What is the pathophysiology of plantar fasciitis?

Pathophysiology of Plantar Fasciitis

Plantar fasciitis is primarily a chronic degenerative process rather than an inflammatory condition, characterized by fibroblastic hypertrophy and collagen degeneration at the plantar fascia origin on the calcaneus. 1, 2

Degenerative vs. Inflammatory Mechanisms

The pathophysiology involves two distinct but potentially overlapping processes:

• Degenerative pathway (predominant): Histologic examination reveals chronic degenerative changes with localized fibrosis, granulomatous changes, and collagen breakdown rather than acute inflammation 2, 3
• Inflammatory pathway (secondary): When present, involves vasodilation and immune system activation, though this is less common than traditionally believed 1
• The term "fasciitis" is actually a misnomer since true inflammation is not the primary pathologic finding in most cases 2

Biomechanical Stress and Repetitive Microtrauma

The fundamental mechanism involves repetitive mechanical overload:

• Excessive tensile forces at the plantar fascia origin create repetitive microtrauma during weight-bearing activities 1, 4
• Increased plantar pressures during walking and standing, particularly in the midfoot and heel regions, contribute to cumulative tissue damage 5
• The plantar fascia experiences peak stress during the terminal stance phase of gait when the heel lifts and the fascia must support body weight 4

Anatomical and Biomechanical Risk Factors

Several structural abnormalities increase mechanical stress on the plantar fascia:

• Pes planus (flat foot) results in increased plantar pressures and altered load distribution, creating repetitive biomechanical stress 5, 1
• Pes cavus (high arch) similarly disrupts normal pressure distribution 4
• Tight Achilles tendon is found in approximately 80% of patients with plantar fasciitis, creating increased tension transmitted through the posterior chain to the plantar fascia 6
• Gastrocnemius-soleus tightness correlates positively with heel pain severity, as the triceps surae-Achilles tendon-plantar aponeurosis complex functions as an integrated biomechanical unit 6

Fascial System Alterations

Recent understanding emphasizes the role of the fascial continuum:

• Structural changes in the muscle-tendon-fascia complex due to overuse or injury alter mechanical properties throughout the posterior chain 6
• Reduced ankle dorsiflexion increases compensatory stress on the plantar fascia during gait 2
• The fasciae of the soleus and their connections to the Achilles tendon create a mechanical pathway for transmitting abnormal forces to the plantar aponeurosis 6

Systemic and Metabolic Factors

Beyond mechanical causes, systemic conditions contribute:

• Obesity increases absolute load on the plantar fascia during weight-bearing 1, 4
• Diabetes mellitus is associated with plantar fasciitis, likely through multiple mechanisms including altered tissue healing and biomechanical changes 1
• Rheumatologic diseases are linked to plantar fasciitis development 2
• Genetic factors may predispose certain individuals to fascial degeneration 2

Common Pitfalls in Understanding

The traditional inflammatory model has led to treatment approaches that may not address the underlying degenerative pathology. Recognizing that this is primarily a degenerative condition with fibroblastic changes rather than acute inflammation helps explain why anti-inflammatory treatments often provide limited long-term benefit 2, 3. The natural history remains poorly established, making it difficult to distinguish spontaneous resolution from treatment effects 4.