Corns

Aka: Corns, Plantar Keratosis, Plantar Callus, Clavus, Clavus durus, Clavus mollis, Heloma durum, Heloma molle

1. Pathophysiology
   1. Stage I: Chronic intermittent irritation or pressure
      1. See Causes below
   2. Stage II: Callus formation
      1. Initial vasodilation
      2. Increased corneum production
      3. Epidermal thickening occurs (hyperkeratosis)
   3. Stage III: Corn formation
      1. Localized callus forms hyperkeratotic Nodule (corn)
2. Causes
   1. Due to excessive pressure or focal irritation
      1. Excessive pronation
         1. Results in Hammertoe deformity
         2. Excessive pressure on Metatarsal heads
      2. Tight shoes or otherwise poorly fitting shoes
      3. Hammertoe deformity (common cause)
      4. Excessive supination
         1. Highly arched foot (longitudinal arch)
      5. Strength imbalance of peroneal and tibial muscles
   2. Secondary causes
      1. Plantar Wart
      2. Foreign body granuloma
      3. Porokeratosis plantaris discreta
3. Types
   1. Plantar Keratosis (Clavus or Corn)
      1. Hyperkeratotic Nodule on sole of foot
      2. Often located over third Metatarsal head
   2. Hard Corn (Clavus durus or Heloma durum)
      1. Most common type of corn
      2. Firm keratin Nodule in pressure areas
         1. Well circumscribed
         2. Central conical keratin core
      3. Sites
         1. Dorsolateral aspect of fifth toe
         2. Dorsum of interphalangeal joints of lateral toes
   3. Soft Corn (Clavus mollis or Heloma molle)
      1. Macerated corn due to perspiration
      2. Extremely tender
      3. Sites
         1. Occurs between toes
         2. Often located between fourth and fifth toes
4. Signs
   1. Hyperkeratotic Nodule in pressure area of foot
   2. Tender to direct palpation
   3. Paring lesion reveals clear, hard keratin center
5. Differential Diagnosis
   1. Tinea Pedis
      1. Contrast with interdigital soft corn
   2. Plantar Wart
      1. Contrast with hard corn
      2. Plantar Warts bleed when shaved
      3. Plantar Warts are tender to lateral compression
      4. Plantar Warts have black dots (thrombosed vessels)
6. Management
   1. Manage underlying foot deformities if present
      1. See Hammertoe
      2. Correct over-pronation if present
   2. Keratin removal
      1. Physician or Podiatrist
         1. Paring with sterile blade (15 blade)
         2. Curettage of keratin core
      2. Home treatment
         1. Warm water soak followed by pumice stone
         2. Corn Plaster (felt pad with 40% salicylic acid)
            1. Avoid contact with normal skin
            2. Avoid in patients with Neuropathy
   3. Padding to reduce mechanical irritation
      1. Pads for hard corns
         1. Silicone toe sleeves (releases Mineral Oil)
         2. Foam padding
      2. Pads for soft corns (applied to web space)
         1. Lamb's Wool padding
         2. Foam toe spacer
      3. Other pads
         1. Polymer gel (e.g. Cushlin Gel)
   4. Relieve pressure on affected area of foot
      1. Metatarsal pad in shoe for Plantar Keratosis
         1. Mark most tender area (e.g. third Metatarsal head)
            1. Grease pencil
            2. Lipstick
         2. Step into shoe barefoot
         3. Note mark left in shoe insole
         4. Apply Metatarsal pad proximal to mark in shoe
         5. Adhesive felt (1/8 to 1/4 inch thick)
      2. Shoe modification
         1. Purchase shoe with large, deep toe box
         2. Low healed shoe
         3. Soft upper portion of shoe
         4. Check shoe for irregularities that cause pressure
7. Management: Surgery
   1. Indicated for corns refractory to conservative therapy
   2. Correctable abnormalities
      1. Hammertoe, Claw toe, or mallet toe deformity
      2. Fifth toe hard corn resection
8. References
   1. Lebowitz in Barker (1995) Ambulatory Care, p. 1497-9
   2. Bedinghaus (2001) Am Fam Physician 64:791-804
   3. Freeman (2002) Am Fam Physician 65(11): 2277-80