Can Pes Planus Cause Plantar Fasciitis?
Yes, pes planus (flat feet) is a recognized risk factor and contributing cause of plantar fasciitis, though the exact biomechanical relationship remains incompletely understood.
The Evidence for the Association
The link between flat feet and plantar fasciitis is supported by multiple lines of evidence, though with some nuance:
Direct Clinical Evidence
A prospective study of 82 patients with plantar heel pain found that the mean calcaneal pitch (a measure of arch height) was 15.99 degrees compared to 20.54 degrees in normal subjects—a statistically significant difference 1. This demonstrates that patients with plantar fasciitis have measurably flatter feet than those without heel pain.
In clinical practice, pes planus was identified as a distinct cause of plantar heel pain in 4.8% of cases, while appearing as a contributing biomechanical factor in many more 2. Recent reviews consistently list pes planus among the common anatomical deformities that lead to plantar fasciitis 3, 4.
The Proposed Mechanism
The traditional theory holds that flat foot architecture creates excessive tensile strain within the plantar fascia as the medial longitudinal arch collapses during weight-bearing 5. This repetitive strain produces microscopic tears at the fascial origin on the medial calcaneal tuberosity.
Important Caveats
However, the relationship is more complex than simple cause-and-effect:
Scientific support for arch mechanics as the sole causative factor is equivocal 5. While clinical doctrine strongly supports this link, the biomechanical evidence is not as robust as the anecdotal clinical experience suggests.
Histological studies of chronic plantar fasciitis rarely show inflammation, instead revealing degenerative changes 5. This suggests the pathophysiology may involve stress-shielding, vascular disturbances, or metabolic factors beyond pure mechanical overload.
Not all patients with flat feet develop plantar fasciitis, and not all plantar fasciitis patients have flat feet, indicating multiple contributing factors including obesity, prolonged standing, inappropriate footwear, and biomechanical issues like excessive subtalar pronation 3, 4.
Clinical Implications for Your Patient
For an adult presenting with morning heel pain and flat feet:
Pes planus should be considered a significant contributing factor to their plantar fasciitis, particularly if they have other risk factors (obesity, prolonged standing, recent increase in activity).
Treatment should address the arch mechanics. The American College of Foot and Ankle Surgeons guidelines specifically recommend arch supports as part of initial management 6. Start with over-the-counter arch supports initially, progressing to custom orthotics if symptoms don't improve after 6 weeks 6.
Avoid flat shoes and barefoot walking, as these exacerbate the mechanical stress on already compromised arch structures 6.
The flat foot architecture makes this patient more likely to benefit from orthotic intervention compared to patients with normal arch height.
Bottom Line
While the exact biomechanical pathway remains debated in the literature, clinical evidence clearly demonstrates that pes planus increases risk for plantar fasciitis and should be addressed as part of comprehensive treatment. The relationship is strong enough that addressing arch mechanics through supportive footwear and orthotics forms a cornerstone of evidence-based management 6, 1.