Corns, Calluses and Intractable Plantar Keratosis
- Plantar keratoses are HYPERKERATOSES - localised thickening of the stratum corneum - produced by repetitive PRESSURE and SHEAR on the skin; the body lays down keratin to protect a focal high-load area, but the thickened skin then itself becomes a painful prominence.
- Distinguish: a CALLUS (tyloma) is a DIFFUSE plaque over a broad weight-bearing area; a CORN (heloma) is FOCAL with a central keratin CORE - 'durum' (hard) over a bony prominence, 'molle' (soft, macerated) in a web space (classically the 4th); an INTRACTABLE PLANTAR KERATOSIS (IPK) is a discrete deep plug directly UNDER A METATARSAL HEAD.
- The cause is almost always ABNORMAL/FOCAL LOAD: a prominent or plantarflexed metatarsal head (or a prominent fibular condyle of the metatarsal head), equinus/tight gastrocnemius, claw or hammer toes, hallux valgus, pes cavus, prior surgery, or ill-fitting footwear - so treatment must address the underlying mechanics, not just the skin.
- A key exam point is differentiating an IPK from a PLANTAR WART (verruca): an IPK lies over a weight-bearing BONY point, the normal SKIN LINES (dermatoglyphics) run THROUGH it, it is tender to DIRECT pressure, and paring reveals only keratin; a VERRUCA can be anywhere, INTERRUPTS the skin lines, is tender to LATERAL pinch/squeeze, and paring reveals PINPOINT BLEEDING from thrombosed capillaries (black dots).
- In the patient with DIABETES (or neuropathy), a plantar callus is a PRE-ULCERATIVE sign - the high pressure under the callus causes underlying tissue breakdown and ulceration - so calluses must be regularly DEBRIDED and the area OFFLOADED; patients themselves often fail to notice these lesions.
- Management is CONSERVATIVE first: regular paring/debridement, padding and OFFLOADING (metatarsal dome/bar, accommodative orthoses), well-fitting/wide footwear, emollients (urea/salicylic-acid keratolytics), and correcting the cause; SURGERY is reserved for refractory IPK and aims to relieve the pressure - condylectomy (DuVries) of a prominent fibular condyle or a metatarsal OSTEOTOMY to elevate/shorten a plantarflexed metatarsal, and correction of associated toe/forefoot deformity - but carries a real risk of TRANSFER LESIONS under adjacent metatarsals.
- “Callus = diffuse (no core); corn = focal with a core (durum over bone, molle in the web); IPK = discrete plug under a met head.
- “IPK vs verruca: IPK keeps skin lines + tender to DIRECT pressure + no bleeding on paring; verruca interrupts skin lines + tender to PINCH + pinpoint bleeding.
- “Diabetic callus = pre-ulcer sign (debride + offload). Surgery for IPK relieves pressure but can cause TRANSFER lesions.
Over a weight-bearing bony point (met head). Skin lines run through it. Tender to direct pressure. Paring = keratin only, no bleeding.
Anywhere on the sole. Interrupts skin lines. Tender to lateral pinch/squeeze. Paring = pinpoint bleeding (thrombosed capillaries / black dots).
Types & Pathogenesis
Repetitive pressure and shear drive the epidermis to thicken its stratum corneum. A callus (tyloma) is the diffuse form over a broad load area; a corn (heloma) is the focal form with a central keratin core that presses inward like a nail and causes sharp pain - hard (durum) over a bony prominence (the dorsum or tip of a clawed/hammered toe, or a metatarsal head) and soft (molle), white and macerated, in a moist web space (classically the 4th) where adjacent phalangeal condyles rub. An intractable plantar keratosis (IPK) is a discrete deep plug directly under a metatarsal head, usually because that metatarsal is prominent or plantarflexed or has a prominent fibular condyle. The common thread is abnormal mechanics, so durable treatment means correcting the load.
Assessment
Examine the lesion's site and its relation to a bony prominence, the foot's deformities (claw/ hammer toes, hallux valgus, cavus, prominent/plantarflexed metatarsal, equinus), and the footwear. Pare the lesion to differentiate an IPK/callus (keratin only, preserved skin lines, tender to direct pressure) from a verruca (pinpoint bleeding, interrupted skin lines, tender to lateral pinch). Assess sensation and vascular status - critical in diabetics, where a callus is a pre-ulcer marker. Weight-bearing radiographs help identify a prominent or plantarflexed metatarsal, a long metatarsal, or a prominent fibular condyle when planning surgery.
Management
- Conservative (first line): regular paring/debridement; padding and offloading with a metatarsal dome/bar, accommodative orthoses and cushioned, wide, low-heeled footwear; emollients/keratolytics (urea, salicylic acid); and treating the underlying deformity non-operatively. For a soft corn, keep the web dry and separate the toes.
- Diabetic/neuropathic foot: regular professional debridement + offloading to prevent the callus progressing to ulceration; multidisciplinary diabetic-foot care.
- Surgery (refractory IPK / corns): aim to relieve the focal pressure -
- DuVries condylectomy: excise the prominent fibular (plantar) condyle of the metatarsal head under a discrete IPK.
- Metatarsal osteotomy (e.g. distal/BRT/Weil-type) to elevate or shorten a plantarflexed/long metatarsal.
- Correct the deformity driving a corn: hammer/claw toe correction, condylectomy of a phalangeal condyle for a soft corn, hallux valgus correction.
- Simply excising the skin lesion alone does NOT work - it recurs unless the bony cause is addressed.
Metatarsal surgery for an IPK relieves the treated ray but commonly creates a TRANSFER LESION - a new plantar keratosis (transfer metatarsalgia) under an adjacent metatarsal head whose relative load has increased - and may precipitate a hammer-toe of the operated ray. In one long-term series of distal metatarsal osteotomies for intractable plantar callosity, although most callosities healed, new transfer callosities and hammer-toe deformities developed over time. Counsel patients accordingly, balance the rays carefully, and exhaust conservative care first - especially in low-demand or vasculopathic/diabetic patients.
Evidence & Key Studies
Straight (transverse distal) metatarsal osteotomy for the treatment of plantar callosities
- In 25 intractable plantar callosities treated by transverse distal metatarsal osteotomy, 23 had healed at 7-year follow-up (two after re-osteotomy).
- However, eight hammer-toe deformities developed in operated rays and eight new plantar callosities developed under adjacent (non-operated) rays - i.e. transfer lesions.
- Metatarsal osteotomy is effective for intractable plantar callosity but transfer lesions and hammer toes tend to develop over time - a key counselling point.
Differences between patient-reported and clinician-observed nonulcerative foot signs in diabetes
- Calluses and corns are recognised non-ulcerative (pre-ulcerative) foot signs in patients with diabetes at risk of foot ulceration.
- Patients poorly self-identified these lesions (sensitivity ~51% for calluses and ~44% for corns), so many high-pressure lesions go unnoticed by the patient.
- Supports professional surveillance, debridement and patient education/offloading to reduce diabetic foot ulcer risk.
According to PubMed, the efficacy of metatarsal osteotomy for IPK and the development of transfer lesions/ hammer toes come from the cited Kiviniemi series, and the pre-ulcerative significance of calluses/corns in diabetes (and patients' poor self-recognition) from the cited Takehara study. The corn/callus/IPK definitions and the IPK-versus-verruca differentiation are standard clinical teaching. (See also our Metatarsalgia, Lesser Toe Deformities and Diabetic Foot topics.)
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A patient has a painful discrete callus under the second metatarsal head. How do you confirm it is not a wart, and how would you manage it?”
“Why does a plantar callus matter more in a patient with diabetes, and how does that change your management?”
Mnemonics & Memory Aids
LINES
Hook:Skin LINES through it + direct-pressure pain + no bleeding = IPK, not a verruca.
PADS
Hook:Treat with PADS - offload first, surgery (with transfer-lesion caution) last.
Definitions
- Callus (tyloma): diffuse, no core
- Corn (heloma): focal + central core - durum (over bone), molle (web space, macerated)
- IPK: discrete deep plug under a metatarsal head
IPK vs verruca
- IPK: over bony point, skin lines THROUGH it, tender to DIRECT pressure, keratin only
- Verruca: anywhere, INTERRUPTS skin lines, tender to PINCH, pinpoint bleeding on paring
- Pare the lesion to differentiate
Cause & diabetic significance
- Abnormal load: prominent/plantarflexed metatarsal, fibular condyle, claw/hammer toes, cavus, equinus, footwear
- Diabetic callus = PRE-ULCER sign (debride + offload)
- Patients under-recognise their own calluses
Management
- Conservative: pare/debride, offload (met dome/orthoses), footwear, keratolytics, treat deformity
- Soft corn: keep web dry + separate toes
- Surgery (refractory): DuVries condylectomy / metatarsal osteotomy -> beware transfer lesions