Dose-Related Effect of Extracorporeal Shock Wave Therapy for Plantar Fasciitis
The plantar fascia originates on the inferior side of the calcaneus and is attached to the plantar plate of the metatarsophalangeal joint and the base of the proximal phalanx of the toe. It is important in maintaining the medial longitudinal arch and in absorbing shocks, and is also involved in the windlass mechanism during walking [1,2]. When excessive loads are repeatedly applied to the plantar fascia, acute or chronic inflammatory changes occur in the calcaneus insertion, leading to the development of plantar fasciitis [1,3-6]. Plantar fasciitis is the most common cause of heel pain. Cole et al.  reported that plantar fasciitis is a common condition that occurs in about 10% of the American population.
Generally, pain is aggravated when a patient with plantar fasciitis takes their first steps in the morning but gradually improves with activity. Another characteristic of the condition is the experience of tenderness when pressure is applied to the medial calcaneus on which the plantar fascia originates. Also, when the toes are dorsiflexed, the plantar fascia contracts, and pain increases [3,8,9]. While the precise cause of plantar fasciitis is unknown, it is associated with obesity, middle age, flat foot, and pes cavus .
Treatment methods for plantar fasciitis are diverse, including medication, physical therapy such as stretching exercises, non-surgical treatments such as insole, night splint, and local steroid injection, and surgical treatments such as plantar fascia release. However, the results of the treatment were not consistent [7,10].
Recently, many researchers have demonstrated the effects of extracorporeal shock wave therapy (ESWT) on chronic plantar fasciitis that has previously been resistant to conservative treatment. Their studies have shown that ultrasonography not only alleviates subjective pain but also changes the thickness of the plantar fascia [11-15]. While a number of papers have reported the mechanism and effects of ESWT on plantar fasciitis, no treatment protocol for ESWT has been established. Particularly, much controversy exists regarding the proper amount of energy to be applied to the affected tissue.
Our aim in this study was therefore to investigate the dose-related effect of shock wave therapy at different total energy influx by adjusting the times of sessions and energy flux density (EFD) in patients with chronic plantar fasciitis.
In conclusion, we aimed to evaluate the dose-related effect of ESWT by adjusting the times of sessions and EFD. In applying ESWT to the plantar fasciitis, the adoption of medium-energy level (0.16 mJ/mm2) was more efficient in terms of relieving pain and restoring functional activity than low-energy level (0.08 mJ/mm2) in the same session and showed no adverse effect. However, when different times of sessions were applied for the same total energy influx, different therapeutic effects in the different EFD groups no longer occurred. Therapeutic effect might disclose a dose-related relationship; therefore, EFD and times of sessions are considerable factors when treating with ESWT.