Diagnosing Plantar Fasciitis
Plantar fasciitis is predominantly a clinical diagnosis based on characteristic history and physical examination findings, with imaging reserved for cases that persist beyond 3 months or when the diagnosis is uncertain. 1, 2
Clinical Diagnosis
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 3, 4
- Pain that worsens at the end of the day after prolonged standing or walking 4
- History of risk factors including obesity, excessive foot pronation, excessive running, prolonged standing, or limited ankle dorsiflexion 3, 4
Physical Examination Findings
- Point tenderness to palpation at the medial plantar calcaneal region, specifically at the origin of the plantar fascia on the medial tubercle of the calcaneus 3, 5
- Discomfort elicited by passive ankle and first toe dorsiflexion, which stretches the plantar fascia 3
- Physical examination findings are often limited to this focal tenderness, making it a highly specific diagnostic feature 4
When to Order Imaging
Initial Imaging Approach
If the diagnosis is unclear or symptoms persist beyond 3 months despite treatment, obtain weightbearing radiographs as the initial imaging study 1, 2. The American College of Radiology recommends this approach, as 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, 2.
Advanced Imaging for Recalcitrant Cases
MRI is the most sensitive imaging study for definitive diagnosis when the diagnosis remains uncertain after initial evaluation 1, 2. MRI allows accurate characterization of the plantar fascia and adjacent soft tissues/bones, and should be considered for recalcitrant cases that don't respond to initial treatment 1, 3.
Ultrasound is a reasonable and inexpensive alternative diagnostic tool for patients with pain persisting beyond 3 months 4. Ultrasound demonstrates good diagnostic accuracy with 80% sensitivity and 88% specificity compared to MRI 1, 2. Key ultrasound findings supporting the diagnosis include:
- Increased plantar fascia thickness (>4mm is abnormal) 1
- Abnormal focal echogenicity within the plantar fascia 2
- Perifascial edema 1, 2
- Edema around the plantar fascia 2
US elastography shows even higher diagnostic accuracy with 95% sensitivity and 100% specificity compared to conventional ultrasound (66% sensitivity and 75% specificity) 2.
Differential Diagnosis to Exclude
When evaluating heel pain, consider these alternative diagnoses that can present similarly:
- Calcaneal stress fracture - can present with similar symptoms and should be excluded with imaging 1
- Tarsal tunnel syndrome - neurologic heel pain from nerve entrapment that may require electromyography or nerve conduction studies 6
- Plantar fascia rupture - a potential complication that can be diagnosed with MRI or ultrasound 1
- Calcaneal apophysitis - the most common cause of heel pain in adolescents 6
Critical Pitfall
MRI findings must always be correlated with clinical symptoms to avoid overcalling plantar fasciitis, as some imaging findings can be seen in asymptomatic patients 2. This is why the clinical diagnosis remains paramount, and imaging should not replace a thorough history and physical examination but rather supplement it when needed.