How should I evaluate and treat chronic left foot pain near the great toe in a patient who was injured by a rubber bullet years ago?

Chronic Foot Pain from Remote Penetrating Trauma: Evaluation and Management

Start with plain radiographs of the foot in three standard projections (AP, lateral, and 45° oblique) to identify retained foreign body, fracture sequelae, or post-traumatic arthritis, then proceed to MRI without contrast if radiographs are negative or equivocal. 1

Initial Imaging Approach

Radiography is mandatory as the first-line study because:

• Rubber bullets are radiopaque and radiographic evaluation has approximately 98% sensitivity for detecting metallic foreign bodies 1
• Standard radiographs identify fracture malunion, post-traumatic arthritis, or osseous deformity from the original injury 1
• Weight-bearing views should be obtained when feasible to assess joint alignment and functional biomechanics 1, 2
• The penetrating trauma history makes this an explicit exception to clinical decision rules like Ottawa criteria 1

When Radiographs Are Negative or Non-Diagnostic

MRI foot without IV contrast is the next appropriate study because:

• MRI detects occult fractures, bone marrow edema, stress reactions, tendon pathology, ligament injuries, and nerve compression syndromes invisible on radiographs 1, 2
• MRI visualizes chronic soft tissue sequelae including tendon tears, scar tissue, and nerve entrapment that may explain persistent pain years after injury 1, 2
• Contrast administration is not routinely necessary for evaluating chronic post-traumatic pain 1

Ultrasound as a Complementary Tool

Consider ultrasound for specific clinical scenarios:

• Dynamic examination allows assessment of tendon stability and identification of tears with direct clinical correlation 1, 2
• Power Doppler identifies increased vascularity in chronic inflammatory conditions like sesamoiditis or intermetatarsal bursitis 1, 2
• Ultrasound has 90% sensitivity for non-radiopaque foreign bodies (though rubber bullets are typically radiopaque) 1

Critical Pitfalls to Avoid

Do not skip initial radiographs even if the injury occurred years ago:

• Retained foreign material may cause chronic inflammation or serve as a nidus for infection 1
• Post-traumatic arthritis develops insidiously and requires baseline imaging 1
• Stress fractures from altered biomechanics have only 12-56% sensitivity on initial radiographs but may be visible on chronic follow-up films 2

Do not order ankle radiographs when evaluating forefoot pain:

• Standard foot radiographs are required for proper visualization of the great toe region 2, 3
• Three projections (AP, lateral, oblique) are essential for complete assessment 1

Differential Diagnosis to Consider

Based on the location near the great toe, evaluate for:

• Sesamoiditis: Plantar great toe pain with increased blood supply on Power Doppler ultrasound 2
• Chronic plantar plate injury: Detectable on MRI or Power Doppler ultrasound 1, 2
• Post-traumatic arthritis of the first metatarsophalangeal joint: Visible on radiographs 1
• Nerve entrapment from scar tissue: Best visualized on MRI 1, 2
• Retained foreign body with chronic inflammatory response: Radiographs or ultrasound 1

When to Consider CT

CT is not routinely the next study after radiographs for this clinical scenario, but consider it if:

• Surgical planning is needed for complex osseous deformity 1
• Precise localization of a retained foreign body is required before extraction 1
• MRI is contraindicated 1

Clinical Examination Priorities

Focus your physical examination on:

• Point tenderness over the sesamoids versus the metatarsophalangeal joint versus the metatarsal shaft 2
• Pain with passive dorsiflexion or plantarflexion of the great toe (suggests joint pathology) 2
• Palpable mass or foreign body 1
• Neurologic deficits suggesting nerve injury or entrapment 1, 4
• Comparison with the contralateral foot for subtle deformities 1, 2