Corns and callosities (syn. calluses)

Inappropriate shoes, abnormal foot mechanics, and high levels of activity produce pressure and friction that lead to corns and callosities. Most lesions can be managed conservatively by proper footwear, orthoses, and, if necessary, regular paring. The lesions usually disappear when the causative mechanical forces are removed. Surgery is rarely indicated and should be specifically aimed at correcting the abnormal mechanical stresses.

This chapter is set out as follows:

Many factors contribute to the development of corns and callosities.

• Inappropriate shoes
  • Callosities on the edges of the weight-bearing feet are often caused by shoes that are too loose
  • Soft corns tend to arise from wearing tight shoes
     
• Abnormal foot mechanics
  • Elderly patients
  • Hallux valgus
  • Diabetic neuropathy
  • Rheumatoid arthritis
     
• High levels of activity produce pressure and friction

• Lesions can be painful, especially corns and soft corns

Definitions

• A callosity (syn. callus) is a plaque of thickened skin
• A corn is a sharply demarcated callosity, which has developed a central, and often painful, keratin core
• A soft corn occurs between the toes 

Distribution

• Corns and callosities
• Can occur on any bony surface, most frequently the hands and feet
• Feet - common sites include over metatarsal heads and the heel on the plantar foot, prominent interphalangeal joints on the dorsal foot, and the ends of the toes
• Hands - palms and over the metacarpophalangeal joints, and are often job-specific

• Soft corn
• The most common site is between the fourth and fifth toes

Morphology

• The main differential is that of warts
  • Callosities have skin markings
  • Direct pressure generally causes tenderness in corns and callosities, whereas warts are tender with pressure applied from side to side
  • After paring the skin, callosities have a waxy appearance, corns have a central keratin plug, and warts have black thrombosed capillaries

Step 1: general measures

• Advise on well-fitting, comfortable, flat footwear
• Depending on the site of the lesion, a cushioning pad or shoe insole may be of benefit. For example, a soft shoe inlay may aid a callosity or corn under the foot, whereas a corn plaster / other toe separator may help a soft corn between the toes

Step 2: reduce skin thickness

• Pare down the thickening with a pumice stone or emery paper once to twice a week
• Before paring it is best to soften the skin by soaking the affected area in warm water for 10-20 minutes. Additionally, a moisturising cream used regularly will keep the skin softened and easier to pare
• In cases of very thick skin, including corns where there is often a deeper central keratin core, a trained health professional may be needed in the first instance to remove the majority of the keratin with a scalpel blade 

Step 3: medical treatment

• Creams containing salicylic acid or urea may help reduce skin thickness
• Many over the counter wart preparations contain salicylic acid, however, such treatments should be avoided in diabetic patients

Step 4: referral

• For persistent lesions and / or high-risk individuals, eg diabetics, patients will need referring to a podiatrist for further management
• Occasionally surgical correction, by a podiatric surgeon or orthopaedic surgeon, is needed to correct an underlying bony deformity