Nail – Anatomy

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The ‘nail anatomy’ is very simple and important to understand. Let’s go through it systematically and thoroughly.

Nail Plate

The nail plate comprises of free margin, body and root. The root is ~ 1/4th of the nail plate. On cross-section, divided into dorsal, intermediate (major part) and ventral lamina.

Perionychium

The nail plate sits in an incomplete, invaginated skin pouch on the dorsal aspect of the distal phalanx called perionychium.

Perionychium consists of:

  1. Proximal nail fold (PNF)- consists of Germinal Matrix which is divided into:
    1. Dorsal Roof — or Dorsal matrix – thin ~ 4 layers of keratinocytes- gives rise to dorsal lamina of the nail plate- responsible for the surface shine.
    2. Ventral Floor — or Intermediate Matrix – thick epithelium (> 10 layers of keratinocytes) below lanula (see below) and nail root – gives rise to the most (intermediate lamina) of the nail plate.
  2. Nail bed or Ventral Matrix  (aka – Sterile Matrix) – it gives rise to the ventral lamina of the nail plate that functions as a mold for normal growth of the nail (Hence, any scar on nail bed prevents nail growth over it). It’s very thin- reveals the rich capillary vasculature if the dermis below that separates it from the periosteum of the distal phalanx.

 

nail plate, nail bed, germinal matrix, sterile matrix, paronychium
Nail- Perionychium

 

Nail – Surface anatomy

eponychium, cuticle, lanula
Nail- surface anatomy
  1. Hyponychium – cornified epithelium that adheres to the groove between the free margin of nail plate and the fingertip. It protects the distal edge of the nail bed.
  2. Onychodermal band – the most distal portion of the nail body, lighter pink in color, ? due to the epidermal thickness- hyponychium.
  3. Lanula – pale crescent-shaped area at the proximal part of the nail body, corresponds to the intermediate part of the germinal matrix.
  4. Eponychium – aka Cuticle – formed from epidermis in the distal part of dorsal roof of PNF– adheres to the nail root for protection of the germinal matrix.
Dorsal, intermediate, ventral lamina
Nail plate- germination

Nail growth

  • Rate: 0.1 mm/day
  • After complete removal- takes 4-6 months to grow from PNF to distal edge.
  • Affected by age, season, digit, etc. (more in young age, summer and middle finger)

Functions of Nail

  1. Dorsal cover of distal phalanx.
  2. Magnification of delicate tactile sensations through leverage of the nail plate.
  3. Precise nail-to-nail pinch.
  4. Cosmetic significance.

 

 

Reference:

  1. Atlas of Hand Anatomy and Clinical Implications. By Han-Liang Yu, Robert Chase, and Berish Strauch. Pp. 120-124. Mosby, St. Louis, Mo., 2004

 

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