Computed tomography based three-dimensional analysis of side-to-side differences between metacarpals.

INTRODUCTION: Metacarpal fractures can cause shortening, rotational, or angular deformities, which may impair function and potentially require surgical correction. CT-assisted preoperative planning frequently references the contralateral metacarpal for alignment purposes. However, there are limited data on the asymmetries between left- and right-hand metacarpals which could influence surgical outcomes.

METHODS: 3D metacarpal bone models were created from CT scans of 20 healthy participants. Each left-hand metacarpal was mirrored and aligned with its corresponding right-hand counterpart. Differences were assessed with respect to pronation/supination, radioulnar deviation, flexion/extension and length.

RESULTS: The mean absolute differences were small but significant, with a mean length difference of 0.6 mm, pronation/supination of 3°, flexion/extension of 1.8° and radial/ulnar deviation of 1.8°. Despite the overall consistency, a small number of outliers were observed for pronation/supination, with differences as high as 10°. The most notable findings among the mean differences were observed in metacarpal pronation/supination, with the left-hand metacarpals being more supinated than the right.

CONCLUSION: There are bilateral asymmetries between the metacarpals, although they are minor and likely to be insignificant in clinical practice. Pronation/supination differences were the most pronounced and should be given particular attention during surgical planning. Surgeons should be aware of these variations and the risk of potential overcorrection or undercorrection.