Diabetic foot

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Diabetic Foot

Overview

Diabetic foot disease is one of the most serious complications of diabetes mellitus, accounting for approximately 20% of all diabetic hospitalizations. The annual incidence of foot complications is 1-2% per year. About 1 in 4 patients with diabetes will develop a foot complication during their lifetime, and 15-20% of diabetic foot ulcers (DFUs) result in lower extremity amputation (LEA). Approximately 85% of all lower extremity amputations are preceded by a DFU.

Current Surgical Therapy 14e, p. 1186
Bailey and Love's Short Practice of Surgery 28th Ed, p. 628

Pathophysiology: The Triad

DFUs are multifactorial, driven by a triad of three interacting mechanisms:

1. Peripheral Neuropathy

Sensory neuropathy: Loss of protective sensation (LOPS) - patients don't notice pressure, heat, or small wounds
Motor neuropathy: Muscle atrophy causing structural deformity (claw toe, hammertoe), which creates abnormal pressure points
Autonomic neuropathy: Decreased sweating → dry skin → cracks, fissures, and ulceration

The most common cause of injury is pressure on plantar bony prominences. Sensory loss is assessed with a 10-g monofilament plus at least one other modality (pinprick, temperature, vibration, or proprioception).

2. Ischemia / Peripheral Arterial Disease (PAD)

Macro-vascular: large-vessel atherosclerosis - diabetics are prone to medial calcinosis ("lead-pipe" calcification), making ABI unreliable
Micro-vascular: impaired tissue perfusion and impaired healing
PAD worsens both ulcer healing and post-operative wound closure

3. Infection

Begins as bacterial invasion into compromised tissue
Rapidly spreads to deep structures including bone (osteomyelitis)
Immune defects and hyperglycemia further impair the response

Altered foot mechanics (Charcot foot) from repeated undetected fractures can destroy normal foot architecture completely.

Goldman-Cecil Medicine, p. 1425

Classification Systems

WIfI Classification (Wound, Ischemia, foot Infection)

Developed by the Society for Vascular Surgery, this is now the preferred system. Each domain is graded 0-3 (none to severe), giving 64 permutations that predict:

Risk of major LEA at 1 year
Theoretical benefit of revascularization

WIfI grade also correlates with wound healing time and 1-year amputation-free survival.

Wound Grades (WIfI)

Grade	Description
0	No wound / pre-ulceration
1	Shallow ulcer, no exposed bone (except distal phalanx), no gangrene
2	Ulcer with exposed bone, digit gangrene, or shallow heel ulcer
3	Extensive ulcer/gangrene, full-thickness heel ulcer

Other Systems

Wagner Classification - widely used but does not account for ischemia fully
University of Texas Classification - grades wound depth + infection + ischemia
SINBAD Score - used in epidemiological comparisons
Current Surgical Therapy 14e, p. 1186

Clinical Presentation

Ulceration typically on the plantar surface under metatarsal heads, or the calcaneum, surrounded by callus
Spreading cellulitis, fevers, or critical ischemia indicate severe infection
Signs of local inflammation: erythema, warmth, swelling, crepitation (gas in tissues)
Patients may be asymptomatic due to neuropathy - infection can fester for weeks undetected

Severe diabetic foot infection showing marked infection, necrosis, and tissue loss

Severe diabetic foot infection with marked infection, necrosis and tissue loss. This neuropathic foot with ankle/hindfoot deformity was salvaged with corrective triple fusion, excision of infected ulcer, antibiotics, and primary closure. (Bailey & Love's, Fig. 43.11)

Investigations

Investigation	Finding / Role
Blood tests	Often unhelpful - inflammatory markers may be normal or only mildly raised
Plain X-ray (3-view)	First-line; may show osteomyelitis (can be normal early), gas in soft tissue, foreign bodies, Charcot deformity
MRI	Most sensitive modality for bone involvement / osteomyelitis
Probe-to-bone test	Combined with elevated CRP and abnormal X-ray confirms osteomyelitis
Wound swabs	Superficial swabs are unreliable for deep infection pathogens
Bone biopsy	Gold standard for culture in complex/severe infection
ABI / Toe pressures	Assess for PAD; ABI may be falsely elevated due to calcification - use toe-brachial index or TcPO2 instead

Bailey and Love's 28th Ed, p. 628
Current Surgical Therapy 14e, p. 1186

Microbiology

Mild infections: Gram-positive cocci - S. aureus, beta-haemolytic streptococci
Moderate-severe infections: Polymicrobial - aerobic Gram-positives + Gram-negative bacilli + anaerobes
Pseudomonas aeruginosa is over-represented; empiric therapy for severe infections must include Pseudomonas coverage
Anaerobes: Consider metronidazole especially for abscesses and devitalized tissue
Ulcer swabs/sinus tract cultures are not reliable - they do not reflect deep pathogen burden
Bailey and Love's 28th Ed, p. 628

Management

1. Antibiotic Therapy

Severity	Treatment
Mild	Oral: TMP-SMX 800/160 mg BD, or clindamycin 300 mg QID, or cephalexin 500 mg QID
Moderate-Severe	IV: Piperacillin-tazobactam 3.375 g IV q8h + vancomycin 15 mg/kg IV q12h

Tissue culture (surgical) should guide definitive therapy. Osteomyelitis typically requires 4-6 weeks of antibiotics (even with disease-free margins at resection, based on practical experience).

2. Wound Care

Debridement: Callus debridement first to assess wound depth; surgical debridement for collections, necrotic areas, or osteomyelitis
Pressure off-loading: Total-contact casts, special shoes, orthotics - essential for plantar ulcer healing
Strict non-weight-bearing regimen
Advanced wound dressings with healing accelerators
Negative-pressure wound therapy (NPWT) - evidence from recent meta-analysis (PMID 39241769) supports efficacy in DFUs

3. Surgical Intervention

Drainage of abscesses
Debridement of devitalized tissue
Ray amputation (partial or full) for infected toes/metatarsals
Wound closure is staged - infected wounds left open initially
For wounds with exposed tendon/bone or unable to close: Integra dermal regeneration template, followed by split-thickness skin grafting (12-month healing rate ~79%, 18-month ~93%)
Amputation - not a simple option; wound healing is unpredictable; ensure all infected material is excised with tension-free closure

4. Revascularization

Mandatory vascular assessment in all patients with poor peripheral pulses
Angioplasty or bypass surgery for PAD to improve distal vascularity before or alongside foot surgery
WIfI classification predicts the benefit of revascularization

5. Glycemic Control

Tight glycemic control important for healing
HbA1c ≤8% (rather than the traditional ≤7%) has been shown to be sufficient for avoiding major amputation in patients with DFUs
Endocrinology should be integrated into the multidisciplinary team

6. Other Adjuncts

Hyperbaric oxygen - some evidence for complicated infections, particularly anaerobic
Bioengineered skin substitutes
Autologous leukocytes and platelet-rich plasma for non-healing ulcers
Smart wearable technology - emerging role in prevention and monitoring (systematic review, PMID 40682082)
Rosen's Emergency Medicine, p. 2540
Goldman-Cecil Medicine, p. 1425-1426

Osteomyelitis in Diabetic Foot

The most important risk factor for osteomyelitis is the presence of a foot ulcer. Key points:

Probe-to-bone test + elevated inflammatory markers + abnormal X-ray = confirmed diagnosis
MRI is the most sensitive investigation
Bone biopsy (surgical) is preferred over swabs for culture
Treatment: surgical resection of infected bone + prolonged antibiotics (4-6 weeks post-resection)
Distinguishing superficial osteitis (from soft tissue loss/vascular compromise) from deep osteomyelitis is important - the former may require only optimization of glycaemic control, vascular supply, and footwear

Multidisciplinary Team (MDT) Approach

MDT care is now the standard of care for diabetic foot wounds. A comprehensive MDT reduces LEA rates through early recognition and management. Core members include:

Vascular surgeon
Surgical podiatrist
Wound care specialist
Endocrinologist
Infectious disease specialist (as needed)
Plastic/orthopaedic surgery (as needed)

MDT management improves wound healing, lowers major amputation rates, reduces readmissions, and is cost-effective.

Current Surgical Therapy 14e, p. 1190

Prevention

Routine foot examination at every medical visit for patients with sensory loss
Daily self-inspection for cracks, fissures, ulcers, or inflammation
Never walk barefoot (even at home)
Wear closed protective footwear; avoid sandals outdoors
Avoid heating pads / hot water bottles on feet (thermal injury risk due to LOPS)
Refer to foot care specialist for: sensory loss, foot deformity, extensive callus, non-healing ulcers
Custom therapeutic footwear and periodic foot inspection are part of optimal DFU management
Goldman-Cecil Medicine, p. 1426

Charcot Foot (Neuropathic Arthropathy)

Altered foot mechanics from repeated undetected fractures lead to destruction of normal foot architecture - the classic Charcot foot deformity. This significantly increases susceptibility to ulceration from abnormal pressure points and is identified on plain X-ray.

Recent Evidence:

Advanced wound dressings vs standard care for DFUs: Italian guideline meta-analysis (PMID 38864979) - different advanced dressings show varied efficacy; the guideline recommends tailored selection
NPWT in DFUs: Systematic review/meta-analysis (PMID 39241769) - supports NPWT as an effective adjunct in DFU management

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