Knuckle Pads (Heloderma, Athlete's Nodules, Surfer's Nodules, Running/Nike Nodules, Subcutaneous Fibroma, Keratosis Supracapitularis, Discrete Keratoderma, Tylositas Articuli)

Are You Confident of the Diagnosis?

What you should be alert for in the history

Knuckle pads (KPs) are benign, usually asymptomatic growths on the extensor surfaces of the hands, mostly located over the proximal interphalangeal (PIP) joints, and to a lesser degree the metacarpophalangeal (MCP) and distal interphalangeal (DIP) joints.

Upon taking the patient’s history, one should ask about repetitive trauma as a clue to the diagnosis, as this is thought to be the primary cause.

Characteristic findings on physical examination

Physical exam reveals 0.5-4cm flesh-colored hyper- or hypopigmented papules, nodules, or plaques with variable keratinization which are well defined, freely moveable, and firm (Figure 1, Figure 2). They may be single or multiple in number.

Figure 1.

Knuckle pads in a patient that works as a hardwood floor installer.

Figure 2.

Surfer nodule.

Expected results of diagnostic studies

Although the diagnosis is mostly clinical, histopathological examination reveals two patterns. The first is an epidermal pattern with hyperkeratosis, acanthosis, and discrete fibroblast proliferation. The second is a dermal pattern with marked fibroblast proliferation, thickened collagen fibers, and occasionally, hyperkeratosis. Dilated capillaries in the papillary dermis and little to no inflammation is seen in both patterns. There is no “owl eye halo” remniscent of warts.

Diagnosis confirmation

Differential diagnosis includes:

– granuloma annulare (annular brown-red dermal plaques with minimal to no surface change, typically starts as a papule)

– erythema elevatum diutinum (papules and nodules of the extensor surfaces, slightly tender)

– foreign body reaction (solitary inflammed tender papule/nodule)

– xanthomas (yellowish orange papules, plaques, not in an annular configuration)

– gouty tophi (dermal nodules)

– scars/keloids (thick firm dermal plaques and nodules in an area of trauma)

– verrucae (papules and plaques with a rough verrucal surface, and punctate black dots representing thrombosed vessels)

– rheumatoid nodules (dermal nodules overlying extensor joints in patients with rheumatoid arthritis [RA])

– Heberden’s nodes (bony nodules at the PIP joint seen in osteoarthritis)

– callouses (thickening of the skin from chronic friction/mechanical trauma, most often localized to palmar surface of hands)

– fibromas (dermal papules and nodules)

– pachydermodactyly

Pachydermodactyly is an acquired form of digital fibromatosis with diffuse enlargement of the phalanges that occurs in young males. KPs, in contrast, can affect males or females and usually do not affect the lateral aspects of the fingers.

Any area subjected to repeated trauma can give rise to lesions similar to KPs, and these lesions have been referred to as helodermas, tylositas articuli, discrete keratodermas, and subcutaneous fibromas.

The term athlete’s nodules has been attributed to a group of benign acquired collagenous growths that include KPs (dorsal fingers), surfer’s nodules (dorsal feet), and running shoe or Nike nodules (dorsal toes at sites of increased pressure from shoes).

Who is at Risk for Developing this Disease?

KPs were first described by Garrod in 1893, and also have been depicted in various works by Michaelangelo, including David (on the statue’s right thumb).

Patients at risk for KPs are usually those who participate in activities involving repetitive trauma to the dorsal hands.

KPs are divided into primary and secondary (acquired) subtypes. Primary KPs can be idiopathic, sporadic (usually in children or young adults), or inherited in an autosomal dominant pattern.

KPs have been associated with autosomal dominant palmoplantar keratoderma (with or without ichthyosis vulgaris), acrokeratoelastosis of Costa, keratoderma hereditaria mutilans, pseudoxanthoma elasticum, Bart Pumphrey Syndrome (leukonychia, mixed sensorineural deafness, and KPs), and fibromatoses such as Dupuytren (palmar fibromatosis), Ledderhose (plantar fibromatosis), and Peyronie (penile fibromatosis) diseases.

Secondary (acquired) KPs are also known as pseudo-KPs or false-KPs. These are caused by repetitive external trauma, and are either occupational (mechanics, live chicken hangers, carpet layers, plumbers, tailors, textile workers), sports/activity related (boxers, surfers, football players, video game enthusiasts, marble players), or are associated with psychiatric disturbances giving rise to repetitive compulsive behavior (biting/chewing, bulimia).

What is the Cause of the Disease?

KPs are a process involving localized superficial fibromatosis. There is a proliferative phase, followed by a fibrotic stage, and the nodule grows by expansion towards the epidermis and surface of the skin. The etiology of KPs may be idiopathic or genetic, but KPs are usually acquired in response to repetitive frictional pressure and trauma.


KPs grow over a period of months to years, and usually do not all appear at once, but rather appear sequentially. Of interest, they also occur frequently in large apes that have a tendency to walk on their knuckles. They may be observed in adults or children. Development in children is usually associated with the patient biting, sucking, or pulling on their fingers. The prevalence of this condition is unclear, as in many cases patients do not seek a diagnosis or treatment, or consult a dermatologist .

Systemic Implications and Complications

KPs can be associated with other disorders such as palmoplantar keratoderma (with or without ichthyosis vulgaris), acrokeratoelastosis of Costa, keratoderma hereditaria mutilans, pseudoxanthoma elasticum, Bart Pumphrey Syndrome (leukonychia, mixed sensorineural deafness and KPs), and fibromatoses such as Dupuytren, Ledderhose, and Peyronie diseases. Patients with Dupuytren contractures are four times more likely to develop KPs.

Complications of KPs can involve limited mobility of the fingers and difficulty with hand and finger dexterity. Patients may have difficulty wearing rings, and may occasionally experience mild tenderness. Additionally, many patients develop cosmetic concerns as a result of KPs.

Treatment Options



-Keratolytics (urea 10 -20% cream once to twice daily, salycilic acid 6% gel once daily, lactic acid 5% or 12% lotion twice daily)

-Intralesional (corticosteroids, 5-fluorouracil)


Excision with a 1-2mm margin (only practical for small symptomatic lesions that fail topical therapy, as recurrence rates are high if the inciting events are not removed).


-Eliminate the source of repetitive trauma (may involve psychotherapy/behavioral modification)

-Protective gloves, casts, or splints

-Silicone gel sheeting


-Radiation: local (reported, but not recommended)

-Solid carbon dioxide laser

Optimal Therapeutic Approach for this Disease

Eliminating the source of repetitive trauma is the most important and effective method of treatment and prevention of KPs. Some cases may require behavioral or psychological intervention. Modification of occupational or recreational activities should be sought if these are the source of the repetitive trauma. As some KPs resolve spontaneously, removal of the stimulus may be all the treatment that is needed.

Addition of protective barriers such as gloves, casts, or splints may be necessary. Silicone sheets have been shown to decrease the size of KPs and also may act as a protective barrier against external trauma.

Keratolytics such as urea have been shown to decrease the size of lesions. Salicylic acid preparations have not been proven as effective as urea, but a trial may be warranted due to their low side effect profile.

Intralesional corticosteroids have been shown to decrease lesion size, presumably secondary to dermal atrophy and inhibition of collagen synthesis. Intralesional 5-fluorouracil is also effective in decreasing lesion size by inhibiting fibroblast proliferation. These treatments may not be as appropriate in children, as they are painful. Corticosteroids also carry with them the risk of epidermal atrophy and telangiectasia formation.

Potent topical steroids may be tried because of their low side effect profile, though KPs have shown little response to this modality.

Surgery may be indicated, especially if there is functional impairment caused by KPs, although there is risk of hypertrophic scarring or keloid formation, resulting in cosmetic issues or decreased range of motion after surgery due to scarring.

Solid carbon dioxide treatment has also been shown to decrease lesion size, but this treatment also can be quite painful.

Patient Management

Close clinical followup is imperative, as KPs are prone to recurrence after treatment, and patients may need additional assistance in eliminating the source of repetitive trauma. Additionally, corticosteroid or 5-fluorouracil injections may be needed to treat developing keloids or hypertrophic scars following surgery.

Combination therapy with less invasive measures such as behavioral modification, topical urea preparations, and intralesional corticosteroids or 5-fluorouracil may be required, with or without surgery, for more refractory lesions or to address greater functional impairment caused by KPs.

Surgery may also be complicated by scar formation involving other functional structures of the hands such as tendons or fascia, and therefore the patient may benefit from skilled excision of the lesions by a hand surgeon, and may need physical therapy following surgery. Prophylactic dermatofasciectomy has also been advocated by some to prevent recurrence following surgical removal of KPs.

The patient’s expectations must be made clear before initiating treatment, as KPs can be quite refractory to treatment and are prone to recurrence.

Unusual Clinical Scenarios to Consider in Patient Management

Patients may benefit from family involvement or referral to psychiatry if a psychiatric disturbance or compulsion is suspected.

Patients may not have the option to alter their occupation, making elimination of the repetitive trauma difficult.

KPs can be associated with other disorders such as palmoplantar keratoderma (with or without ichthyosis vulgaris), acrokeratoelastosis of Costa, keratoderma hereditaria mutilans, pseudoxanthoma elasticum, Bart Pumphrey Syndrome (leukonychia, mixed sensorineural deafness and KPs), and fibromatoses such as Dupuytren, Ledderhose, and Peyronie diseases. Patients with Dupuytren contractures are four times more likely to develop KPs.

Pachydermodactyly is an acquired form of digital fibromatosis that occurs in young males and causes diffuse enlargement of the phalanges.

What is the Evidence?

Weiss, E, Amini, S. “A novel treatment for knuckle pads with intralesional fluorouracil”. Arch Dermatol. vol. 143. 2007. pp. 1458-60. (Case report of using 5-fluorouracil intralesionally for the treatment of KPs . Discusses response and side effects. This was the first published report utilizing intralesional fluorouracil in the treatment of KPs . The patient had near complete remission at 9 months after just one treatment for her KPs.)

Yebenes, M, Garcia, X, Gilaberte, M. “Acquired fusiform swelling of the fingers”. Arch Dermatol. vol. 141. 2005. pp. 1035-6, 1038-9. (Case report of pachydermodactyly. Describes the distinction of pachydermodactyly from KPs.)

Kodama, BF, Gentry, RH, Fitzpatrick, JE. “Papules and plaques over the joint spaces. Knuckle pads (heloderma)”. Arch Dermatol. vol. 129. 1993. pp. 1044-5, 1047. (Short paper reviewing etiology of KPs, differential diagnosis, and other fibrosing disorders.)

Koba, S, Misago, N, Narisawa, Y. “Knuckle pads associated with clubbed fingers”. J Dermatol. vol. 34. 2007. pp. 838-40. (Highlights a case of knuckle pads in association with clubbed fingers, a previously unpublished association.)

Rushing, ME, Sheehan, DJ, Davis, LS. “Video game induced knuckle pad”. Pediatr Dermatol. vol. 23. 2006. pp. 455-7. (Case report of a novel way of developing KPs.)

Allison, JR, Allison, JR. “Knuckle pads”. Arch Dermatol. vol. 93. 1966. pp. 311-6. (Likely one of the first descriptions of the condition. Well written and informative.)

Tompkins, SD, McNutt, NS, Shea, CR. “Distal pachydermodactyly”. J Am Acad Dermatol. vol. 38. 1998. pp. 359-62. (A similar condition to KPs . Paper is a short review of the condition.)

Barnes, CJ, Davis, L. “Knuckle pads”. Emedicine. (Comprehensive, well written, and current.)

Codispoti, A, Colombo, E, Zocchi, L, Serra, V, Pertusi, G, Leigheb, G. “Knuckle pads, in an epidermal palmoplantar keratoderma patient with Keratin 9 R163W transgrediens expression”. Eur J Dermatol. vol. 19. 2009. pp. 114-8. (Case report of a patient with KPs, PPK ,and a Keratin 9 mutation.)