What is the appropriate diagnostic workup for suspected plantar fasciitis?

Diagnostic Workup for Plantar Fasciitis

Plantar fasciitis is predominantly a clinical diagnosis that does not require imaging in most cases; reserve imaging for symptoms persisting beyond 3 months or when the diagnosis is uncertain. 1, 2

Clinical Diagnosis

The diagnosis is established through history and physical examination findings alone in the majority of patients. 2, 3, 4

Key Historical Features

• Stabbing, nonradiating pain on the proximal medioplantar surface of the foot, worst with first steps in the morning or after prolonged sitting 2, 3, 4
• Pain that worsens at the end of the day after prolonged standing 4
• Risk factors include obesity, excessive foot pronation, excessive running, prolonged standing, and limited ankle dorsiflexion 2, 3, 4

Physical Examination Findings

• Point tenderness at the medial plantar calcaneal region where the plantar fascia originates on the medial tubercle of the calcaneus 2, 3, 4
• Discomfort elicited by passive ankle and first toe dorsiflexion 2
• Assessment for gastrocnemius tightness, which is commonly associated 3

Imaging Studies (When Indicated)

If the diagnosis is unclear or symptoms persist beyond 3 months despite conservative treatment, obtain weightbearing radiographs as the initial imaging study. 1, 5, 6

Imaging Algorithm

First-line imaging: Weightbearing radiographs have 85% sensitivity and 95% specificity for evaluating thickened plantar fascia and fat pad abnormalities, and help exclude other pathologies such as calcaneal stress fractures 1, 5, 6

Second-line imaging when diagnosis remains uncertain:

• MRI is the most sensitive imaging study for definitive diagnosis, allowing accurate characterization of the plantar fascia and adjacent soft tissues and bones 7, 1, 5, 6
• MRI findings include increased plantar fascia thickness and abnormal tissue signal 2

Alternative imaging option:

• Ultrasound demonstrates 80% sensitivity and 88% specificity compared to MRI and is a reasonable, inexpensive diagnostic tool 7, 1, 4
• Key ultrasound findings: plantar fascia thickness >4mm (abnormal), abnormal focal echogenicity, perifascial edema, and edema around the plantar fascia 1, 6
• US elastography shows even higher diagnostic accuracy with 95% sensitivity and 100% specificity compared to conventional ultrasound 1, 5, 6

Critical Imaging Pitfall

Always correlate MRI findings with clinical symptoms to avoid overcalling plantar fasciitis, as some imaging findings can be present in asymptomatic patients 7, 1, 6

Differential Diagnoses to Exclude

• Calcaneal stress fracture presents with similar symptoms and should be excluded with imaging 1, 5
• Tarsal tunnel syndrome causes neurologic heel pain from nerve entrapment and may require electromyography or nerve conduction studies 1
• Plantar fascia rupture is a potential complication diagnosed with MRI or ultrasound 1, 5
• Calcaneal apophysitis is the most common cause of heel pain in adolescents 1

When Advanced Imaging May Be Considered

Bone scan with SPECT or SPECT/CT can differentiate plantar fasciitis from calcaneal stress or avulsion fractures through characteristic patterns of abnormal uptake on 3-phase bone scintigraphy, though MRI and ultrasound remain the most frequently used modalities 7, 6

Laboratory Testing

Laboratory tests are not routinely indicated but may be useful for differential diagnoses when rheumatologic diseases are suspected 8