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Difficulty: MediumOrdering Imaging Studies

A 58-year-old man with a 15-year history of type 2 diabetes mellitus and peripheral neuropathy presents to his primary care physician for evaluation of a malodorous wound on the bottom of his right foot. He first noticed the ulcer three weeks ago and reports that the drainage has increased over the past several days. He denies fever, chills, or night sweats. Current medications include metformin, empagliflozin, and atorvastatin. Vital signs show a temperature of 37.1°C (98.8°F), blood pressure of 134/82 mmHg, heart rate of 78/min, and respiratory rate of 14/min. Physical examination reveals a 2.5 cm by 2.0 cm deep ulceration underlying the first metatarsal head. There is surrounding erythema, induration, and purulent discharge. A sterile metal probe introduced into the ulcer easily palpates hard, gritty tissue at the base. Dorsalis pedis and posterior tibial pulses are slightly diminished bilaterally, and monofilament testing reveals loss of protective sensation in bilateral feet. Laboratory studies reveal a leukocyte count of 11,800/mm³ and an erythrocyte sedimentation rate of 88 mm/h. Which of the following is the most appropriate initial imaging study for this patient?

  1. Plain radiography of the right footAnswer
  2. B
    Magnetic resonance imaging of the right foot
  3. C
    Computed tomography of the right foot
  4. D
    Three-phase technetium-99m bone scintigraphy
  5. E
    Lower extremity arterial duplex ultrasonography

Answer

Plain radiography of the right foot
The correct answer is plain radiography. This patient's deep ulcer, elevated ESR, and positive probe-to-bone test strongly suggest underlying osteomyelitis. According to established clinical guidelines, plain radiography is the most appropriate initial imaging study for suspected osteomyelitis. Even though radiographic evidence of bone destruction (e.g., periosteal elevation, cortical erosion) may take up to 2 weeks to appear, plain films are cost-effective, rapidly available, provide a necessary baseline for future comparison, and help exclude other diagnoses such as fractures, foreign bodies, or gas-forming infections.

Step-by-Step Solution

1
Identify the primary clinical problem from the presentation.
The patient has a deep diabetic foot ulcer with a positive probe-to-bone test and an elevated erythrocyte sedimentation rate (ESR).
A positive probe-to-bone test in a diabetic foot ulcer is highly predictive of underlying osteomyelitis, making it the most critical condition to evaluate.
2
Determine the standard diagnostic pathway for suspected osteomyelitis.
Guidelines recommend plain radiography as the initial imaging modality.
Although plain radiography has lower sensitivity for early osteomyelitis, it is rapid, cost-effective, establishes a baseline, and can identify alternative diagnoses or complications like gas in soft tissues, foreign bodies, or gross bony destruction.
3
Evaluate the distractors based on test sequencing and appropriateness.
Advanced imaging like MRI or bone scans should be reserved for when initial plain films are negative or inconclusive despite high clinical suspicion.
Ordering advanced imaging initially violates standard step-wise, value-based diagnostic protocols.

Key Concept

In suspected diabetic foot osteomyelitis (indicated by a positive probe-to-bone test), plain radiography is always the initial imaging study of choice.
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Ordering Imaging Studies

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