Should I obtain a plain‑film X‑ray or a CT (computed tomography) scan of a male patient’s foot with an unstageable pressure ulcer, diabetes mellitus, and a recent contralateral below‑knee amputation?

Imaging for Unstageable Pressure Ulcer in High-Risk Diabetic Foot

Start with plain X-rays immediately—they are the universally recommended first-line imaging for any diabetic foot wound, especially in this high-risk patient with diabetes, contralateral amputation, and an unstageable ulcer that likely involves underlying bone. 1, 2

Initial Imaging: Plain X-Ray First

• Obtain plain radiographs of the affected foot now as the mandatory first step for any patient with a diabetic foot wound and suspected bone involvement. 1

• Request anteroposterior (AP), medial oblique, and lateral projections to adequately visualize all osseous structures. 1

• Weight-bearing films are ideal if the patient can tolerate them, but non-weight-bearing views are acceptable given his recent contralateral BKA and likely limited mobility. 1

• Plain X-rays will detect:

  • Bone destruction, cortical erosion, periosteal reaction 1
  • Soft tissue gas (critical finding) 1
  • Radio-opaque foreign bodies 1
  • Charcot changes or fractures (common in neuropathic diabetic patients with ulcers) 3

Why X-Ray Alone May Not Be Enough

• Critical caveat: X-rays require approximately 2 weeks of bone loss to show abnormalities, making them insensitive for acute osteomyelitis. 1, 2

• An unstageable pressure ulcer (by definition, obscured by eschar or slough) carries extremely high risk for underlying osteomyelitis, especially over a bony prominence. 1

• If X-rays are negative but clinical suspicion remains high (which it should in this patient), you cannot stop there. 1

When to Proceed Directly to MRI

You should strongly consider ordering MRI immediately alongside or shortly after the initial X-ray in this patient because:

• MRI is the study of choice when osteomyelitis diagnosis remains uncertain or when defining the extent of soft tissue involvement (abscess, tenosynovitis, joint involvement). 1, 4

• MRI has sensitivity of 96.4-98% and specificity of 83.8-89% for osteomyelitis detection—far superior to plain films. 2, 4

• This patient has multiple high-risk features that increase pre-test probability of osteomyelitis:

  • Unstageable ulcer (likely large and deep) 1
  • Diabetes with neuropathy (implied by pressure ulcer formation) 1, 3
  • Recent contralateral BKA (suggests severe peripheral vascular disease and previous infection complications) 1

• MRI provides critical information X-rays cannot: extent of bone infection, soft tissue abscesses, sinus tracts, joint involvement, and precise surgical planning if debridement is needed. 1, 2

CT Scan: Not Recommended as Primary Imaging

• CT is not the preferred modality for diabetic foot osteomyelitis evaluation. 1

• CT is only mentioned as a distant alternative when MRI is unavailable or contraindicated, and even then, nuclear medicine studies (SPECT-CT, labeled WBC scans) are preferred over CT alone. 1

• CT does not provide the soft tissue contrast or marrow edema detection that MRI offers. 1, 5

Practical Algorithm for This Patient

1. Order plain X-rays immediately (AP, oblique, lateral views). 1, 2

2. Simultaneously or within 24-48 hours, order MRI given the high pre-test probability of osteomyelitis in this patient. 1, 4

3. Perform probe-to-bone test at bedside if the ulcer is open (after debridement of eschar if needed)—a positive test combined with abnormal X-rays has 97% sensitivity and 93% specificity for osteomyelitis. 1, 2

4. Check inflammatory markers (ESR, CRP)—ESR >70 mm/h combined with ulcer >2 cm² and positive probe-to-bone significantly increases osteomyelitis likelihood. 1, 2

5. If both X-ray and MRI are positive, proceed with bone culture/biopsy during surgical debridement for definitive diagnosis and antibiotic guidance. 1

Critical Pitfalls to Avoid

• Never rely on X-rays alone in this high-risk patient—negative X-rays do not exclude osteomyelitis. 1, 2

• Do not wait 2-3 weeks for repeat X-rays if initial films are negative—this patient needs aggressive evaluation now given his amputation risk. 1

• Unstageable ulcers require debridement before accurate assessment—you cannot properly evaluate depth, probe-to-bone, or wound characteristics through eschar. 1, 6

• Do not order CT as your advanced imaging—it adds little value compared to MRI for this indication. 1

• Remember that MRI can be falsely positive in Charcot neuroarthropathy or post-traumatic changes, so correlation with clinical findings is essential. 1, 4