Histology of the volar plate of the thumb metacarpophalangeal joint

Background: The aim of the study was to describe the histology of the thumb MCPJ volar plate. Methods: Five fresh-frozen thumbs were dissected. The volar plates were harvested from the thumb MCPJ. Histological analyses were performed using 0.04% Toluidine blue and counterstained with 0.005% Fast green. Results: The thumb MCPJ volar plate comprised two sesamoids, dense fibrous tissue and loose connective tissue. The two sesamoids were connected by dense fibrous tissue, with collagen fibers oriented transversely (perpendicular to the long axis of the thumb). In contrast, the collagen fibers within the dense fibrous tissue on the lateral sides of the sesamoid were oriented longitudinally in line with long axis of the thumb. These fibers blended with the fibers of the radial and ulnar collateral ligaments. The collagen fibers in the dense fibrous tissue distal to the sesamoids ran transversely, perpendicular to the long axis of the thumb. The proximal aspect of the volar plate showed only loose connective tissue. The volar plate of the thumb MCPJ was largely uniform with no division of layers from the dorsum to the palmar surface. There was no fibrocartilaginous component in the thumb MCPJ volar plate. Conclusions: The histology of the volar plate of the thumb MCPJ differs significantly from the conventional understanding of the volar plate, based on the volar plate of finger proximal interphalangeal joints. The difference is likely due to the presence of the sesamoids, which confer additional stability, reducing the need for a specialized trilaminar fibrocartilaginous structure with the lateral check-rein ligaments found in the volar plate of finger proximal interphalangeal joints to confer additional stability. (C) 2023 SFCM. Published by Elsevier Masson SAS. All rights reserved.