Diagnostic Approach for Diabetic Plantar Foot Ulcer

Primary Concern: Ruling Out Osteomyelitis

• The American Diabetes Association recommends performing probe-to-bone testing at the bedside by inserting a sterile metal probe into the ulcer base to assess for osteomyelitis, which has high sensitivity and specificity for underlying osteomyelitis and mandates further investigation 1
• Weight-bearing plain radiographs of the affected foot should be ordered to evaluate for bone destruction, periosteal reaction, or architectural changes consistent with osteomyelitis or Charcot arthropathy, as approximately 20% of infected diabetic foot ulcers have bone involvement 1

Secondary Priority: Vascular Assessment

• The American College of Cardiology recommends measuring toe pressure or transcutaneous oxygen pressure (TcPO2) as the most reliable bedside tests for predicting healing potential in diabetic patients with neuropathy, with values ≥30 mmHg or ≥25 mmHg increasing the probability of healing by at least 25% 2, 3
• Ankle-brachial index (ABI) is unreliable in diabetic patients with neuropathy due to medial arterial calcification, making toe pressure or TcPO2 the preferred tests, with pedal Doppler waveform analysis providing strong evidence against significant peripheral artery disease 2, 3, 5

Clinical Context and Pitfalls

• The presence of central erythema with signs of healing raises concern for infection masquerading as healing tissue, and erythema extending beyond the wound margin (>2 cm) indicates infection, not healing 1
• Never delay objective vascular testing based on palpable pulses alone, as up to 50% of diabetic foot ulcers have coexisting peripheral artery disease, and even experienced clinicians can detect pulses despite significant ischemia 2, 3, 5