Background
An ingrown nail (onychocryptosis) is a fairly frequent problem resulting either from growth of the nailfold inward into the nailbed or from abnormal embedding of the nail plate into the nail groove, causing significant discomfort. Although the terms ingrown nail (see the first image below) and paronychia (see the second image below) are often thought to be synonymous, they refer to different conditions, both of which can cause significant discomfort. Ingrown toenails may cause pain with ambulation.
Mild cases can generally be treated by means of conservative nonsurgical methods. [1] (See Treatment.) General use of oral antibiotics is not supported. Surgery may be considered for cases that are more severe or are refractory to conservative treatments. [2]
Pathophysiology
Ingrown nails result from an alteration in the proper fit of the nail plate in the usual nail groove. Sharp spicules of the lateral nail margin develop and are gradually driven into the dermis of the nail groove. The nail thus acts as a foreign body. An inflammatory response occurs in the area of penetration, leading to erythema, edema, purulence, and development of granulation tissue.
The normal distance between the nail groove and the border of the nail is 1 mm. A thin epithelial layer covers the nail groove and protects it from irritation. With increased pressure on the nailbed and nail groove, an epidermal breakage occurs, with subsequent inflammation, pain, and infection. [3]
Ingrown nails generally occur as the result of poorly fitted footgear. However, they may also be caused by prior trauma to or abnormal shape of the nail margin. [4]
Types of ingrown nail include the following [5] :
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Neonatal - This type occurs as a result of delayed overgrowth of the free nail margin on the tip of the toe (see the first image below); it can be managed conservatively
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Infantile - This congenital form results from malalignment of the great toenail or from hypertrophy of the lateral nailfold
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Adolescent - The most common cause is a narrow nailbed, resulting in ingrowth of the distal lateral nail
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Adult - The most common cause is pressure that causes a sharply bent lateral margin of the nail plate
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Distal embedding from a great toenail that is too short
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Retronychia - This is a rare variant of ingrown nail in which the nail plate is embedded into the proximal nail fold with subsequent inflammation of the proximal nailfold [6]
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Pincer nail (see the second image below)
Neonatal ingrown nail. Image from Haneke E. Controversies in the treatment of ingrown nails. Dermatology Research and Practice. 2012; 2012:783924.
Pincer nail. Image from Haneke E. Controversies in the treatment of ingrown nails. Dermatology Research and Practice. 2012; 2012:783924.
Etiology
The following factors have been implicated in the development of ingrown nails:
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Improper trimming of toenails - Cutting the toenail so that it is rounded, V-shaped, or too short will cause bulging of the soft tissue and the possibility of leaving a nail spur that is difficult to remove, resulting in an inflammatory reaction with pressure necrosis; the proper way to trim the toenail is to cut it straight across beyond the nail bed [7]
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Poorly fitting shoes - The nail plate can be forced out of the nail groove by footwear that has a toe box that is too small for the forefoot; the constant pressure on the nailbed and nail groove results in breakage that starts an inflammatory process and eventually results in an ingrown nail
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Nail plate abnormality - Increased curvature of the nail plate, as in pincer nail, may develop into an ingrown nail [7] ; deformities that result from prior trauma or underlying bone pathology may predispose to ingrown nails
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Excessive sweating - Ingrown nails are known to be common among teenagers and soldiers, in whom excessive sweating is present, which results in softening of the nailfold; with the participation in sports, nail spicules may develop that can easily pierce the adjacent softened nail fold
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Obesity - This can cause deepening of the nail groove
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Generalized joint hypermobility - Joint hypermobility from changes in foot biomechanics and gait increases medial midfoot pressure and loading during walking; because the first metatarsophalangeal (MTP) joint bears the most pressure, an ingrown toenail may develop in the big toe [12]
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Onychomycosis - This infection may result in brittle nails, which may form nail spicules and pierce the adjacent nailfold
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Heredity - Some people are genetically predisposed to inwardly curved nails, with distortion of one or both nail margins
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Pathologic hallux interphalangeal angle (≥14.5) - This abnormality has been correlated with the development of an ingrown hallux nail and may act as a predisposing factor [13]
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Paronychia with sporangium formation - This has been reported to cause an ingrown nail [14]
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Hematopoietic stem cell transplantation - Children who undergo this procedure have a higher incidence of ingrown nails and have been found to have the aggressive forms, with more than 50% having nail edge and bilateral great-toe involvement and 37.5% experiencing recurrence [15]
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Harder nails - Young male runners with a hard nail consistency have been found to have a higher incidence of ingrown nails [16]
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Diabetes - The prevalence of ingrown nails has been found to be higher in diabetic patients, suggesting a role for diabetic vasculopathy in the development and evolution of ingrown nails [17]
Epidemiology
United States and international statistics
In the United States, onychocryptosis is the most common of all nail problems. Toenails are affected much more commonly than fingernails. The lateral margins of the great toe are most frequently affected.
In the United Kingdom, approximately 10,000 cases have been reported annually. In a Korean epidemiologic study, the 10-year overall incidence was found to be 307.5 cases per 100,000 persons, with an upward trend. [18]
Age-, sex-, and race-related demographics
Ingrown nails may be observed in people of all ages but are most common in the second decade of life. They become much more common as children begin bearing weight on their feet and wearing shoes, though congenital onychocryptosis has been described, [19, 20] as have cases in infants. [21]
The reported male-to-female ratio is 3:1. In reported cases of retronychia, a female predominance has been noted. [6] A 2018 epidemiologic study revealed increased incidence and a higher prevalence in females. [18]
No racial predilection has been identified.
Prognosis
The prognosis is excellent. Complete healing is expected. Mortality generally is not associated with ingrown nails, and morbidity is chiefly the result of infection of the tissues. If treatment is neglected, abscess formation (paronychia) may occur, and infection may spread and lead to osteomyelitis, systemic infection, sepsis, or amputation.
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Right great-toe paronychia in 3-year-old child. Image from Ann G Egland, MD.
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Preparing for digital block before surgical treatment of paronychia of right great toe. Universal precautions should always be observed. Image from Ann G Egland, MD.
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Neonatal ingrown nail. Image from Haneke E. Controversies in the treatment of ingrown nails. Dermatology Research and Practice. 2012; 2012:783924.
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Pincer nail. Image from Haneke E. Controversies in the treatment of ingrown nails. Dermatology Research and Practice. 2012; 2012:783924.
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Stage 3 ingrown nail. Image from Wikimedia Commons.
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Schematic view for cotton wick insertion. Image from Haneke E. Controversies in the treatment of ingrown nails. Dermatology Research and Practice. 2012; 2012:783924.
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Schematic view illustrating taping of nail. Image from Haneke E. Controversies in the treatment of ingrown nails. Dermatology Research and Practice. 2012; 2012:783924.
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Schematic view illustrating gutter technique. Image from Haneke E. Controversies in the treatment of ingrown nails. Dermatology Research and Practice. 2012; 2012:783924.
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Hypertrophy of lateral nailfold that partially covers nail. Image from Haneke E. Controversies in the treatment of ingrown nails. Dermatology Research and Practice. 2012; 2012:783924.
