High-yield overview

Corns, Calluses and Intractable Plantar Keratosis

PressureHyperkeratosis from focal load

IPKDiscrete keratosis under a met head

vs VerrucaSkin lines preserved; no pinpoint bleeding

DiabeticCallus = pre-ulcer sign (offload!)

The plantar keratoses

Callus (tyloma)

PatternDIFFUSE thickening of the stratum corneum over a broad weight-bearing area (e.g. ball of the foot, heel) - no central core.

Treatment

Hard corn (heloma durum)

PatternFOCAL keratosis with a central conical KERATIN CORE, typically over a bony prominence (dorsum/tip of a lesser toe or under a metatarsal head).

Treatment

Soft corn (heloma molle)

PatternMacerated white corn in a WEB SPACE (classically the 4th interdigital space) from opposing condyles + moisture.

Treatment

Intractable plantar keratosis (IPK)

PatternA DISCRETE, deep, painful keratotic plug directly under a METATARSAL HEAD (often a prominent fibular condyle or a plantarflexed metatarsal) - the 'intractable' forefoot callus.

Treatment

Critical Must-Knows

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.

Clinical Pearls

“
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.

Types & Pathogenesis

Keratin as a response to load. Repetitive pressure and shear drive the epidermis to thicken its stratum corneum. The keratin is laid down to protect a focal high-load area, but the thickened skin then becomes a painful prominence in its own right.

The four lesions. A callus is the diffuse form and a corn the focal one. The corn has a central keratin core that presses inward like a nail and causes sharp pain.

Callus (tyloma). Diffuse thickening over a broad weight-bearing area, such as the ball of the foot or the heel, with no central core.
Hard corn (heloma durum). Over a bony prominence: the dorsum or tip of a clawed or hammered toe, or a metatarsal head.
Soft corn (heloma molle). White and macerated, in a moist web space (classically the 4th) where the condyles of adjacent phalanges rub.
Intractable plantar keratosis (IPK). A discrete, deep, painful 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 load. The cause is almost always abnormal or focal load: a prominent or plantarflexed metatarsal head or a prominent fibular condyle, equinus or a tight gastrocnemius, claw or hammer toes, hallux valgus, pes cavus, prior surgery, or ill-fitting footwear. Durable treatment therefore means correcting the mechanics, not just the skin.

Clinical photograph of both soles: a discrete yellow keratosis beneath the forefoot of one and broader callosity over the ball of the foot and great toe of the other — Plantar hyperkeratoses on both soles: a discrete yellow keratosis beneath one forefoot, and broader callosity over the ball of the foot and great toe of the other. Both sit on high-pressure contact areas; in a neuropathic or diabetic foot either pattern is a pre-ulcer warning.Credit: Jmarchn, Wikimedia Commons — CC BY-SA 3.0

The Metatarsal Parabola: Why One Ray Overloads (and Transfer Lesions)

The normal cascade. Normal forefoot load is a harmonious cascade in which the metatarsal heads share weight in a smooth parabola. The second metatarsal is usually the longest, the others are progressively shorter from the second to the fifth, and the first ray, with its sesamoids, carries its share.

Why one ray overloads. A metatarsal that is relatively long or plantarflexed, or that carries a prominent plantar (fibular) condyle, bears excess focal pressure, and an IPK forms under it. An insufficient or hypermobile first ray, as in hallux valgus or after a failed bunion operation, shifts load laterally to the second and third heads. Equinus raises pressure across the whole forefoot.

Why the lesion moves. Osteotomy aims to restore the parabola by shortening or elevating the offending metatarsal. Over-correcting or unbalancing the cascade shifts the relative load to an adjacent head and produces a new IPK, the transfer lesion, which is why the rays must be balanced. General forefoot overload is covered in Metatarsalgia.

Discrete vs Diffuse IPK (and the Porokeratosis Mimic)

The two IPK patterns change the operation, and one look-alike is not an IPK at all.

Discrete IPK. A single, well-defined plug under one metatarsal head, classically over a prominent plantar (fibular) condyle. The focal prominence is removed by DuVries condylectomy or a focal elevating osteotomy.

Diffuse IPK. A broader keratosis under several metatarsal heads, often the central ones, reflecting a global forefoot overload: a long or plantarflexed metatarsal cascade, equinus or a tight gastrocnemius, pes cavus, or first-ray insufficiency. Treatment addresses the global cause, for example a gastrocnemius recession for equinus, rebalancing the cascade or correcting the cavus, rather than a single condylectomy.

The look-alike: porokeratosis plantaris discreta. A deep, sharply demarcated, very tender keratotic plug arising from a sweat (eccrine) duct. It is not over a bony prominence and is pressure-independent, so although it mimics an IPK it will not respond to a metatarsal osteotomy. Recognising it avoids a futile operation; the lesion itself is excised or treated.

Assessment

Find the bony cause. Examine the lesion's site and its relation to a bony prominence, then the foot's deformities (claw or hammer toes, hallux valgus, cavus, a prominent or plantarflexed metatarsal, equinus) and the footwear.

Clinical plantar view showing a focal keratosis directly beneath the tibial sesamoid — A focal keratosis (arrowhead) lies directly beneath the tibial sesamoid. Map the skin lesion to the overloaded bony structure: treating the keratin alone cannot remove the pressure source.Credit: Nakajima K et al. (PMC12608295) — CC BY 4.0

Pare it: IPK or verruca? This is the classic question. Paring and examining the lesion separates an IPK or callus from a plantar wart.

Site

IPK or callus: Over a weight-bearing bony point (metatarsal head)
Verruca (plantar wart): Anywhere on the sole

Skin lines (dermatoglyphics)

IPK or callus: Run through the lesion
Verruca (plantar wart): Interrupted

Tenderness

IPK or callus: To direct pressure
Verruca (plantar wart): To lateral pinch or squeeze

On paring

IPK or callus: Keratin only, no bleeding
Verruca (plantar wart): Pinpoint bleeding from thrombosed capillaries (black dots)

	IPK or callus	Verruca (plantar wart)
Site	Over a weight-bearing bony point (metatarsal head)	Anywhere on the sole
Skin lines (dermatoglyphics)	Run through the lesion	Interrupted
Tenderness	To direct pressure	To lateral pinch or squeeze
On paring	Keratin only, no bleeding	Pinpoint bleeding from thrombosed capillaries (black dots)

Close-up photograph of a plantar wart showing interrupted skin lines around a yellowish keratotic lesion with visible pinpoint dark dots from thrombosed capillaries — A plantar wart: the skin (dermatoglyphic) lines are interrupted as they reach the lesion, and small dark pinpoint dots, thrombosed capillaries, sit within its yellowish keratotic surface.Credit: Harrygouvas, Wikimedia Commons — CC BY-SA 3.0

Dermoscopy of a pared plantar wart showing frogspawn-like white halos and central capillary dots — Dermoscopy of a pared plantar wart: a frogspawn pattern of white halos around red-black capillary dots. A pared IPK yields only translucent keratin.Credit: Bristow I et al. (PMC9779159) — CC BY 4.0

Sensation and circulation. Assess sensation and vascular status. This is critical in the patient with diabetes, where a callus is a pre-ulcer marker (see Management).

Testing for equinus. Equinus drives global forefoot overload and gastrocnemius recession is the operation that addresses it, but the contracture has to be demonstrated first and distinguished from a tight whole triceps surae. The Silfverskiöld test does this. Measure passive ankle dorsiflexion with the knee extended, then repeat with the knee flexed to 90 degrees, keeping the hindfoot in slight inversion so that the movement is true ankle dorsiflexion rather than midfoot break.

Because gastrocnemius crosses the knee and soleus does not, flexing the knee slackens gastrocnemius alone:

Dorsiflexion improves markedly with the knee flexed. An isolated gastrocnemius contracture, treated by a gastrocnemius recession.
Dorsiflexion stays limited in both positions. The whole gastrocsoleus complex is tight and a gastrocnemius recession alone will not correct it. A tendo-Achilles lengthening is the corresponding procedure, with a higher risk of over-lengthening and calcaneus gait.

The contracture and its management are developed in Gastrocnemius Equinus Contracture.

Imaging. Weight-bearing radiographs help identify a prominent or plantarflexed metatarsal, a long metatarsal or a prominent fibular condyle when planning surgery. Cross-sectional imaging is reserved for an atypical lesion, or for when a specific deep bony prominence must be proved before surgery. Thermography demonstrates the load-related footprint but is not needed for routine diagnosis.

Sketch and sagittal ultrasound of a hallux plantar keratosis over an interphalangeal ossicle, with an adventitial bursa marked on the sketch — (a) Sketch and (b) sagittal ultrasound of the hallux. The IPK lies in the plantar skin over the interphalangeal ossicle (IO), between the proximal (PP) and distal (DP) phalanges, with the flexor hallucis longus tendon (FHLT) between them; the sketch also marks an adventitial bursa (B) and the plantar plate (*).Credit: Moroni S et al. (PMC8938480) — CC BY 4.0

Clinical and thermographic images of a brown, thickened plantar callus showing lower surface temperature than adjacent skin — Clinical (left) and thermographic (right) views of a plantar callus, a brown, thickened pressure lesion. Points Sp1 and Sp3 lie on callus and Sp2 on adjacent skin; the callus reads cooler than the adjacent skin (scale 20.1 to 25.3 °C). The keratin layer alters heat transfer.Credit: Sadrzadeh-Afsharazar F et al. (PMC10708640) — CC BY 4.0

Management

Conservative care comes first. Effective treatment redistributes load across the whole contact area.

Regular paring and debridement, which temporarily reduces the bulk but does not correct the mechanical driver
Padding and offloading with a metatarsal dome or bar and accommodative orthoses
Cushioned, wide, low-heeled footwear
Emollients and keratolytics (urea, salicylic acid)
Non-operative treatment of the underlying deformity

Where the metatarsal pad goes. An offloading pad only works if it is positioned correctly, and the commonest reason one fails is that it has been put in the wrong place. The pad sits just proximal to the metatarsal heads, not under them, to support the necks and shafts so that load is taken behind the heads and the transverse arch is lifted, which lowers the pressure at the head itself. A pad placed directly beneath the painful head raises the very prominence that is causing the keratosis and makes the symptoms worse.

Check it on the patient. Do not trust the pad's printed outline. With the pad in place, the palpable metatarsal heads should sit just distal to its leading edge.

The rest of the prescription.

A stiff or rocker sole limits dorsiflexion at the metatarsophalangeal joints and shortens the time the forefoot spends loaded at push-off, often more effective than anything placed inside the shoe.
A wide, deep toe box for a clawed or hammered toe with a dorsal corn, so the shoe stops rubbing the prominence.
For a soft corn, keep the web dry and separate the toes with a soft silicone sleeve or interdigital spacer.
Accommodative rather than corrective materials in the insensate foot. The aim is to spread load and cushion, not to hold a rigid correction against skin that cannot report pain.

Full detail of the devices is in Foot & Ankle Orthotics.

Plantar strain (S_MAG) and pressure (MPP) maps for five participants, P01 to P05, under callus and control conditions — Strain (S_MAG) and pressure (MPP) maps for five participants, P01 to P05, one per row, under callus and control conditions. The paired maps show that callus changes both local strain and pressure distribution rather than acting as a passive surface thickening.Credit: Sairally F et al. (PMC13264451) — CC BY 4.0

The diabetic or neuropathic foot. Here a plantar callus is a pre-ulcerative sign: the high pressure under it causes underlying tissue breakdown and ulceration, and patients themselves often fail to notice these lesions. Regular professional debridement and immediate pressure offloading are there to stop the callus progressing to ulceration, as part of multidisciplinary diabetic-foot care.

Four-phase diagram of diabetic foot ulcer formation: neuropathy and microtrauma, ischaemia and early tissue breakdown, ulceration, then infection and chronicity — The four printed phases of diabetic foot ulceration: neuropathy and microtrauma (loss of sensation, repetitive pressure or trauma unnoticed); ischaemia and early tissue breakdown; ulceration; and infection and chronicity, with pus, osteomyelitis and risk of amputation. No callus is drawn; the callus matters because the pressure beneath it drives this breakdown.Credit: Chavan A et al. (PMC12648728) — CC BY 4.0

Surgery. Surgery is reserved for a refractory IPK or corn, and its aim is to relieve the focal pressure. Whether the IPK is discrete or diffuse decides which operation (see above).

DuVries condylectomy excises the prominent fibular (plantar) condyle of the metatarsal head under a discrete IPK.
Metatarsal osteotomy (distal, BRT or Weil-type, for example) elevates or shortens a plantarflexed or long metatarsal.
Correcting the deformity that drives a corn: hammer or claw toe correction, condylectomy of a phalangeal condyle for a soft corn, or hallux valgus correction.

Plantar prominence of the ball of the hallux with radiographs after a proximal and dorsal first metatarsal-head sliding osteotomy fixed with wires — (A) Plantar prominence of the ball of the hallux beneath the first metatarsal head (arrowhead). (B, C) Radiographs after a sliding osteotomy that shifts the metatarsal head proximally and dorsally, fixed with wires, preserving the sesamoids. Elevate only enough to unload the lesion; excessive elevation creates first-ray insufficiency and transfer pressure.Credit: Nakajima K et al. (PMC12608295) — CC BY 4.0

Dorsal foot dissection marking percutaneous incision sites, bone model of a distal metatarsal osteotomy at the neck, and a lateral radiograph marking the osteotomy sites — Distal metatarsal metaphyseal osteotomy. (A) Dorsal dissection with the percutaneous incision points marked in blue, away from the loaded plantar skin. (B) Bone model: the cut at the level of the metatarsal neck, then the head after shortening and elevation (red arrow). (C) Lateral radiograph with arrows at the osteotomy sites. The cut permits controlled shortening and elevation of an overloaded central ray while preserving the plantar soft-tissue envelope.Credit: Biz C et al. (PMC6276525) — CC BY 4.0

Clinical photographs of a callus-surrounded submetatarsal ulcer healing over time, and pedobarographs before and after floating metatarsal osteotomy — (A) A callus-surrounded submetatarsal diabetic ulcer; (B, C) healing after floating osteotomy; (D, E) pedobarographs before and after, with a marked fall in peak pressure beneath the second metatarsal. Reassess the adjacent heads: pressure reduction under one ray can become a transfer lesion under another.Credit: Tamir E et al. (PMC8127671) — CC BY 4.0

Approach from the dorsum, not through the sole. Every one of these operations is reached through a dorsal incision, because a scar on weight-bearing plantar skin can be more painful and more disabling than the keratosis it was meant to cure. Plantar skin is thick, tethered by fibrous septa to the fat pad beneath it, and takes load with every step. An incision there heals into a firm, tender scar that becomes a focal prominence in its own right, and the patient trades a callus for something that cannot be offloaded.

Perform the condylectomy or osteotomy through a dorsal or dorsolateral incision over the relevant metatarsal or web space, working down to the plantar condyle from above.
Do not excise the keratosis. The skin is the symptom: removing it leaves a wound in a high-pressure area, and the lesion recurs unchanged unless the bony cause is addressed.
If a plantar incision is genuinely unavoidable, place it longitudinally and away from the loaded metatarsal heads and heel, in the relatively unloaded arch.
The same logic is sharper in the diabetic foot, where a plantar wound in an insensate, poorly perfused ray is how an elective procedure becomes an ulcer.

Beware Transfer Lesions

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. It may also precipitate a hammer toe of the operated ray. In one long-term series of distal metatarsal osteotomies for intractable plantar callosity, most callosities healed, but 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 or diabetic patients.

Mnemonics & Memory Aids

Mnemonic

LINES

Lines (skin) run THROUGH an IPK/callus (interrupted by a verruca)

IPK is over a bony point (met head)

No bleeding on paring (verruca = pinpoint bleeding)

Even/direct pressure hurts an IPK (pinch hurts a verruca)

Stratum corneum keratin only (verruca = thrombosed capillaries)

Hook:Skin LINES through it + direct-pressure pain + no bleeding = IPK, not a verruca.

Mnemonic

PADS

Pare/debride regularly

Accommodate - orthoses, met dome/bar, footwear (offload)

Deformity - correct the cause (toes/metatarsal)

Surgery (condylectomy/osteotomy) last - beware transfer lesions

Hook:Treat with PADS - offload first, surgery (with transfer-lesion caution) last.

Clinical Decision Scenarios

Practise clinical reasoning and management decisions out loud

Viva scenarioStandard

Clinical prompt

“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?”

Viva scenarioStandard

Clinical prompt

“Why does a plantar callus matter more in a patient with diabetes, and how does that change your management?”

Exam day cheat sheet

Plantar Keratotic Disorders - Exam Day Cheat Sheet

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

Evidence & Key Studies

Evidence

Straight (transverse distal) metatarsal osteotomy for the treatment of plantar callosities

Kiviniemi VJ, Leppilahti J, Jalovaara P • Annales Chirurgiae et Gynaecologiae (2000)

Key Findings:

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.

Limitation: TWENTY-FIVE CALLOSITIES IN THIRTEEN PATIENTS, NO CONTROL GROUP, AND THE LEARNING IS IN THE FAILURE MODE - 23 of 25 healed, but eight hammer toes developed in the operated rays and eight NEW callosities under adjacent rays, so the operation redistributes load rather than removing the reason for it. That is the transferable lesson and the counselling point. Multiple callosities per foot mean the 25 observations are not independent. Seven years is a genuine strength - most foot-surgery series stop at two - and it is exactly the duration that exposed the transfer lesions, which a short series would have missed. Single centre, retrospective, and 'intractable' is defined by referral rather than by any stated conservative protocol.

Verify on PubMed (PMID 11204964)

Evidence

Differences between patient-reported and clinician-observed nonulcerative foot signs in diabetes

III

Takehara K, Oe M, Ohashi Y, et al. • Journal of Wound, Ostomy and Continence Nursing (2019)

Key Findings:

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.

Limitation: A CROSS-SECTIONAL OBSERVATION STUDY IN A DIABETIC COHORT, AND THE SENSITIVITY FIGURES ARE OF PATIENTS DETECTING THEIR OWN LESIONS - 51% for calluses and 44% for corns measure self-awareness, not the prevalence or the danger of the lesions, so nothing here quantifies how risky a callus is, only that patients miss them. The clinical upshot - professional surveillance matters because patients do not see these lesions - is sound and is the reason this card is here, but it is an argument FOR surveillance, not evidence that surveillance prevents ulcers: no ulcer outcome was measured. Self-report against clinician observation at one point in time, single cohort, and nothing here transfers to a non-diabetic foot.

Verify on PubMed (PMID 30747799)

Evidence Attribution

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, as are the metatarsal-pad position, the Silfverskiold test and the dorsal-approach principle. (See also Metatarsalgia, Lesser Toe Deformities, Claw Toes, Diabetic Foot, Gastrocnemius Equinus Contracture and Foot & Ankle Orthotics.)

IPK or callus

Verruca (plantar wart)

Site

Over a weight-bearing bony point (metatarsal head)

Anywhere on the sole

Skin lines (dermatoglyphics)

Run through the lesion

Interrupted

Tenderness

To direct pressure

To lateral pinch or squeeze

On paring

Keratin only, no bleeding

Pinpoint bleeding from thrombosed capillaries (black dots)

Conservative care comes first. Effective treatment redistributes load across the whole contact area.

Regular paring and debridement, which temporarily reduces the bulk but does not correct the mechanical driver
Padding and offloading with a metatarsal dome or bar and accommodative orthoses
Cushioned, wide, low-heeled footwear
Emollients and keratolytics (urea, salicylic acid)
Non-operative treatment of the underlying deformity

Check it on the patient. Do not trust the pad's printed outline. With the pad in place, the palpable metatarsal heads should sit just distal to its leading edge.

The rest of the prescription.

A stiff or rocker sole limits dorsiflexion at the metatarsophalangeal joints and shortens the time the forefoot spends loaded at push-off, often more effective than anything placed inside the shoe.
A wide, deep toe box for a clawed or hammered toe with a dorsal corn, so the shoe stops rubbing the prominence.
For a soft corn, keep the web dry and separate the toes with a soft silicone sleeve or interdigital spacer.
Accommodative rather than corrective materials in the insensate foot. The aim is to spread load and cushion, not to hold a rigid correction against skin that cannot report pain.

Full detail of the devices is in Foot & Ankle Orthotics.

Surgery. Surgery is reserved for a refractory IPK or corn, and its aim is to relieve the focal pressure. Whether the IPK is discrete or diffuse decides which operation (see above).

DuVries condylectomy excises the prominent fibular (plantar) condyle of the metatarsal head under a discrete IPK.
Metatarsal osteotomy (distal, BRT or Weil-type, for example) elevates or shortens a plantarflexed or long metatarsal.
Correcting the deformity that drives a corn: hammer or claw toe correction, condylectomy of a phalangeal condyle for a soft corn, or hallux valgus correction.

Perform the condylectomy or osteotomy through a dorsal or dorsolateral incision over the relevant metatarsal or web space, working down to the plantar condyle from above.
Do not excise the keratosis. The skin is the symptom: removing it leaves a wound in a high-pressure area, and the lesion recurs unchanged unless the bony cause is addressed.
If a plantar incision is genuinely unavoidable, place it longitudinally and away from the loaded metatarsal heads and heel, in the relatively unloaded arch.
The same logic is sharper in the diabetic foot, where a plantar wound in an insensate, poorly perfused ray is how an elective procedure becomes an ulcer.

Beware Transfer Lesions