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Proximal nail fold

The proximal nail fold of the toe is a skin fold that covers and protects the emerging nail plate at its root. It represents the dorsal continuation of the periungual skin, curving over the proximal end of the nail plate and forming a tight seal between the nail and surrounding tissue. The epidermal extension of the fold, known as the eponychium (cuticle), adheres to the nail plate and prevents external contaminants and microorganisms from entering the nail matrix.

This structure is vital for nail growth, protection of the matrix, and maintenance of the nail apparatus integrity. Pathological involvement of the proximal nail fold is seen in paronychia, trauma, psoriasis, and ingrown nail conditions.

Synonyms

  • Eponychial fold

  • Proximal periungual fold

  • Nail root fold

Location and Structure

  • The proximal nail fold is located at the dorsal base of the nail plate, curving over the proximal nail root.

  • Composed of epidermis and dermis, with a thick keratinized surface externally and a thin, non-keratinized epithelium lining the inner surface facing the nail.

  • The eponychium (cuticle) forms from the stratum corneum of the dorsal fold, extending over the nail plate.

  • Beneath the fold lies the germinal matrix, responsible for generating the nail plate.

  • The fold merges laterally with the lateral nail folds and distally transitions into the nail plate.

Relations

  • Superficially: Skin of the dorsal toe and overlying epidermis

  • Deeply: Germinal nail matrix and proximal nail bed

  • Laterally: Lateral nail folds

  • Distally: Nail plate emerging from beneath the fold

  • Proximally: Continuity with dorsal digital skin

Attachments

  • The inner surface of the proximal nail fold adheres to the nail plate via the cuticle (eponychium).

  • Collagen fibers and dermal connective tissue attach it to the periosteum of the distal phalanx through subcutaneous tissue.

  • Continuous with epidermis and dermis of the dorsal toe skin.

Nerve Supply

  • Supplied by digital branches of the plantar and dorsal digital nerves, providing tactile and nociceptive sensation.

  • Rich sensory innervation contributes to high sensitivity of the nail margin.

Function

  • Protection: Shields the nail root and matrix from trauma and infection.

  • Barrier: The eponychium forms a watertight seal preventing microbial ingress.

  • Support: Stabilizes the emerging nail plate during growth.

  • Sensory role: Provides feedback and protection for distal toe tip.

  • Aesthetic and structural integrity: Maintains smooth contour and appearance of nail apparatus.

Clinical Significance

  • Paronychia: Infection of the nail fold (acute or chronic), often due to Staphylococcus or Candida species.

  • Ingrown toenail (onychocryptosis): Pressure from nail edge into adjacent fold causes inflammation and pain.

  • Trauma: Laceration or avulsion may expose the matrix, leading to nail dystrophy.

  • Inflammatory disorders: Psoriasis, lichen planus, and eczema can involve the proximal nail fold.

  • Tumors: Glomus tumor or subungual melanoma may extend under or distort the fold.

  • Surgical relevance: Essential landmark in procedures like nail avulsion, biopsy, or matrix repair.

MRI Appearance

  • T1-weighted images:

    • Epidermis and dermis: Low-to-intermediate signal intensity

    • Subcutaneous fat: Bright signal

    • Nail plate: Low signal linear structure beneath the fold

    • Marrow of distal phalanx: Bright fatty signal (posterior to fold)

    • Pathology: Abscess or granulation tissue appears intermediate-to-bright, replacing normal low-signal fat planes

  • T2-weighted images:

    • Nail fold tissue: Intermediate signal intensity

    • Nail plate: Low signal (dark band)

    • Subcutaneous fat: Intermediate-to-bright

    • Fluid or infection: Bright hyperintense collection beneath or around the fold

    • Edema or cellulitis: Diffuse bright signal with indistinct dermal margins

  • STIR:

    • Normal fold: Intermediate-to-dark signal

    • Inflamed or infected tissue: Bright hyperintensity, highlighting edema or abscess formation

    • Useful for early soft-tissue inflammation and cellulitis detection

  • Proton Density Fat-Saturated (PD FS):

    • Normal tissue: Intermediate-to-dark signal

    • Pathologic: Bright focal or diffuse hyperintensity in edema, infection, or trauma

    • Clearly defines abscess cavities, inflammatory changes, or post-surgical alterations

  • T1 Fat-Sat Post-Contrast:

    • Normal fold: Mild uniform enhancement of dermis

    • Paronychia or cellulitis: Diffuse or rim enhancement around fluid collection

    • Granulation tissue: Homogeneous enhancement; abscess center remains non-enhancing

    • Tumors: Show nodular or irregular enhancement under or around the nail fold

CT Appearance

Non-Contrast CT:

  • Nail plate: Dense linear structure under the fold

  • Skin and subcutaneous tissue: Homogeneous soft-tissue density

  • Pathology:

    • Soft-tissue swelling or asymmetry around fold indicates inflammation

    • Calcification or gas may indicate infection or trauma

    • Bony erosion of distal phalanx visible in chronic infection or tumor invasion

Post-Contrast CT (standard):

  • Normal fold: Mild homogeneous enhancement of dermal tissues

  • Infection: Intense peripheral enhancement around fluid or abscess

  • Tumor or granulomatous lesions: Nodular or irregular soft-tissue enhancement

  • Useful in: Detecting paronychia, osteomyelitis extension, neoplasms, and post-surgical evaluation

MRI image

Proximal nail fold of toe axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Proximal nail fold of toe sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Proximal nail fold ct sag