What causes pain in the sole of the foot in an adult with no significant medical history?

Pain in the Sole of the Foot: Causes and Diagnostic Approach

Plantar fasciitis is the most common cause of sole (plantar) foot pain in adults, presenting characteristically with sharp heel pain during the first steps in the morning or after prolonged sitting. 1, 2

Primary Causes by Location

Plantar Heel Pain (Most Common)

• Plantar fasciitis accounts for the majority of plantar foot pain cases, affecting more than 1 million persons per year in the United States 1
• Pain localizes to the medial plantar calcaneal region with point tenderness at the calcaneal tuberosity 1, 3
• Classic presentation includes severe pain with first weight-bearing steps in the morning that improves with activity 1, 2
• Risk factors include obesity, excessive foot pronation, excessive running, and prolonged standing 1

Central Heel Pain

• Calcaneal stress fracture presents with progressively worsening pain following increased walking activity or change to a harder walking surface 4, 2
• The calcaneal squeeze test (compression from medial to lateral) is highly suspicious for stress fracture 4, 2
• Heel pad syndrome causes deep, bruise-like pain in the middle of the heel, especially in older and obese patients 2, 3

Neurologic Causes

• Nerve entrapment (including tarsal tunnel syndrome) causes plantar heel pain accompanied by burning, tingling, or numbness—distinguishing it from mechanical causes 4, 2
• Pain radiates along the distribution of the posterior tibial nerve through the medial ankle 2, 3

Diagnostic Algorithm

History Red Flags to Elicit

• Timing of pain: Morning pain with first steps suggests plantar fasciitis; progressively worsening pain with activity suggests stress fracture 1, 2
• Quality of pain: Sharp, localized pain indicates mechanical causes; burning/tingling indicates neurologic causes 4, 2
• Activity changes: Recent increase in walking or change to harder surfaces suggests stress fracture 4, 2
• Bilateral symptoms or other joint pain: Consider systemic inflammatory arthropathies 3

Physical Examination Findings

• Palpate the medial calcaneal tuberosity: Point tenderness confirms plantar fasciitis 1, 3
• Perform passive dorsiflexion of ankle and first toe: Reproducing plantar fascia pain confirms the diagnosis 1
• Calcaneal squeeze test: Medial-to-lateral compression causing pain suggests stress fracture 4, 2
• Assess for neurologic symptoms: Test sensation and perform Tinel's sign at the tarsal tunnel 2, 3

Imaging Approach

• Initial imaging: Conventional radiography (weight-bearing foot X-rays) is the first imaging study for chronic foot pain 5
• If radiographs negative but pain persists >1 week: MRI without contrast or CT without contrast are equivalent alternatives 6, 4
• For suspected stress fracture with negative X-rays: Technetium bone scanning is recommended, as symptoms often precede radiographic findings 6, 4
• Important caveat: Initial radiographs have poor sensitivity (12-56%) for stress fractures, so negative X-rays do not exclude the diagnosis 7

Less Common but Important Causes

Traumatic

• Acute calcaneal fracture from fall onto heel from height causes diffuse rearfoot pain requiring history of trauma and radiographic confirmation 6, 4

Infectious/Inflammatory

• Osteomyelitis or soft tissue infections rarely cause heel pain but require proper diagnostic testing and consultation when suspected 6, 4
• Consider in patients with diabetes, immunocompromise, or overlying skin breakdown 5

Neoplastic

• Tumors (malignant or benign) are rare but require referral if pain is constant at rest or progressively worsening without mechanical explanation 6, 4

Critical Pitfalls to Avoid

• Do not dismiss stress fractures based on negative initial radiographs alone—symptoms precede radiographic changes by weeks 6, 4, 7
• Reexamine patients 3-5 days post-injury if initial examination is limited by excessive swelling 6
• Recognize neurologic causes early: Burning, tingling, or numbness requires subspecialist referral for electromyography and nerve conduction studies 6, 4
• Avoid corticosteroid injections near the Achilles tendon due to rupture risk, though they may be used judiciously for plantar fasciitis 6

When Conservative Treatment Fails

• No improvement after 6-8 weeks of appropriate conservative treatment warrants referral 6
• 90% of plantar fasciitis cases resolve with conservative measures (rest, stretching, NSAIDs, orthotics, heel cushions) but may take 3-6 months 1, 8
• Chronic recalcitrant cases lasting ≥6 months may consider extracorporeal shock wave therapy or surgical intervention 1, 8