Ingrown Toenails

Etiology

Improper nail trimming and inadequate foot hygiene represent the most common etiologic factors in the development of ingrown toenails, as they may result in the formation of a nail spicule that penetrates adjacent periungual soft tissue, predisposing to localized inflammation and secondary bacterial infection.[2][3] Other predisposing factors for ingrown toenails include tight-fitting shoes, hyperhidrosis, trauma, digital deformities, eg, hallux valgus (also known as bunions), and hammertoes with increased interdigital pressure, incurvated nail shape either from genetic or underlying bone developments (eg, subungual exostoses), and some medications (eg, epidermal growth factor receptor inhibitors and chemotherapy medications (gefitinib, cetuximab)).[4] Obesity can potentially exacerbate onychocryptosis by contributing to greater soft tissue mass throughout the body, particularly in the lower extremities. This can mimic periungual hypertrophy and exacerbate constriction from footwear. Similarly, diabetes, as well as thyroid, cardiac, and renal disorders, can increase lower extremity edema mimicking the effect of obesity on the nail unit.[5]

The possible involvement of intrinsic risk factors in the pathogenesis of ingrown toenails, eg, abnormal nail shape and anatomical abnormalities, has been widely debated. Some studies have found that pincer-nail deformity (see Image. Pincer Nails in a Female Patient), wide nail plates, congenital malalignment of the toenails, and thickening of the nail plate are possible risk factors for ingrown toenails.[3][6] Other literature suggests that bony abnormalities that increase internal pressure within the ankle, foot, or toe might contribute to the development of ingrown toenails.[1][7] However, more recent studies suggest no difference in the prevalence of anatomical abnormalities between patients with ingrown toenails and controls when proper footwear accommodation is implemented.[8]

Epidemiology

Few investigations of the epidemiology of ingrown toenails have been conducted. Previous studies have reported a prevalence of 2.5% to 5%.[7] The incidence and prevalence of ingrown toenails have increased in recent years, likely due to enhanced health literacy, and may also be related to lifestyle changes, eg, increased physical activity.

The incidence peaks in adolescence and early adulthood, with a clear male predominance, characterized by an approximate male-to-female ratio of 2:1. Ingrown toenails predominantly affect the hallux nail matrix and can involve 1 or more nail edges. Involvement of the lateral nail fold occurs approximately twice as frequently as the medial aspect, likely secondary to repetitive interdigital friction and compressive forces between adjacent toes.[7][9]

Pathophysiology

Many theories have been proposed to explain the onset of ingrown toenails. One assumption is that ingrown toenails are related to excess hypertrophic skin surrounding the nail. This is explained by wide lateral tissue tending to bulge around the nail, leading to pressure and necrosis (see Image. Ingrown Toenail, Necrosis).[10] However, the most widely accepted theory is that an ingrown toenail occurs when the nail plate edge grows into the overlapping lateral nail fold, with hyperkeratosis or hypertrophic changes in the skin, causing painful inflammation and the formation of hypergranulation tissue, often referred to as a pyogenic granuloma.[9][10] Reactive ground forces from athletic activity, obesity, warm and humid environments, and constricting footwear may increase the risk of ingrown nails.[2]

Histopathology

Histopathologic evaluation of ingrown toenails demonstrates epithelial disruption at the lateral nail fold with penetration of a nail spicule into the periungual soft tissue. This inciting mechanical insult results in an acute inflammatory infiltrate composed predominantly of neutrophils, often accompanied by edema and focal ulceration of the overlying epidermis. In chronicity, granulation tissue development is characterized by capillary proliferation, fibroblast activation, and a mixed inflammatory cell infiltrate. Long-standing lesions may additionally demonstrate epithelial hyperplasia and fibrosis of the surrounding nail fold.[11]

History and Physical

Patients with ingrown toenails most commonly present with localized pain along the lateral nail fold, exacerbated by shoe wear, ambulation, or direct pressure. The history frequently includes improper nail trimming, recent trauma, repetitive athletic activity, or the use of constrictive footwear. Patients may also report progressive swelling, erythema, drainage, or prior similar episodes. In advanced cases, symptoms of secondary infection, eg, purulent discharge or malodor, may be present.[9] 

Physical examination typically demonstrates tenderness to palpation along the affected nail border, with visible penetration of the nail plate into the periungual soft tissue. Early findings include mild erythema and edema of the lateral nail fold. As the condition progresses, granulation tissue, hypertrophy of the nail fold, and seropurulent drainage may be observed. Assessment should also evaluate for surrounding cellulitis, fluctuance suggestive of abscess, and risk factors, eg, diabetes or peripheral vascular disease.

Ingrown Toenail Staging

Clinical staging is most commonly performed using the following Heifetz classification system:

• Stage I: mild erythema, edema, and pain without purulence
• Stage II: increased inflammation with drainage and infection
• Stage III: chronic inflammation with granulation tissue formation and hypertrophy of the lateral nail fold [12][13]

The following additional classification system has been described by Kline et al:

• Stage 1: local irritation; no infection, pus, or granulation tissue
• Stage 2: infection without a history of onychocryptosis; pus and/or granulation tissue are present
• Stage 3: Infection with a history of more than one episode of onychocryptosis; pus and granulation tissue are present
• Stage 4: Infective onychocryptosis with partial onycholysis of a single nail border
• Stage 5: Infective onychocryptosis with partial onycholysis of both nail borders [14]

Evaluation

The diagnosis of an ingrown toenail is classically based on clinical features, but may require bacterial culture or standard radiographic evaluation if deeper infection of soft tissue or underlying bone is suspected. If physical examination reveals an abnormal nail shape consistent with subungual pathology, an x-ray examination may be used to rule out subungual or periungual exostosis. In rare cases, if the standard radiograph reveals bone pathology consistent with infection, an MRI may be ordered to rule out concomitant osteomyelitis. 

Treatment / Management

The natural history of untreated ingrown toenails is poorly supported by data, and no consensus on the best treatment technique exists.

General Conservative Measures

General measures for ingrown toenails include education on proper footwear and correct nail debridement: avoiding aggressive cutting of the lateral and distal margins of the nail plate (see Images. Schematic illustration of Taping, Ingrown Toenail, Packing, and Ingrown Toenail, Gutter Treatment). Simple nonsurgical palliative measures include correcting inappropriate footwear, managing hyperhidrosis and onychomycosis, soaking the affected toe, followed by applying a mid- to high-potency topical steroid, and placing wisps of cotton or dental floss under the ingrown lateral nail edge (see Images. Lateral Ingrown Toenail With Granulation, and Toenails, Onychogryphosis and Malalignment).[15] The application of topical steroids to hypertrophic granulation tissue may decrease inflammation.[10][16] Granulomatous tissue may also be treated with silver nitrate to reduce hypergranulation and excessive bleeding.

In cases of minor infection, including associated cellulitis or abscess formation, and in patients with high-risk comorbidities (eg, diabetes, immunosuppression), antibiotics (oral or topical) should be administered. Recent studies have concluded that polymicrobial infection/colonization is present in most ingrown nails in the fingers and toes. The most commonly cultured microorganisms were Enterococcus faecalis (14%), Staphylococcus aureus (12%), Candida albicans (9%), Enterobacter cloacae (8%), and Klebsiella pneumoniae (7%). Most cultured bacteria belonged to the Enterobacteriaceae family (36%), while other cultured bacteria included Staphylococci (26%), Enterococci (16%), Candida species (14%), and gram-negative non-fermenting bacilli (8%).[17] 

The color of the nail may assist in antibiotic treatment, with green often associated with Pseudomonas species. The most common antibiotics used to treat would include gram-positive coverage with some gram-negative coverage. A history of resistant bacterial infection may guide antibiotic coverage. Topical mupirocin or oral methicillin-resistant Staphylococcus aureus (MRSA) coverage would be indicated in these cases.

Patient history of diabetes, peripheral vascular disease, or autoimmune dysfunction should be taken into consideration. Use of topical or oral anti-inflammatories, a short course of oral non-steroidal anti-inflammatory drugs (NSAIDs), or steroids may help reduce the hyperinflammatory component of this condition, with or without surgical intervention. Pulsed dye laser (PDL) therapy at 595 nm, with vascular-targeting and anti-inflammatory effects, may serve as an effective adjunctive treatment.[18]

Surgical Techniques

Surgical procedures for ingrown toenails are performed under local anesthesia. Various techniques for local anesthesia exist, including digital block and metatarsal blocks. Local anesthetics (lidocaine and marcaine are most commonly used) in 0.25% to 2% concentrations can be used alone or in combination. Indications for local anesthesia depend mainly on the type of procedure and the clinician's preference. Epinephrine may be added to the local anesthetic solution to minimize bleeding; commonly used concentrations include 1:200,000 or 1:400,000, prepared by combining a plain anesthetic agent with a formulation containing premixed epinephrine.

Surgical options for ingrown toenails include: 

• Spicule excision and partial surgical matricectomy: This consists of excising the affected nail portion with a partial mechanical matricectomy.[19]
(B2)

• Chemical partial matricectomy: Chemical matricectomy is commonly performed using 89% phenol (care must be taken, as this agent is highly flammable and will affect any skin surface). This procedure demonstrates a higher success rate and is less painful than mechanical/surgical matricectomy, and its success depends on good hemostasis. Other chemical agents, eg, sodium hydroxide and trichloroacetic acid, can be employed.[20]
(A1)

• Wedge resection of the toenail and nail fold: This approach consists of the excision of the affected portion of the nail plate, partial matrixectomy, and wedge dissection of the nail bed and the hypertrophic nail fold. Clinicians should generally avoid this technique unless other methods have failed (see Image. Wedge Excisions).

• Excision of the affected nail and total matricectomy: This is a more invasive treatment for ingrown toenails and includes excision of the affected nail and nail bed, with a total matricectomy (chemical or mechanical/surgical). This procedure is indicated for stage IV ingrown toenails, onychogryphosis, onychodystrophy, and recurrence.

• Soft-tissue nail fold excision technique: This procedure does not touch the nail; the nail is theorized not to be the causative factor in developing ingrown toenails. This procedure consists of a wide excision of the soft tissue on the medial and/or lateral nail folds.[21][22]
(B2)

• Other techniques: Newer techniques, including electrocautery, radiofrequency ablation, and carbon dioxide laser ablation, have become the newest form of ingrown toenail management.[3][10][23]

Surgical treatment options for ingrown toenails are numerous, and little consensus exists on the technique of choice, except that removal of enough nail and tissue to ensure a low rate of recurrence is preferred. The ideal procedure should lead to the best functional and aesthetic outcome (see Images. Fusiform Excision, Matrix Horn Resection, Lateral Matrix Horns, Lateral Matrix Horn Phenolization, and Phenolization, Lateral Matrix Horn).

Prior studies have concluded that antibiotic treatment and simple nail avulsions, partial or complete without matrixectomy, lead to high recurrence rates, while phenol or surgical matrixectomy has shown greater success. Ultimately, the patient and treating clinician must weigh the benefits of any treatment plan together. Consideration of microscopic biopsy analysis is advisable in any recurrent or nonhealing case.

Differential Diagnosis

Differential diagnosis includes hallux extensus (ski jump hallux at the interphalangeal joint), subungual exostosis, osteochondroma, and tumors of the nail bed or nail folds (benign and malignant). If suspected, an x-ray examination that reveals the subungual bony proliferation can confirm the diagnosis of subungual bone tumor or distant trauma with hypertrophic remodeling. Malignant tumors to consider are subungual melanoma, including amelanotic melanoma and subungual squamous cell carcinoma, which can be locally aggressive.[2][10][24][25][26][27][28][29][30]

Prognosis

Recurrences can occur following all the abovementioned procedures; they result from incomplete matricectomy and regrowth of a spicule from the lateral horn. Simple nail avulsion has the highest recurrence rate (70%). Chemical matricectomy and laser matricectomy showed lower recurrence rates than mechanical matricectomy.[13]

Complications

Secondary infection of the nail fold, paronychia, and scarring of the nail fold are essential to consider and treat.