Anatomic Association of the Proximal Fingernail Matrix to the Extensor Pollicis Longus Tendon: A Morphological and Histological Study

Background: Extensor tendon disorders may cause severe functional impairments, and there is a lack of knowledge about their anatomic associations with the proximal fingernail matrix. Objective: To delineate the association between the distal extensor pollicis longus tendon (EPLT) insertion and the limit of the fingernail matrix in the thumb. Methods: The limit of the fingernail matrix and the distal bony insertion of the EPLT were identified in five thumbs from fresh-frozen human cadavers. An additional five thumbs were fixed and the longitudinal thumb sections were histologically analyzed. Results: The terminal limit of the matrix and fingernail was dorsal and overlapped to the EPL tendon, which was located between the fingernail matrix and the phalanx, and extended dorsally to the distal section of the terminal phalanx in all ten thumb bodies. Conclusion: The fingernail matrix is not directly inserted into the periosteum of the dorsal section of the base to the distal phalanx, because this anatomic relationship is separated by the deep fibers of the EPLT.