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

Abstract

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.

Keywords: extensor pollicis longus tendon; nail bed; nail deformity; nail matrix.

Figure 1

Exposing the nail matrix, the distal interphalangeal joint, and the terminal extensor pollicis longus tendon.

Figure 2

Exposing the distal insertion of the extensor pollicis longus tendon at the base of distal phalanx to the point of the proximal nail matrix fold. (A) The tendon attached to the dorsal aspect of the base of the distal phalanx from the distal interphalangeal joint line to the tendon reaching the proximal nail fold matrix. (B) The tendon at the middle aspect of the distal phalanx in the same specimen. (C) The tendon reaching the distal aspect of the distal phalanx.

Figure 3

Drawing corresponding to Figure 4: (1) epidermis; (2) hyponychial phalangeal (anterior) ligament; (3) hyponychium; (4) nail plate; (5) nail matrix; (6) the superficial extensor pollicis longus (EPL) tendon bundle to the distal phalanx of the thumb aponeurotic expansion; (7) cuticle (8) superficial EPL tendon bundle that continues to the distal phalanx of the thumb; (9) superficial fibers of the EPL bundles. DF—distal phalanx; EPL—extensor pollicis longus; IFJ—interphalangeal joint; PF—proximal phalanx.

Figure 4

Sagital section of the thumb. The superficial fibers of the EPL tendon bundles extend to the dorsal aspect of the distal phalanx of the thumb (arrowheads). Convex and concave structures form the interphalangeal joint of thumb. The red and green squared areas correspond to Figure 5 and Figure 6, respectively. NP—nail plate; DF—distal phalanx. (5× magnification). Tetrachrome VOF-III GS stain (light green SF/or fast green FCF, methyl blue, Orange G, and acid fuchsin).

Figure 5

High-power magnification of the red squared area of Figure 4. The superficial EPL tendon bundle attached to the distal phalanx of the thumb (arrowheads). NP—nail plate; DF—distal phalanx. (10× magnification). Tetrachrome VOF-III GS stain (light green SF/or fast green FCF, methyl blue, Orange G, and acid fuchsin).

Figure 6

High-power magnification of the green squared area of Figure 4. Deep fibers of the extensor pollicis longus tendon (EPLT) bundles run along the dorsal aspect of the distal phalanx of the thumb (arrowheads). Superficial fibers of the EPL (arrow) are attached at the base of the ventral nail matrix (asterisk) and to the underlying bone crossing the superficial fibers of the EPLT bundles (10× magnification). Tetrachrome VOF-III GS stain (light green SF/or fast green FCF, methyl blue, Orange G, and acid fuchsin).

Figure 7

High-power magnification of the yellow squared area of Figure 6. Detail of the superficial fibers of the EPL bundles (blue and red arrows) attached at the base of ventral matrix (asterisk) to the underlying distal phalanx (DF) bone, crossing the deep fibers of the extensor pollicis longus tendon (EPLT) bundles (green arrowheads). Superficial fibers of the EPL tendon expansion to the eponychium (blue and red arrow), which run distally along the complete dorsal aspect of the distal phalanx, until its end (20× magnification). Tetrachrome VOF-III GS stain (light green SF/or fast green FCF, methyl blue, Orange G, and acid fuchsin).