- Open Access
- Open Peer Review
Understanding the nature and mechanism of foot pain
© Hawke and Burns; licensee BioMed Central Ltd. 2009
- Received: 07 May 2008
- Accepted: 14 January 2009
- Published: 14 January 2009
Approximately one-quarter of the population are affected by foot pain at any given time. It is often disabling and can impair mood, behaviour, self-care ability and overall quality of life. Currently, the nature and mechanism underlying many types of foot pain is not clearly understood. Here we comprehensively review the literature on foot pain, with specific reference to its definition, prevalence, aetiology and predictors, classification, measurement and impact. We also discuss the complexities of foot pain as a sensory, emotional and psychosocial experience in the context of clinical practice, therapeutic trials and the placebo effect. A deeper understanding of foot pain is needed to identify causal pathways, classify diagnoses, quantify severity, evaluate long term implications and better target clinical intervention.
- Placebo Effect
- Heel Pain
- Free Nerve Ending
- Complex Regional Pain Syndrome Type
- Order Neuron
Foot pain is experienced by 17 to 42% of the adult population [1–4]. It is disabling in nearly half of these cases  and can impair mood, behaviour, risk of falls, self-care ability and quality of life [3, 5–11]. Foot pain is complex, and difficulties in accurately diagnosing the source of pain and cause of tissue damage can impair clinical management of the pain [12, 13]. However, most people with foot pain do not seek professional treatment, even when the pain is disabling . There is clearly a need to improve the provision of foot care to people suffering such pain.
Currently, the aetiological mechanisms underlying some types of tissue injury within the foot are not clearly understood. As a result, interventions targeting foot pain in clinical trials often lack specific targets (e.g. plantar heel pain) . Perhaps as a result of this limitation, evidence from randomised controlled trials of some common interventions that are highly regarded in clinical practice (e.g. custom foot orthoses) have detected only small, if any, beneficial effects .
A deeper understanding of pain is needed to identify the nature and mechanism of foot pain, its diagnosis and how best to target clinical intervention. It has been two decades since a review on foot pain has been published [16–19]. Given that almost all prevalence studies for foot pain have been performed since then, in addition to the recent advances in our understanding of the nature and mechanism of pain in general, a review of this type is warranted. The aim of this paper was to comprehensively review the literature on foot pain, with specific reference to its definition, prevalence, aetiology and predictors, classification, measurement and impact. We conclude by discussing the complexities of foot pain as a sensory, emotional and psychosocial experience in the context of clinical practice, therapeutic trials and the placebo effect.
Foot pain is an unpleasant sensory and emotional experience following perceived damage to any tissue distal to the tibia or fibula; including bones, joints, ligaments, muscles, tendons, apophyses, retinacula, fascia, bursae, nerves, skin, nails and vascular structures . Foot pain is a general term, inferring neither pain class, injury mechanism nor histological pathology. As further discussed in later sections, it is important to recognise that foot pain is not the noxious-stimuli-induced activity in the nociceptive pathways [20, 21], but rather the perception of these processes and the consequent effects on suffering and pain-related behaviour .
Prevalence of foot pain in randomly selected populations
Sample source and description
Foot pain prevalence
Pain outcome measure and notes
4,060 people aged ≥20 yrs (51% female) recruited by telephone interview (49% response rate) from north-western Adelaide, South Australia
Foot pain defined as affirmative response to 'On most days do you have pain, aching or stiffness in either of your feet?'
301 community-dwelling older adults (representing 31% response rate) aged 70–95 yrs (61% female) from Sydney, NSW, Australia
Disabling foot pain defined as: current foot pain, foot pain in the past month, plus at least one item marked on the Manchester Foot Pain and Disability Index .
784 community-dwelling older adults (representing 85% response rate) aged 65–101 yrs (57% female) from Springfield, Massachusetts, USA
Foot pain defined as: at least 'fairly often' foot pain in the previous week, or foot pain or discomfort 'most days' within the previous month .
3,417 community-dwelling adults (representing 84% response rate) aged 18–80 yrs (55% female) from North Cheshire and Manchester, England:
22% (9.5% disabling)
Foot pain defined as: foot pain during the past month lasting at least one day. 'Disabling' foot pain defined using the Manchester Foot Pain and Disability Index (defined above) .
135 community-dwelling older adults, all members of one private health insurance company (response rate of 28%)aged 75–93 yrs (59% female) Sydney, NSW, Australia.
Foot pain defined as: affirmative answer when asked whether they suffered from painful feet .
990 community-dwelling women (70% response rate) with a disability; aged 65 to ≥85 yrs from Baltimore, Maryland, USA
18% moderate (14% chronic and severe)
Chronic and severe foot pain defined as: 7–10 on 10-point VAS for ≥1 month within the last year and present in the previous month. Moderate foot pain defined as: 4–6 on VAS for ≥1 month within the last year, or pain rated as 7–10 on VAS lasting ≥1 month and not present within the previous month .
Tissue damage in the foot may occur via chemical, mechanical or thermal stimulation  associated with direct trauma, musculoskeletal overload, infection, or systemic or proximal pathology (e.g. nerve entrapment, diabetic neuropathy). Many common types of foot pain such as tendonitis, stress fracture, corns and callus are routinely attributed, in part or full, to mechanical stress . While mechanical stress (broadly defined as force applied to tissue) is a normal component of foot function, tissue damage occurs when the maximum stress threshold of the tissue is exceeded . This may occur with: (1) short duration, high magnitude stress; (2) long duration, low magnitude stress; or (3) repetitive moderate-magnitude stress .
Associations and predictors of foot pain
Identifying factors that predict foot pain enables the clinician to modify or prevent contributing factors and even target at-risk groups with preventative strategies and more appropriate treatments. Demographically, advancing age and female gender are associated with foot pain . However, while the prevalence of disabling foot pain has been shown to increase with age in both genders peaking at 55 to 64 years of age (15% for females and 12% for males), it has been reported to then steadily reduce with older age . In contrast, studies specifically focussing on foot pain in older adults suggest otherwise, with prevalence as high as 42% (Table 1).
Disabling foot pain appears to occur typically in association with other pain regions, including hip/leg pain, axial skeletal pain and/or shoulder pain; and is more likely to occur in patients previously diagnosed with arthritides, diabetes and/or stroke [4, 5, 10]. In the largest study to date, Garrow et al.  reported people with rheumatoid arthritis were three times more likely to report disabling foot pain, although this did not reach statistical significance due to the very small number of people included in this part of the analysis.
Garrow et al.  also reported that people in Northwest England aged 18 to 80 years with disabling foot pain were significantly more likely than people without disabling foot pain to self-diagnose nail problems (42% vs. 22%), corns and callosities (41% vs. 30%), bunions (19.5% vs. 7%), swollen feet (34% vs. 10%), flat/planus feet (9% vs. 6%), high arch/cavus feet (18% vs. 13%) and toe deformity (33% vs. 13%) (p < 0.05). Menz et al.  also reported associations between disabling foot pain and pes planus as well as limited ankle joint range of motion in older Australians. In the study be Garrow et al , however, podiatrist-diagnosed foot problems using established criteria [27–29] revealed only swollen feet as a correlate of disabling foot pain (43.7% vs 18.0%; OR: 3.8; 95% CI: 1.7 to 8.2). This unexpected result is supported by Badlissi et al. , who reported that people over 65 years of age with foot pain were no more likely than people without foot pain to have hallux valgus, pes planus or lesser toe deformity (including hammer, mallet, claw or overlapping toes and bunionette). Badlissi  did note, however, an association between foot pain and pes cavus. Discrepancies between these studies are possibly due to differences in sample characteristics and diagnostic/classification criteria.
Extrinsic factors commonly associated with foot pain include inappropriate footwear [30, 31] and occupational activities , although these areas have received little empirical investigation in the past. For both intrinsic and extrinsic factors, further research is needed to develop predictive models of foot pain causation in large prospective random samples of children, adolescents and adults.
The difficulties in clearly defining pain have impeded the development of clinically relevant pain models capable of guiding foot pain classification and communication among and between practitioners and patients [33–35]. Currently, emerging evidence of the neurological differences between physiological and pathophysiological pain is prompting the redevelopment of existing pain classification models, particularly for chronic pain, which will have implications on our understanding of foot pain [36–38]. The following section clarifies the underlying neurological differences between the many clinical presentations of foot pain, although it is important to point out that many aspects of foot pain are not mutually exclusive.
Physiological foot pain
Physiological foot pain is experienced as an acute response to injury (or potential injury) following healthy functioning of both the peripheral and central nervous systems [37, 39]. It provides a feedback system to encourage the removal of potential tissue-damaging stimuli (as per defense-response theory) [35, 37, 40]. There are three essential criteria for classification as physiological foot pain [23, 35, 37–39]: (1) noxious (potentially tissue damaging) stimuli are extrinsic to the nervous system; (2) pain perception is proportionate to the magnitude of noxious stimulation; (3) pain diminishes when the stimuli are removed. An example of physiological foot pain would be the response to a stone trapped in one's shoe or a blister from a new pair of shoes. The activity within the nervous system producing the experience of pain is termed nociception. Nociception in physiological foot pain comprises three distinct processes: transduction; transmission; and modulation.
Foot pain is the end result of a cascade of impulses originating in the stimulation of structurally unspecialised free nerve endings within foot tissue [23, 41]. These free nerve endings are called nociceptors. In response to potentially harmful mechanical, thermal and chemical stimuli, nociceptor cell membranes depolarise. If the stimulation is strong enough, ion channels within the membrane are activated; creating a self-propagating change in membrane potential that sweeps along the electrically excitable membrane cells [23, 38].
Roles of A-delta and C fibres in nociception
1 to 5 microns
< 1.5 microns
5–20 metres per second
0.5–2 metres per second
Mechanical and sometimes thermal
High intensity mechanical, thermal and chemical
Dull, throbbing, aching
Mechanisms capable of modifying the propagation of nociceptive impulses from the foot to the brain have been proposed to exist at all levels of the nervous system and to influence both sensory and emotional components of pain [35, 38, 42]. This selective projection and inhibition of impulses has been attributed in part to neural plasticity (the ability of neural tissue to regulate its own activity) . The foundations of neural plasticity were first introduced in the Melzack-Wall gate control theory of pain in 1965 . Melzack and Wall hypothesised that afferent impulses (ascending toward the brain) could be inhibited by efferent impulses (descending from the brain) in the dorsal spinal horn. Recent research has supported Melzack and Wall's hypothesis and highlighted the influence of psychosocial factors (e.g. pain beliefs) on the descending inhibition and consequent reduced experience of pain [22, 23, 36]. Modulation of nociception might account for some of the foot pain reduction experienced with the placebo effect.
Pathological foot pain
Pathological foot pain is experienced following nociceptive pathology; involving dysfunction of either or both of the peripheral or central nervous systems [37, 39]. While there is debate as to which classes of pain deserve categorisation as pathological foot pain, common suggestions include neuropathic, inflammatory and chronic pain [36, 37]. These pain classes are categorised as pathological foot pain since at least one of the three criteria for physiological foot pain is not met [23, 35, 37–39]. That is, in pathological foot pain: (1) noxious stimuli are intrinsic to the nervous system; (2) foot pain perception is disproportionate to the magnitude of noxious stimulation; and/or (3) foot pain does not diminish when the stimuli are removed. Due to such dysfunction, pathological foot pain extends far beyond the mechanistic defense response role attributed to physiological foot pain .
Neuropathic foot pain
Evocation of pain by a stimulus that does not normally evoke pain.
A spontaneous or evoked unpleasant, abnormal sensation, e.g. hyperalgesia and allodynia.
Increased pain response to a stimulus that is normally painful. Might be static, punctate or dynamic, and might occur with thermal stimuli. Suggested to be a consequence of peripheral and/or central sensitisation.
Increased sensitivity to stimulation, including diminished threshold and increased response. Excludes the special senses.
Increased threshold and abnormally painful reactions to stimuli, especially repetitive stimuli. Might occur with dysthesia, hyperalgesia, allodynia or hyperesthesia. Occurs in the presence of fibre loss.
A spontaneous or evoked, abnormal but not unpleasant sensation. Proposed to reflect spontaneous bursts of A-β fibre activity.
Spontaneous or stimuli-associated shooting, electric-shock like or stabbing pains. Might be elicited by an innocuous tactile stimulus or by a blunt pressure.
Abnormal spread of pain from a peripheral or central lesion. Typically referred from deep to cutaneous structures.
Partial or complete loss of afferent sensory function. Might not involve all sensory pathways.
Neuropathic pain is routinely sub-categorised according to the causative factor, e.g. mechanical injury, neurotropic viral disease, neurotoxicity, metabolic disease, inflammatory and/or immunologic mechanisms, focal ischaemia or neurotransmitter dysfunction . It is expected that continued advances in molecular neurobiology will expose links between sub-categories and allow for the development of a comprehensive and coherent classification system for neuropathic foot pain [39, 44].
Inflammatory foot pain
'Inflammation' describes a wide range of primarily vascular responses to tissue injury . Pain (dolor) is one of the five classic, clinical features of acute inflammation, along with redness (rubor), heat (calor), swelling (tumor) and limitation of function (functio laesa) . Inflammation produces characteristic changes within the nervous system . In early stages, inflammatory mediators activate second-messenger systems, thereby sensitising polymodal nociceptors and reducing the activation thresholds of conducting ion channels [36, 41, 54]. Within the foot, cutaneous nociceptors are sensitised to thermal stimuli and deep somatic nociceptors are sensitised to mechanical stimuli . Clinically, this can be observed as abnormally painful responses to surface temperature changes (e.g. application of ice) and/or palpation and physical movement of affected joints. During this process, 'silent' or 'sleeping' nociceptors within the foot may be activated [36, 37, 55]. Once activated, these nociceptors fire persistently to produce uninterrupted pain . Longer term, cytokine and growth factor mediated transcription is accelerated, increasing the rate of receptor production . As a result, primary hyperalgesia occurs at the site of tissue damage . These changes are frequently accompanied by sensitisation of the central nervous system and nerve damage, which may provoke neuropathic foot pain .
Chronic foot pain
Proposed definitions of chronic pain are inconsistent and difficult to use in clinical practice [34, 37]. Despite its widespread use, the term 'chronic' has been criticised for its potential to be confusingly used as a descriptor of pain history and as a prognostic statement for pain . The International Association for the Study of Pain (IASP) defines chronic pain as any pain persisting past the normal time of healing and suggests three months to be the most suitable point of division between acute and chronic pain for nonmalignant pain . Variations to this definition are common, particularly with regards to time framing [20, 37, 56].
Despite semantic disagreement, there is apparent consensus regarding clinical and underlying physiological distinctions between acute and chronic pain . Chronic foot pain does not typically share the sharp spatial localisation typical of acute foot pain. Chronic foot pain is characteristically diffuse, spreads beyond the original site of injury, exhibits a non-linear relationship between nociception and pain intensity, and involves adaptive changes at various levels of the nervous system, e.g. activation of propriospinal reflexes, which play a role in coordination, posture and locomotion [21, 35, 41].
Clinically, it is important to recognise that chronic foot pain is pain persisting past the normal time of healing following the removal of the noxious stimulus . Chronic foot pain is not simply pain persisting past an arbitrary time point (e.g. three months). If the stimulus has not been removed, the pain should not be termed chronic.
Changes in foot pain perception with age
In recent years, several comprehensive reviews have discussed age-related changes in pain perception [57, 58]. Whilst there is some contradiction between empirical findings, most studies demonstrate age-related increases in pain threshold (the least amount of stimulation required for a person to experience pain) using heat or mechanical stimulation, but not from electrical stimulation . The decline in heat pain sensitivity is most noticeable after 70 years of age and may be more pronounced in the distal extremities . Pressure pain threshold increases by about 15% and is more noticeable in females than males . Heat pain threshold increases by about 20% for radiant pain and 50% to 100% for CO2 laser pain [59, 62].
Whilst there appears to be a modest age-related increase in pain threshold and diminished sensitivity to low levels of noxious stimulation, response to higher intensity stimuli is increased and tolerance of strong pain is reduced . Recent experimental studies suggest this may stem from alterations in peripheral A delta and C fibre nociception and central nervous system changes, including reduced central nervous system plasticity following injury and reduced efficacy of endogenous analgesic mechanisms .
There is currently no universally accepted standard for the measurement of pain . As a result, numerous quantitative and qualitative pain measurement tools have been developed. Since pain is a subjective sensory and emotional experience, the participant's own reporting of pain is widely regarded as the most valid representation of their pain . As such, self-reported pain intensity is the most frequently used research tool to measure pain [44, 64]. Popular tools include visual analogue scales (VAS), numerical rating scales and verbal category/Likert scales [44, 64, 65]. Tools used to measure foot pain include the: Foot Function Index ; Foot Health Status Questionnaire , physical health domains of the Diabetes Foot Ulcer Scale ; Manchester Foot Pain and Disability Index ; Rowan Foot Pain Assessment Questionnaire ; American Academy of Orthopaedic Surgeons Foot and Ankle Questionnaire . Across all these tools, the individual's subjective reporting of pain is regarded as a valid representation of their pain . However, criticism of pain intensity outcome measures have concluded that: people preferentially use the beginning, middle and end of continuous pain scales (e.g. VAS) ; there are specific clinical attributes of pain class not always captured in generic tools (e.g. chronic/inflammatory/neuropathic) ; the fluctuating nature of many pain conditions are often inappropriately disregarded ; the results of intervention trials are often difficult to interpret due to unknown or unspecified clinically important differences detected by the pain measurement tool used .
Despite these limitations, foot pain as an outcome measure has much to offer clinical practice and research . It is important, however, to ensure that pain reduction does not dominate health outcome assessment in clinical practice. Jensen et al.  suggest that pain reduction has dangerously been equated with therapeutic success, leaving many other clinically relevant health outcomes overlooked, e.g. functional ability.
The broader impact of pain in the community
Inability to pursue hobbies among children and adolescents 
School absenteeism among children and adolescents 
Fear of movement and re-injury in chronic musculoskeletal pain 
Interpersonal strain due to behavioural changes among children and their families 
Increases severity of depressive symptoms 
Impairs recognition of depression 
Impairs adherence to medication if coinciding with depression 
To gauge the full impact of foot pain on one's life, it can be useful to measure health-related quality of life. Health-related quality of life is an individual's health status encompassing any aspect of life affected by mental and physical well being . In recent years, health-related quality of life has been increasingly promoted as one of the most important outcomes for the evaluation of therapeutic interventions for pain [88, 96, 97]. Pain has a detrimental effect on all aspects of health-related quality of life, spanning all age groups, pain types and pain sources . Of clinical importance is that health-related quality of life is reduced most when pain is of long duration and high intensity . From a study of 81 chronic pain sufferers, Dysvik et al.  identified five predictors of poor health-related quality of life in chronic pain sufferers: (1) female gender; (2) longer pain duration; (3) greater pain intensity; (4) a view of pain as mysterious; and (5) less social support. Clinically, it might be beneficial to address the modifiable predictors: pain intensity (e.g. by therapy); view of pain as mysterious (e.g. by education); and less social support (e.g. by providing contacts for local support networks).
Some specific tools used to measure health-related quality of life in foot pain research include: four domains of the 36-Item Short-Form Health Survey (physical functioning, general health, vitality, and social functioning) ; the Quality of Life subscale of Foot & Ankle Outcome Score ; and the Health-Related Quality of Life Index . Evidence from randomised controlled trials demonstrates that effective treatment of foot pain can lead to clinically important improvements in health related quality of life .
In this review of foot pain, we have discussed its prevalence, aetiology and predictors, classification, measurement and impact. We have also described the complexities of foot pain as a sensory and emotional experience and how the psychosocial context can influence treatment response to produce a 'placebo effect'. It is hoped that this paper will provide a platform from which to advance the diagnosis and treatment of foot pain in clinical practice and its evaluation in clinical trials.
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