Plantar fasciitis is the most commonly reported cause of chronic pain beneath the heel [1, 2]. The condition is characterised by pain at the calcaneal origin of the plantar fascia, made worse by weight-bearing after prolonged periods of rest . The epidemiology of plantar fasciitis in the general population is currently uncertain. An Australian population-based study involving 3,206 randomly selected participants has reported a heel pain prevalence of 3.6% . A North American study of adults aged over 65 years found that 7% had tenderness beneath the heel . It has also been estimated that 1 million physician visits per year in the United States are for the diagnosis and treatment of plantar fasciitis . In addition, the disorder is estimated to account for approximately 8% of all running-related injuries [6, 7].
The underlying pathology of plantar fasciitis is poorly understood, though the majority of histological studies report a predominance of degenerative changes at the plantar fascia enthesis. The most common pathological features are deterioration of collagen fibres, increased secretion of ground substance proteins, focal areas of fibroblast proliferation and increased vascularity [8–11]. The presence of biochemical markers of inflammation (e.g. cytokines and prostaglandins) have not been well investigated, however, several studies report non-specific evidence of local inflammatory change [11–13]. As described in relation to tendinopathy , it is feasible that plantar fasciitis is a disorder that proceeds through a spectrum of underlying processes. However, evidence for histological change over time is currently lacking, as current studies have only examined specimens obtained from patients undergoing surgery for long-standing symptoms. Therefore, the underlying pathology occurring early in the development of plantar fasciitis is currently unknown.
Plantar fasciitis is commonly described in the literature as a self-limiting condition [1, 2]. This view is supported by the findings of a systematic review, in which plantar heel pain was found to resolve over time regardless of treatment type (including placebo) . Nonetheless, plantar fasciitis can be a very painful and disabling condition prior to resolution of symptoms, causing a negative impact on health-related quality of life .
Many interventions are used for the management of plantar fasciitis  and corticosteroid injection is a common choice among clinicians. Surveys of American podiatrists  and orthopaedic surgeons  have reported that approximately 75% of respondents used and/or recommended this intervention. In addition, a systematic review found that corticosteroid injection is the second most frequently described treatment for plantar fasciitis in the medical literature .
Despite the widespread use of corticosteroid injection for plantar fasciitis, only two randomised controlled trials have tested the effect of this treatment in comparison to placebo injection [21, 22]. By using placebo solution as a comparator, these trials were able to control for potential treatment benefits not due to the pharmacological action of corticosteroids. One trial compared the effect of 25 mg prednisolone mixed with lignocaine versus lignocaine alone (placebo), and found a significant difference in pain reduction favouring corticosteroid one month after treatment . No significant differences between groups were detected in this trial at either three or six months after treatment. However, a large proportion of participants were lost to follow-up, so the authors were unable to make conclusions regarding corticosteroid efficacy in the longer term. An earlier trial compared the effect of 25 mg hydrocortisone versus normal saline (placebo), and found no significant difference in pain reduction between groups two months after treatment . However, this trial had a very small sample size (19 participants) and was therefore statistically underpowered to detect clinically worthwhile differences.
The use of ultrasound in clinical practice has become increasingly popular due to decreased equipment costs, and the ability to perform invasive procedures with better targeting of anatomical structures . Other advantages include the production of high resolution images without exposure to ionizing radiation, and the ability to assess tissues with real-time dynamics . Furthermore, in the treatment of plantar fasciitis, corticosteroid injection performed with ultrasound guidance has been shown to produce longer lasting pain relief than injection guided by palpation .
The findings of existing clinical trials provide some support for the use of corticosteroid injection in the short-term management of plantar fasciitis [1, 15]. However, a recent systematic review concluded that the effectiveness of this treatment has not been sufficiently established , indicating that further research is required. Therefore, the aim of this trial is to investigate the effectiveness of ultrasound-guided corticosteroid injection for treatment of plantar fasciitis over a 12 week period.