What causes pain and swelling on the dorsal aspect of the foot without a clear injury?

Pain and Swelling on Top of Foot Without Injury

In a patient with diabetes and neuropathy presenting with a red, warm, swollen foot without clear trauma, active Charcot neuro-osteoarthropathy (CNO) must be suspected immediately and treated with prompt immobilization, as delayed diagnosis leads to devastating consequences including fractures, deformity, ulceration, and amputation. 1

Primary Diagnostic Considerations

Charcot Neuro-Osteoarthropathy (Most Critical in Diabetics)

• Active CNO should always be suspected when a person with diabetes and neuropathy presents with a unilateral red, warm, swollen foot with intact skin and no history of ulceration. 1
• Clinical signs include hyperaemia, increased foot skin temperature, and edema, with pain that may be absent or relatively mild due to sensory neuropathy. 1
• Temperature difference ≥2°C between the affected and unaffected foot at the same anatomical location strongly suggests active CNO. 1
• Left untreated, CNO presents high risk of bone fractures, dislocations, deformity, ulceration, infection, and amputation with major lifelong consequences. 1

Diabetic Foot Infection (Must Be Excluded)

• Infection requires at least two of the following: local swelling/induration, erythema >0.5 cm around any wound, local tenderness/pain, local warmth, or purulent discharge. 1
• Other inflammatory conditions must be excluded: trauma, gout, acute Charcot neuro-osteoarthropathy, fracture, thrombosis, and venous stasis. 1
• The presence of ulceration and infection does not preclude underlying active Charcot—both can coexist. 1

Stress Fracture

• Presents with progressively worsening pain following increased walking activity or change to harder walking surface. 2, 3
• Calcaneal squeeze test (medial-to-lateral compression) is highly suspicious for calcaneal stress fracture. 2, 3
• Symptoms often precede radiographic findings, requiring technetium bone scanning or MRI for early diagnosis. 2, 3

Other Differential Diagnoses

• Gout: Consider in patients with acute onset, severe pain, and history of hyperuricemia or prior attacks. 1
• Deep venous thrombosis: Must be excluded with appropriate clinical assessment and D-dimer/ultrasound if indicated. 1
• Soft tissue infection without diabetes: Requires at least two inflammatory signs (redness, warmth, swelling, tenderness, purulent discharge). 1

Immediate Management Algorithm

Step 1: Assess for Diabetes and Neuropathy

• If diabetes with neuropathy is present, initiate knee-high immobilization/offloading promptly while further diagnostic studies are performed to confirm or rule out active CNO. 1
• This is a strong recommendation even before imaging confirmation due to the catastrophic consequences of delayed treatment. 1

Step 2: Clinical Examination

• Palpate for point tenderness: Achilles insertion, lateral malleolus, posterior superior calcaneus, lateral calcaneal wall, and calcaneofibular ligament course. 2
• Perform calcaneal compression test (medial-to-lateral squeeze) to evaluate for stress fracture. 2, 3
• Measure skin temperature using infrared thermometry at multiple sites on both feet, comparing the highest temperature on affected foot to the same anatomic point contralaterally. 1
• Assess for signs of infection: erythema, warmth, purulent discharge, or open wounds. 1

Step 3: Initial Imaging

• Obtain plain X-rays of the foot in all cases to evaluate for fractures, dislocations, or bone destruction. 1
• Plain radiographs may be normal in early CNO (stage 0) and early stress fractures. 1, 2

Step 4: Advanced Imaging (If Diagnosis Unclear)

• MRI is the preferred advanced imaging modality for diagnosing active CNO, showing bone marrow edema without fractures in early stages. 1
• MRI can be difficult to differentiate CNO from osteomyelitis, as both show bone marrow edema—expert radiologist opinion is essential. 1
• If MRI unavailable or contraindicated, consider white blood cell-labeled radionuclide scan, SPECT/CT, or FDG-PET. 1
• Technetium bone scanning for suspected stress fracture with negative initial radiographs. 2, 3

Step 5: Laboratory Testing

• Markedly elevated erythrocyte sedimentation rate suggests osteomyelitis in suspected cases. 1
• Consider inflammatory markers (CRP, WBC) if infection is suspected. 1

Critical Pitfalls to Avoid

• Never delay immobilization in diabetic patients with neuropathy and a hot swollen foot while waiting for imaging—the consequences of untreated CNO are devastating. 1
• Do not assume the absence of pain rules out serious pathology in diabetic patients with neuropathy, as pain may be minimal or absent. 1
• Do not diagnose based on imaging alone—combine symptoms, clinical signs, and imaging findings. 1
• Reexamine 3-5 days post-presentation if initial examination is limited by excessive swelling and pain. 2
• Be aware that stress fractures may have negative initial radiographs—maintain clinical suspicion and consider bone scan or MRI if symptoms persist. 2, 3

When to Refer

• Immediate subspecialist referral for suspected active CNO to prevent progression to deformity and ulceration. 1
• Suspected osteomyelitis requiring bone biopsy for definitive diagnosis or antibiotic sensitivity testing. 1
• No improvement after 6-8 weeks of appropriate conservative treatment for other conditions. 2
• Consideration of surgical intervention for recalcitrant cases. 2