Radiographic Characteristics of the Triphalangeal Thumb in Patients With Congenital Thumb Duplication: An Analysis of 383 Thumbs in 368 Children

Purpose The purpose of this study was to evaluate the morphologic and radiographic characteristics of the triphalangeal thumb (TPT) in patients with congenital thumb duplication. Methods We retrospectively reviewed 368 children with TPT duplication (n ¼ 383). Data on age, sex, and laterality were obtained from medical records. The morphologic and radiographic characteristics of the TPT duplication were evaluated using plain radiographs. Results Of the 383 fingers, 322 (84%) had a TPT duplication on the radial side, 36 (10%), on the ulnar side, and 25 (7%) were bilateral. The mean age at the time of surgery of TPT duplication on the radial side (21  11 months), on the ulnar side (25  15 months), and in bilateral cases (27  15 months) was not significantly different. The extra thumb was connected to the main thumb by a joint (75%), bone (18%), soft tissue (6%), and epiphysis (1%). There were 26 cases (7%) of abnormal hypertrophic epiphysis of the main thumb, all of which were located in the distal phalanx of the radial side of the TPT duplications. The thumb epiphyses in patients with TPT duplication appeared in the following order: distal phalanx (mean, 24  14 months; range, 7e94 months), proximal phalanx (mean, 31  18 months; range, 14e94 months), and metacarpal (mean, 34  20 months; range, 13e94 months). Conclusions Triphalangeal thumb in patients with congenital thumb duplication is more common in boys, often duplicated at the level of the proximal phalanx, with the extra thumb articulated to the main thumb by a joint, often unilateral, and frequently radial and right-sided. The epiphysis of the TPT duplication ossifies sequentially from the distal phalanx to the metacarpal, and its onset is delayed in comparison to normal children. (J Hand Surg Am. 2024;-(-):-e-. Copyright  2024 by the American Society for Surgery of the Hand. All rights are reserved, including those for text and data mining, AI training, and similar technologies.) Type of study/level of evidence Diagnostic III.