Topics

Topic

design image
Lateral nail fold (toe)

The lateral nail fold is the skin and soft-tissue ridge located along the lateral border of the toenail plate. It forms part of the periungual structures that frame and protect the nail unit. The lateral nail fold acts as a protective barrier, shielding the nail matrix and bed from trauma and infection while guiding nail growth.

It consists of epidermis, dermis, subcutaneous connective tissue, and dense fibrous bands that anchor the fold to the distal phalanx and lateral nail bed. Clinically, it is a common site for ingrown toenails (onychocryptosis) and paronychia, where infection or inflammation affects the periungual tissues.

Synonyms

  • Lateral periungual fold

  • Lateral nail margin

  • Lateral paronychium

Location and Structure

  • The lateral nail fold forms the raised ridge of skin on each side of the nail plate.

  • Composition: Stratified squamous keratinized epithelium, underlying dermis, and subcutaneous connective tissue.

  • Attachment: Firmly adherent to the periosteum of the distal phalanx by fibrous septa.

  • Relation to nail plate: Overlaps the lateral edge, forming a narrow groove — the lateral nail sulcus.

  • Continuity: Proximally continuous with the proximal nail fold and distally blending into the hyponychium.

Relations

  • Medially: Nail plate and nail bed

  • Laterally: Dorsal skin of toe tip

  • Deep (internal): Periosteum and distal phalanx

  • Superficially: Keratinized epidermis and dermis forming protective barrier

  • Distally: Hyponychium and tip of toe

Attachments

  • Fibrous septa: Connect the fold to the periosteum of the distal phalanx, stabilizing the lateral nail margin

  • Epidermis: Continuous with the nail wall and dorsal skin

  • Dermis: Contains vascular and neural plexuses supplying the periungual region

  • Subcutaneous tissue: Houses small fat lobules and connective tissue supporting the nail fold structure

Nerve Supply

  • Digital branches of the medial and lateral plantar nerves (from tibial nerve) supply the plantar aspect

  • Dorsal digital nerves (from deep fibular or superficial peroneal nerves) supply the dorsal nail fold and margin

Function

  • Protection: Shields the lateral nail bed and matrix from trauma, moisture, and pathogens

  • Nail guidance: Directs longitudinal growth of the nail plate within the lateral sulcus

  • Barrier maintenance: Prevents debris and fluid infiltration into the nail bed

  • Sensory role: Richly innervated for tactile sensation, important in pressure perception at toe tip

  • Structural stability: Anchors nail plate laterally and supports even nail curvature

Clinical Significance

  • Ingrown toenail (onychocryptosis): Common at the lateral nail fold due to improper trimming, tight footwear, or trauma

  • Paronychia: Bacterial or fungal infection causing swelling, redness, and abscess formation

  • Granulation tissue formation: Occurs in chronic irritation or infection

  • Nail fold hypertrophy: Thickening from repeated trauma or chronic inflammation

  • Tumors or cysts: Glomus tumors, epidermoid cysts, or subungual exostoses may involve the periungual fold

  • Imaging importance: MRI and CT identify inflammation, abscesses, or osseous involvement beneath nail fold pathology

MRI Appearance

  • T1-weighted images:

    • Skin and subcutaneous tissue: Intermediate signal

    • Fat: Bright signal outlining fold and subcutaneous layers

    • Nail plate: Low signal (dark linear band)

    • Bone cortex of distal phalanx: Low signal; marrow bright on T1

    • Infection or inflammation: Appears as ill-defined low-to-intermediate signal with soft-tissue thickening

  • T2-weighted images:

    • Normal tissue: Intermediate-to-low signal intensity in soft tissue and nail plate

    • Fat: Bright signal

    • Inflammation or abscess: Bright hyperintense signal within soft tissue with surrounding edema

    • Nail plate: Low signal band; subungual fluid collections appear hyperintense

  • STIR:

    • Normal lateral nail fold: Intermediate-to-dark signal

    • Infected or inflamed fold: Bright hyperintense signal representing edema and cellulitis

    • Abscesses: Well-defined bright collection with dark capsule-like margin

  • Proton Density Fat-Saturated (PD FS):

    • Normal tissue: Intermediate-to-dark with well-defined layers

    • Inflammation or infection: Bright signal in soft tissue, especially in paronychia

    • Useful for: Detecting subtle abscesses, sinus tracts, or cellulitic spread

  • T1 Fat-Sat Post-Contrast:

    • Normal: Minimal enhancement of dermal vascular plexus

    • Infection/inflammation: Diffuse or ring-like enhancement around abscess cavity

    • Chronic granulation tissue: Heterogeneous enhancement with low-signal fibrotic strands

    • Osteomyelitis: Marrow enhancement of adjacent distal phalanx if infection extends deep

CT Appearance

Non-Contrast CT:

  • Soft tissue: Homogeneous low attenuation surrounding nail plate

  • Nail plate: Thin hyperdense keratinized structure overlying distal phalanx

  • Inflammation: Soft-tissue swelling, obliteration of subcutaneous fat planes

  • Abscess: Low-density fluid collection with rim definition

  • Bone changes: Detects cortical erosions, periosteal reaction, or subungual exostosis

Post-Contrast CT (standard):

  • Inflamed tissue: Enhancing soft-tissue thickening

  • Abscess: Peripheral rim enhancement with central low attenuation

  • Bone involvement: Enhanced periosteum or cortical irregularity suggests osteomyelitis

  • Excellent for: Differentiating cellulitis, abscess, or bone infection in chronic nail fold disease

MRI image

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

MRI image

Lateral nail fold of toe coronalcross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Lateral nail fold ct axial image