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Difficulty: MediumOrdering Imaging Studies

A 61-year-old man presents to the outpatient clinic for the evaluation of a right foot wound. He has a 15-year history of poorly controlled type 2 diabetes mellitus, hypertension, and severe peripheral neuropathy. The patient states he first noticed a painless sore on the bottom of his right big toe approximately two weeks ago. He has experienced no fevers, chills, or systemic symptoms. Vital signs are within normal limits. Physical examination reveals a 1.5-cm, deep ulceration on the plantar aspect of the right first metatarsophalangeal joint. There is a 2-mm rim of surrounding erythema, but no fluctuance or purulent drainage is noted. During the examination, a sterile metal probe is inserted into the ulcer and touches hard, gritty tissue at the base of the wound. Laboratory studies show a leukocyte count of 8,500/mm38,500/mm^3 and an erythrocyte sedimentation rate of 68 mm/h68 \text{ mm/h}. Which of the following is the most appropriate initial imaging study to order for this patient?

  1. Plain radiography of the right footAnswer
  2. B
    Magnetic resonance imaging of the right foot without contrast
  3. C
    Three-phase technetium-99m bone scintigraphy
  4. D
    Computed tomography of the right foot
  5. E
    Duplex ultrasonography of the lower extremity arteries

Answer

Plain radiography of the right foot
The correct answer is plain radiography. In any patient with a diabetic foot ulcer and a high suspicion for osteomyelitis (strongly suggested here by the positive probe-to-bone test and elevated erythrocyte sedimentation rate), plain radiography of the foot is the mandatory initial imaging study. Although it has low sensitivity for acute osteomyelitis (often requiring 10-14 days for cortical destruction or periosteal reaction to become visible), it is highly cost-effective, easily accessible, and essential for ruling out other causes of foot pain or deformity, such as Charcot arthropathy, soft tissue gas, or radio-opaque foreign bodies.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and physical examination findings.
The patient has a deep diabetic foot ulcer with a positive probe-to-bone test and an elevated erythrocyte sedimentation rate.
Identifying these key features raises the clinical suspicion for contiguous osteomyelitis.
2
Determine the standard diagnostic sequencing for the suspected condition.
Guidelines dictate that all patients with suspected osteomyelitis should initially undergo plain radiography of the affected area.
Plain films are inexpensive, readily available, and can identify alternative diagnoses or severe bone destruction, serving as a baseline before advancing to more expensive imaging.
3
Evaluate the roles of advanced imaging modalities.
Advanced imaging (like magnetic resonance imaging) is deferred unless initial radiographs are negative or surgical intervention is being planned.
To prevent the overutilization of healthcare resources and adhere to correct step-wise diagnostic protocols.

Key Concept

In patients with suspected osteomyelitis (e.g., a diabetic foot ulcer with a positive probe-to-bone test), plain radiography is always the most appropriate initial imaging study.
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Topics

Ordering Imaging Studies

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