What is the cause and treatment of burning pain in the foot when flexing?

Burning Pain in Foot When Flexing: Diagnosis and Treatment

Most Likely Diagnosis

The burning pain in your foot with flexion most likely represents peripheral neuropathy (small fiber sensory neuropathy) or nerve entrapment, particularly if the pain has a burning quality and occurs with specific movements. 1

Key Diagnostic Features to Identify

Pain Characteristics That Point to Specific Diagnoses

• Burning pain with numbness or tingling strongly suggests neurologic causes including small fiber sensory polyneuropathy (SFSN), which manifests as burning pain affecting the feet, often with allodynia 1
• Pain location matters critically: Posterior heel pain indicates Achilles tendonitis or bursitis; lateral heel pain suggests Haglund's deformity or sinus tarsi syndrome; diffuse heel pain indicates stress fracture 2
• Pain with dorsiflexion (flexing foot upward) plus lateral pain suggests calcaneofibular ligament sprain or lateral ankle ligament injury 2
• Burning pain radiating to toes (especially 3rd and 4th) indicates Morton neuroma with interdigital neuronal thickening 3

Critical Examination Findings

• Point tenderness location: Palpate the Achilles insertion, lateral malleolus, posterior superior calcaneus, lateral calcaneal wall, and calcaneofibular ligament course to differentiate diagnoses 2
• Calcaneal compression test (squeezing calcaneus medial to lateral) suggests stress fracture if positive 2
• Assess for sensory loss using 10-g monofilament testing or Ipswich touch test plus one additional test (pinprick, temperature, or vibration) to identify peripheral neuropathy 1
• Check for autonomic signs: Abnormalities of sweating and circulatory instability in the feet indicate diabetic distal symmetric polyneuropathy with autonomic involvement 1

Initial Imaging Approach

Start with plain radiographs of the foot as the first imaging study for chronic foot pain of unknown etiology. 1

• Radiography is usually appropriate initially with sensitivities of 80-100% and specificities of 97-98% for many foot pathologies 1
• MRI, CT, and bone scans are NOT recommended as first-line imaging for chronic foot pain of unknown etiology 1
• If radiographs are negative but pain persists >1 week, MRI without contrast or CT without contrast are equivalent alternatives 2
• For suspected stress fracture with negative radiographs, technetium bone scanning is recommended as symptoms often precede radiographic visibility 2

Treatment Algorithm Based on Diagnosis

For Neuropathic Burning Pain (Most Likely Given Your Symptoms)

• Immediate subspecialist referral for neurologic evaluation including electromyography, nerve conduction studies, and MRI 2
• Assess for diabetes, vitamin deficiencies, and systemic causes as peripheral neuropathy is present in 78% of diabetic foot ulcerations 1
• Perform comprehensive foot examination including inspection, assessment of deformities, neurological assessment, and vascular assessment 1

For Plantar Fasciitis (If Pain is Plantar and Worse with First Steps)

• First-line treatment: Regular calf-muscle and plantar fascia stretching exercises (3-5 times daily), over-the-counter heel cushions and arch supports, activity limitation, proper footwear 4
• NSAIDs for pain relief and inflammation 4
• If no improvement after 6 weeks: Add padding/strapping, weight management, customized orthotic devices 4
• If no improvement after 2-3 months: Consider cast immobilization, extracorporeal shock wave therapy, or surgical evaluation 4, 3

For Achilles Tendinopathy (If Pain is Posterior, 2-6 cm Above Heel)

• Primary treatment: Eccentric strengthening exercises 3
• Additional measures: Open-backed shoes, heel lifts, NSAIDs, decreased activity, stretching exercises 2
• Extracorporeal shockwave therapy if conservative measures fail 3
• AVOID corticosteroid injections near the Achilles tendon due to rupture risk 2, 4

For Morton Neuroma (If Burning Radiates to Toes)

• First-line therapy: Reduce pain-causing activities, orthotics, interdigital corticosteroid injection 3
• Note: Approximately 30% may not respond to conservative treatment and require surgical evaluation 3

Critical Pitfalls to Avoid

• Never inject corticosteroids near the Achilles tendon as this significantly increases rupture risk 2, 4
• Always reexamine 3-5 days post-injury as excessive swelling and pain can limit initial examination within 48 hours 2
• Do not overlook stress fractures as patients often report increased walking activity before symptom onset and radiographs may initially be negative 2
• Recognize that burning feet may be the only manifestation of hereditary sensory neuropathy with minimal clinical or neurophysiologic findings 5

When to Refer

Refer immediately if:

• Burning or tingling suggests neurologic causes requiring subspecialist evaluation 2
• No improvement after 6-8 weeks of appropriate conservative treatment 2, 4
• Need for advanced diagnostic testing (EMG, nerve conduction studies) 2

Annual comprehensive foot examinations are mandatory for anyone with diabetes or prior neuropathy to prevent ulceration and amputation 1