Lateral nail plate impingement on the adjacent nail fold, producing pain, inflammation, and granulation tissue.
Also known as: onychocryptosis, ingrown toenail, unguis incarnatus
Overview
Onychocryptosis is the painful inflammatory condition in which the lateral or distal edge of the nail plate penetrates or pressures the adjacent periungual soft tissue, producing inflammation, granulation tissue, and secondary infection. The hallux is involved in the great majority of cases.
Epidemiology
Most common in adolescents and young adults due to increased perspiration, footwear pressure, and active foot use. Also frequent in older adults with toenail dystrophy and reduced self-care. Diabetic patients are at increased risk for serious complications. Slight male predominance.
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Improper nail trimming (curved or 'rounded' trimming) — most common modifiable factor
Tight, narrow, or ill-fitting footwear
Trauma to the great toe (running, kicking sports)
Hyperhidrosis
Congenital nail-fold or nail-plate shape abnormalities (pincer nails, convoluted toes)
Obesity
Onychomycosis or other nail dystrophy
Oral retinoid therapy (isotretinoin)
Diabetes and peripheral vascular disease (worsen complications, not necessarily incidence)
Pathophysiology
The lateral nail plate, often after misdirected trimming or trauma, presses into or pierces the lateral nail fold. Persistent mechanical pressure and minor breaks in the skin produce inflammation, often followed by bacterial infection (Staphylococcus aureus, mixed flora) and exuberant hypertrophic granulation tissue. Untreated, the condition self-perpetuates because the granulation tissue covers the offending nail edge and prevents spontaneous resolution.
Clinical presentation
Symptoms
Localized pain at the lateral nail fold, exacerbated by footwear or walking
Redness, swelling, and warmth of the affected fold
Purulent or serosanguineous drainage in advanced (Stage II-III) disease
Bleeding from friable granulation tissue
Signs / physical exam
Stage I (inflammation): erythema and mild edema of the nail fold, tenderness with pressure
Stage II (infection): worsened erythema, drainage, hyperhidrosis, beginning granulation
Stage III (chronic): hypertrophic granulation tissue, lateral nail-fold hypertrophy, possible nail plate dystrophy
Typical localization: medial or lateral border of the hallux
Classic findings
Painful, erythematous lateral hallux nail fold with exuberant granulation tissue covering an embedded nail spicule.
Differential diagnosis
Paronychia (acute or chronic) — Inflammation of the proximal/lateral nail fold without nail plate impingement; treat the infection/dermatitis
Pyogenic granuloma of the nail fold — Friable vascular nodule that bleeds easily; may arise on top of chronic ingrown toenail or with retinoid therapy
Subungual exostosis — Bony outgrowth lifting the distal nail; visible on radiograph
Squamous cell carcinoma of the nail unit — Chronic non-healing lesion of the periungual skin; biopsy any persistent unilateral 'ingrown toenail' that does not respond
Partial nail avulsion + phenol matricectomy (definitive)
Heifetz staging of onychocryptosis and stage-directed therapy.
Treatment
First-line
Stage I (mild): warm soaks 10-20 min several times daily; meticulous foot hygiene; loose footwear; trim nails straight across (do NOT round the corners); cotton wisp or dental floss placed under the offending nail edge to lift it off the fold; topical antiseptic (chlorhexidine, povidone-iodine)
Stage I-II with infection: topical mupirocin; oral antibiotics (cephalexin or dicloxacillin; clindamycin or TMP-SMX if MRSA suspected) when cellulitis or systemic signs present
Stage II not responding to conservative care or Stage III: partial nail avulsion (removal of the offending lateral edge of the nail plate) under digital block with 1-2% lidocaine without epinephrine — definitive when combined with matricectomy for recurrent disease
Phenol chemical matricectomy (88% phenol applied to the lateral matrix for 30-60 seconds, repeated) following partial nail avulsion — recurrence rates 1-5% (Cochrane review Eekhof 2012); superior to surgical matricectomy alone
Second-line / adjunct
Sodium hydroxide chemical matricectomy as an alternative to phenol
Surgical matricectomy (Winograd procedure) — definitive but higher recurrence than phenol
Silver nitrate 10-25% application to granulation tissue or topical timolol 0.5% solution for exuberant granulation
Gutter splinting or nail-brace therapy for mild recurrent disease in patients unwilling to undergo avulsion
Evaluate and treat hyperhidrosis (aluminum chloride, glycopyrrolate) and ill-fitting footwear
Complications
Recurrence (10-50% after avulsion alone; 1-5% after avulsion + phenol matricectomy)
Cellulitis, osteomyelitis of the distal phalanx (especially in diabetics)
Pyogenic granuloma of the nail fold
Chronic nail dystrophy and cosmetic deformity
Limb-threatening infection in patients with peripheral vascular disease or diabetic neuropathy
Phenol matricectomy local complications: prolonged drainage, hypopigmentation, narrow nail
PANCE pearls
Trim toenails straight across — never round the corners; this is the most important preventive measure.
Conservative therapy (warm soaks, cotton wisp under the nail edge, proper footwear) cures most Stage I cases.
Antibiotics alone do not cure infected onychocryptosis without addressing the nail edge.
Phenol matricectomy after partial nail avulsion is the most durable cure for recurrent disease — Cochrane evidence supports it.
Diabetic and vasculopathic patients require lower threshold for definitive procedure and tight follow-up; do not let mild disease smolder.
Persistent, non-healing 'ingrown toenail' deserves a biopsy to rule out squamous cell carcinoma or amelanotic melanoma — particularly in adults with no clear mechanical cause.
References
Cochrane 2012 — Eekhof JAH et al. Interventions for ingrowing toenails (Cochrane Database Syst Rev 2012)
AAFP — Mayeaux EJ et al. Ingrown toenail management (American Family Physician 2019)
BMJ Clinical Review — Heidelbaugh JJ, Lee H. Management of the ingrown toenail (Am Fam Physician 2009)
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