**1. Incidence and etiology of plantar fasciitis**

About 7% of the population >65 years suffer from a painful heel, even though younger people are often affected, too [1]. The most common cause of this symptom is the so‐called "plantar fasciitis" [2]. This term is widely used, although "plantar fasciopathy" or "plantar fasciosis" would be a better description to point out the degenerative nature of the disease. However, as

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more than 1100 citations in Pubmed quote "plantar fasciitis" (in comparison with only 50), we will use the traditional term in the following.

Plantar fasciitis has been associated with obesity, with acute or chronic work overload, or with work on hard surfaces [2, 3]. It seems that physiological degeneration of the fascia at the calca‐ neal insertion exacerbates due to repetitive microtraumas caused by vertical compression [4]. This causes inflammatory tissue reactions. As a result, the fascia is thickened with an associated fluid collection to 4.0 mm and more in ultrasonography [5]. Furthermore, this inflammation may trigger bone formation, the so‐called "plantar heel spur." This process has been studied intensively by Kumai and Benjamin [6]. They proposed three stages of spur growth: "(a) an ini‐ tial formation of cartilage cell clusters and fissures at the plantar fascia enthesis; (b) thickening of the subchondral bone plate at the enthesis as small spurs form; and (c) development of verti‐ cally oriented trabeculae buttressing the proximal end of larger spurs" [6]. The first description of this spur formation and correlation with the clinical symptoms was carried out by Plettner in 1900 [7]. However, not every heel spur is associated with heel pain, as these spurs are found in 11–16% of the normal asymptomatic population [4]. On the other hand, some patients with painful plantar fasciitis do not have a radiographic confirmation of a spur formation.

A similar mechanism (although caused by longitudinal traction and not by vertical compression) of bone formation has been described at the insertion of the Achilles tendon [8].

According to the American clinical practice guidelines from 2010, diagnosis is established by the typical anamnesis and the characteristic localizations of tenderness. Still, weight‐bearing radiographs are also recommended [9].
