What is the diagnostic approach for Morton's neuroma?

Diagnostic Approach for Morton's Neuroma

Begin with plain radiographs to exclude other causes of webspace pain, then proceed directly to ultrasound or MRI for confirmation, with ultrasound being preferred for its ability to perform dynamic examination and immediate clinical correlation during the physical exam. 1, 2, 3

Initial Imaging: Radiographs First

• Obtain plain radiographs as the first imaging study, even though they are insensitive for diagnosing Morton's neuroma itself 2, 3
• Radiographs serve to exclude alternative diagnoses including osteoarthritis, Freiberg's infraction, and stress fractures that can mimic Morton's neuroma symptoms 2, 3
• After negative or equivocal radiographs, proceed immediately to advanced imaging 2

Advanced Imaging: Ultrasound vs MRI

The American College of Radiology recommends both ultrasound and MRI as preferred imaging modalities, with comparable high diagnostic accuracy 1, 2, 3:

Ultrasound (Preferred in Most Cases)

• Sensitivity of 90% for detecting Morton's neuroma 1, 3
• Primary advantage: allows dynamic examination with real-time clinical correlation during physical testing 1, 3, 4
• Enables performance of clinical maneuvers (thumb-index finger squeeze, Mulder's click, foot squeeze tests) under direct visualization 4, 5
• Can guide therapeutic interventions immediately if diagnosis is confirmed 4, 5
• Important caveat: subject to interoperator variability based on technique and examiner experience 5

MRI (Alternative or Complementary)

• Sensitivity of 93% for detecting Morton's neuroma 1, 2, 3
• Superior for differential diagnosis when multiple pathologies are suspected 3, 6
• More conspicuous when patient is positioned prone with foot in plantar flexion rather than supine 6
• Better for identifying alternative diagnoses including intermetatarsal bursitis, stress fractures, stress reactions, synovial cysts, and soft tissue masses 6
• Use MRI without contrast for persistent pain after negative radiographs 1

Clinical Examination Details

While imaging confirms the diagnosis, specific clinical findings to assess include 4, 7:

• Pain location: typically in the third intermetatarsal space (between 3rd and 4th digits), less commonly the second space 4, 7
• Symptom pattern: dull or sharp pain, numbness/tingling in the 3rd and 4th digits, burning sensation, cramping, or sensation of "walking on a stone" around metatarsal heads 4
• Physical examination maneuvers: thumb-index finger squeeze test, Mulder's click (palpable click with compression), and foot squeeze test 4, 5

Diagnostic Algorithm Summary

1. Obtain plain radiographs first to exclude bony pathology 2, 3
2. Proceed to ultrasound as first-line advanced imaging for dynamic assessment and immediate clinical correlation 1, 3
3. Consider MRI if ultrasound is equivocal, operator expertise is limited, or multiple differential diagnoses need evaluation 3, 6
4. Use imaging to confirm exact localization and number of neuromas before treatment planning 4

Common Pitfalls to Avoid

• Do not rely on clinical examination alone without imaging confirmation, as multiple forefoot pathologies present similarly 1, 6
• Do not skip radiographs despite their insensitivity for Morton's neuroma—they are essential for excluding other causes 2, 3
• Ensure proper patient positioning for MRI (prone with plantar flexion) to maximize neuroma conspicuity 6
• Recognize that Morton's neuroma is not a true neuroma but rather perineural fibrosis, which affects treatment expectations 7, 5