Nail Anatomy

Overview

• The nail unit includes:
  • Nail plate
  • Surrounding soft tissues
  • Vasculature and innervation related to the distal phalanx
• Key structures:
  • Laminated keratinized nail plate
  • Nail matrix and bed
  • Proximal and lateral nail folds
  • Cuticle (eponychium)
  • Hyponychium at the free edge

Nail Plate

• A modified form of the stratum corneum
• Provides a laminated keratinized structure
• Overlies the nail bed and matrix
• Examined using silver stains, ultrasound, optical coherence tomography, and electron microscopy
• Typically trilaminar but can appear bilaminar

Nail Folds

Lateral Nail Folds

• Provide cushioned cutaneous lateral margins
• More prominent in toes than fingers
• Important for nail adherence to the nail bed
• Issues like onycholysis or ingrown nails can occur if fold size is not compatible with the nail plate size

Proximal Nail Fold (Posterior Nail Fold)

• Originates around week 14 of embryogenesis
• Adherent to the dorsal aspect of the nail plate
• Protects the nail matrix from damage and UV light

Cuticle (Eponychium)

• Epidermal layer extending from the proximal nail fold
• Adheres to the dorsal nail plate
• Loss can indicate chronic paronychia
• Regrowth signifies resolution of inflammation

Nail Matrix and Lunula (Nail Root)

• Divided into matrix (15-25%) and nail bed (75-85%)
• Lunula is the visible part of the distal matrix in some digits
• Important for surgical landmarks and nail excision

Nail Bed (Ventral Matrix, Sterile Matrix)

• Extends from the lunula to the hyponychium
• Features longitudinal epidermal ridges
• Small vessels aligned in the same axis

Onychodermal Band

• Distal nail bed margin with a contrasting hue
• Acts as the first barrier to penetration under the nail plate
• Its state can indicate disease or trauma

Vascular and Nervous System

Arterial Supply

• Radial and ulnar arteries supply the digits
• Forms deep and superficial palmar arcades
• Four arteries per digit with dorsal and palmar digital arteries

Venous Drainage

• Deep and superficial venous systems
• Prominent branching network, especially dorsally

Effects of Altered Vascular Supply

• Impaired supply affects nail unit health
• Linked to conditions like onycholysis and congenital onychodysplasia

Nail Fold Vessels

• Capillary network can be viewed with a dermatoscope
• The venous arm is more dilated than the arterial

Glomus Bodies

• Small cluster of cavernous blood vessels
• Part of arteriovenous anastomosis

Nerve Supply

• Innervation by dorsal branches of paired digital nerves
• Important for anesthesia in nail surgery

Distal Phalanx

• Related to nail unit embryogenesis and lifelong changes
• Nail plate dystrophies linked to phalanx structure

Conclusion

• Understanding the intersection of anatomy, physiology, and disease aids in analyzing nail pathologies
• Essential for planning surgery and therapeutic strategies.