What are foot ulcers?

Definition and Pathophysiology of Foot Ulcers

Foot ulcers are open sores or wounds on the foot that occur most commonly in people with diabetes, characterized by a break in the protective cutaneous envelope, typically at sites of trauma or pressure, and are associated with high morbidity, mortality, and significant financial costs. 1, 2

Characteristics and Epidemiology

• Foot ulceration is a major complication of diabetes mellitus with a lifetime incidence rate of 19-34% and a yearly incidence rate of approximately 2% 1
• After successful healing, recurrence rates are alarmingly high at 40% within one year and 65% within three years 1
• Foot ulcers often precede lower-extremity amputation, with 14-24% of diabetic foot ulcers requiring amputation due to bone infection or other complications 3

Primary Pathophysiological Mechanisms

• Three main pathological mechanisms underlie foot ulcer development: 2, 3

  1. Neuropathy (sensory, motor, and autonomic)
  2. Vascular insufficiency (peripheral arterial disease)
  3. Secondary infection following trauma

• Diabetic peripheral neuropathy plays a central role in ulcer development: 2

  • Sensory neuropathy leads to loss of protective sensation (LOPS), allowing minor trauma to go unnoticed
  • Motor neuropathy contributes to foot deformities (claw toes, hammer toes), creating areas of high pressure
  • Autonomic neuropathy reduces sweating, leading to dry skin prone to cracking

• Peripheral arterial disease (PAD) is present in up to 50% of patients with diabetic foot ulcers, acting as a significant risk factor for impaired wound healing and amputation 2

Types and Classification

Foot ulcers can be classified by etiology as: 1

• Neuropathic - occur on the plantar surface or areas overlying bony deformities
• Ischemic - more common on toe tips or lateral foot borders
• Neuro-ischemic - combination of both mechanisms

Risk Factors

The International Working Group on the Diabetic Foot (IWGDF) identifies key risk factors: 1

• Loss of protective sensation (LOPS)
• Peripheral artery disease (PAD)
• Foot deformities
• History of previous foot ulceration or amputation
• End-stage renal disease

Pre-Ulcerative Signs

Pre-ulcerative signs that may lead to foot ulceration include: 1

• Abundant callus formation
• Blisters
• Ingrown or thickened nails
• Fungal infections
• Dry, cracked skin

Biomechanical Factors

• Abnormal biomechanical loading of the foot results from loss of sensation, foot deformities, and limited joint mobility 2
• High-pressure areas develop, leading to callus formation which further increases abnormal loading 2
• Ill-fitting shoes and walking barefoot with insensitive feet are frequent causes of ulceration, even in patients with purely ischemic ulcers 1

Progression and Complications

• If not properly diagnosed and treated, foot ulcers tend to progress rapidly 2
• Infection can spread contiguously to subcutaneous tissues, fascia, tendons, muscles, joints, and bones 2
• The combination of infection with PAD significantly increases the risk of amputation 2

Risk Stratification

The IWGDF categorizes ulcer risk into four levels: 1

• Very low risk (Category 0): No LOPS and No PAD
• Low risk (Category 1): LOPS or PAD
• Moderate risk (Category 2): LOPS + PAD, or LOPS + foot deformity, or PAD + foot deformity
• High risk (Category 3): LOPS or PAD plus history of foot ulcer, lower-extremity amputation, or end-stage renal disease

Understanding the pathophysiology and risk factors of foot ulcers is essential for early identification, appropriate management, and prevention of this devastating complication that significantly impacts morbidity, mortality, and quality of life.