner wire fixation, originally described by Ishiguro, is a minimally invasive method with high reported success rates. This study aimed to evaluate the clinical and radiological outcomes of patients with acute bony mallet finger treated with the extension-block technique using Kirschner wires.

A retrospective review was conducted on 76 patients treated surgically between October 2020 and December 2023. Radiographic union, extension lag, Crawford classification scores, and complications were analysed. Fractures were also categorised according to the Wehbé and Schneider classification. Statistical analyses included the Shapiro-Wilk test, Wilcoxon signed-rank test, and Chi-square or Fisher's exact tests as appropriate.

The mean patient age was 34.4 ± 11.6 years. The median injury-to-surgery interval was 3 days, and the median follow-up duration was 18.5 months. Union was achieved in 97% of cases. The median preoperative DIP joint extension lag improved significantly from 8.8° (IQR 5.8-14.2) to 2.1° (IQR 0-4.8) at final follow-up (p < 0.001, r = 0.72). According to the Crawford classification, 80.2% of patients achieved excellent results, 13.2% good, 1.3% satisfactory, and 5.3% poor outcomes. Complications were limited to two non-unions and one malunion (3.9%).

Extension-block Kirschner wire fixation provides excellent functional and radiographic outcomes in the treatment of acute bony mallet finger when performed early. The technique is safe, effective, and minimally invasive, with low complication rates and high union success.