Risk Factors for the Development of Plantar Heel Pain Syndrome - A Literature Review

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Top Contributors - Merinda Rodseth, Kim Jackson, Jess Bell and Tarina van der Stockt  

Introduction

Many factors have been proposed as risk factors for the development of Plantar Heel Pain Syndrome (PHPS). These include limited ankle dorsiflexion, obesity, pes planus (excessive foot pronation), occupations requiring prolonged periods of standing, pes cavus (high foot arch), increased plantar fascia thickness, leg length discrepancy, heel pad thickness, muscle imbalance, limited range of motion of the first metatarsophalangeal joint, calcaneal spur, heel neuroma, inferior calcaneal exostosis, entrapment neuropathies, foot posture, abductor hallucis morphology, excessive running, sedentary lifestyle, age, gender, running variables such as surface, speed, frequency and distance per week, improper shoe fit and wear, sports activity, etc (Rome 2001, McPoll 2008, Irving 2006, Crawford 2009, Valizadeh 2018, Landorf 2021, Hogan 2019, Mens 2019, Trojan 2019, Allam 2021, Sullivan 2020).

There are numerous research studies about PHPS but not all research studies are of equal quality and it is therefore important to keep the criteria of  good-quality studies in mind when reading the literature:

• An adequate sample size of more than 30 participants
• Randomisation of participants and the presence of a matched control group

For ease of understanding, the literature review of the risk factors for PHPS will be divided into three different categories: (Saban talk 2021, Menz 2019, Sullivan 2020)

• Intrinsic factors specific to the foot  
• Intrinsic factors related to the anatomy or biomechanics of the individual
• Extrinsic factors related to external influences acting on the foot

The following intrinsic and extrinsic factors will be discussed in more detail (Figure 1):

Figure 1. Risk factors proposed to be associated with PHPS (Intrinsic foot level factors - dark blue, Other intrinsic factors - light blue, Extrinsic factors - green)

Intrinsic foot-level factors

A variety of factors intrinsic to the foot are considered as potential risk factors for the development of PHPS and will be further explored. These include:

Calcaneal Spur

Calcaneal spur (enthesophyte) refers to “an abnormal bone outgrowth at the inferior part of the calcaneus” often from the attachment site of the plantar fascia ligament (Alatassi 2018). Calcaneal spur is considered to be a common cause of heel pain but it is difficult to define what should be considered a pathological spur and it remains controversial whether the calcaneal spur actually contributes to the symptoms of plantar heel pain (PHP) (Alatassi 2018, Ahmad 2016). Many researchers disagree about the site and aetiology of calcaneal spurs and whether it is a cause of PHP, as many patients also present with painless plantar heel spurs (Ahmad 2016).  While studying the relationship between plantar heel spurs and plantar fasciitis, Ahmad et al (2016) classified plantar heel spurs based on their morphology into 4 shapes: 0 or absent, 1 or horizontal, 2 or vertical and 3 or hooked, with type 1 (horizontal) being the most prevalent (60.6%).  Zhou et al (2015) classified calcaneal spurs into 2 types based on their anatomical location as found in patients with plantar fasciitis as Type A (superior to the plantar fascia) and Type B (from the plantar fascia insertion and within the plantar fascia).

Calcaneal spurs are often regarded as incidental products of the same risk factors causing PHP and coexisting with PHP (Moroney 2014, Menz 2019). Moroney et al (2014) however found that patients with calcaneal spurs are more than twice as likely to have foot pain than individuals without spurs and the prevalence of heel spurs increased with:

• Advancing age
• Female gender
• Obesity
• Diabetes mellitus
• Osteoarthritis (Maloney 2014)

The connection between calcaneal spurs and PHPS is still not clear but studies are showing that calcaneal spurs might not be merely incidental and that the presence of plantar calcaneal spurs does matter. Figure 2. Large calcaneal spur

Heel pad

The subcutaneous layer of adipose tissue underneath the calcaneus on the heel is known as the heel fat pad. It is designed to provide cushioning and shock absorption to the underlying calcaneus during weight-bearing (Rodriquez 2019, Khatiwada 2019). Changes to the mechanical properties of the heel fat pad have been proposed to be associated with the development of PHP (Rodriquez 2019). Local trauma, advancing age and overuse may cause changes in the structure of the heel pad, including a reduction in thickness, diminishing its compressibility and shock-absorbing capacity and leading to diffuse heel pain (Saban talk 2021, Rodriquez 2019). Many studies have analysed the relationship between heel pad thickness and PHP with varying results (Figure 3).

Figure 3. Heel pad thickness in heel pain (Saban 2021)

No conclusive evidence, therefore, exists that the heel fat pad can contribute to heel pain.

Plantar Fascia Thickness

Plantar fasciitis has long been considered a significant cause of PHP (Valizadeh 2018).  Histopathological changes in the plantar fascia taken from surgical biopsy confirm a range of degenerative processes resulting in collagen breakdown, fibrocyte cell population changes (including death), matrix degradation and vascular ingrowth, and these appear to represent a similar process observed in the tendinopathy continuum (Saben talk 2). Imaging studies have indicated an association between PHP and thickening of the plantar fascia (Menz 2019). Wall et al (1993) suggested that a plantar fascia thickness of more than 4.0mm would be consistent with plantar fasciitis as a general rule. This has subsequently been accepted as the general guide for plantar fascia thickening. Numerous studies found that patients with heel pain presented with thickened plantar fascia of more than 4 mm compared to asymptomatic individuals (Figure 4).

Figure 4. Evidence on plantar fascia thickness

A link between increased plantar fascia thickness and PHPS has therefore been established (Saban 2021 talk, Menz 2019).

Intrinsic Factors Related to the Anatomy or Biomechanics of the Individual

Alternative intrinsic factors not inherent to the foot but related to the anatomy and biomechanics of the individual can also be potential risk factors for the development of PHP (Hogan 2019, Sullivan 2020, Saban talk 2021). These can include:

Posture and Alignment of the Ankle and Foot

Posture and alignment of the foot have long been considered significant in the development of PHP (Sullivan 2020). Many factors concerning the posture and alignment of the foot and ankle have been implicated in PHP and include: (Sullivan 2020)

• Longitudinal arch height - both a low-arched foot (pes planus) and a high-arched foot (pes cavus)
• Calcaneal angle/alignment
• Limited range of motion (ROM) of the 1st metatarsophalangeal joint (MTPJ)
• Toe flexor strength deficits

A summary of the findings from numerous studies on the posture and alignment of the foot and ankle can be found in Figure 5. (Allen 2003, Labovitz 2011, Wenzel 2009, Taunton 2002, Werner 2010, Ribeiro 2011, Fessel 2014, Irving 2007)

Figure 5. Postural factors associated with PHPS

Image: Alvinjiaodi, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Content: Slide from Saber 2021

There is therefore insufficient evidence to support the view that clinical and biomechanical findings of the foot and ankle function affect PHPS.

Posture and Alignment of the Knee

Posture and alignment of the knee have also been proposed as possible risk factors for the development of PHPS and studies produced varied results (Figure 6). (Labovitz 2011, Mahmood 2010, Taunton 2002) Figure 6. Posture and alignment of the knee

Image: BioMed Central, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

Content: Saban B. Literature review of risk factors for PHPS. Physiopedia course. 2021.

There is therefore currently no evidence of a link between posture or alignment of the knee and PHPS.

Limitation of Ankle Joint Dorsiflexion

Limited dorsiflexion range of the ankle is often proposed as a risk factor for plantar heel pain (Sullivan 2020). A lack of dorsiflexion during the stance phase of the gait cycle is postulated to lead to a compensatory increase in midfoot dorsiflexion, lowering the arch of the foot and increasing tensile load on the plantar fascia (Sullivan 2020). A continuous connection between the plantar fascia and Achilles tendon has been described in anatomical studies, and it is proposed that in individuals where this link exists, the increased tensile load in the gastrocnemius-soleus complex following inflexibility could be directly transmitted to the plantar fascia (Sullivan 2020). Many studies have investigated the relationship between limited ankle joint dorsiflexion and PHPS with conflicting results (Figure 7) (Kibler 1991, Rome 2001, Porter 2002, Riddle 2003, Irving 2007, Wenzel 2009, Bolivar 2013, Sullivan 2015, Lee 2021, Landorf 2021).

Figure 7. Ankle Dorsiflexion limitation

As can be seen from these studies, there is no agreed evidence that limited ankle dorsiflexion range is associated with the development of PHPS.

Dynamic Foot and Ankle Motion

When individuals walk or run, the plantar aspects of the feet are subjected to considerable forces during the ground contact phase of each step. The heel is often the first part of the foot to strike the ground and large forces are generated by the impact (Bennett 1990). The heel strike phase of the gait cycle, therefore, represents heavy loading for the heel pad tissues (Saban 2021). Heel strike is seen as a short spike of force (typically 10-20 ms), superimposed on the upslope of the ground reaction force (GRF), immediately following initial foot contact (Saban 2021). The initial peak during the stance phase on a graph representing the vertical ground reaction force produced by an individual walking depicts the initial force produced during heel contact, whereas the later force peak is produced by the more distal parts of the foot. (Figure 8).

By Jenna Fair - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=28572903

Figure 8. Vertical Ground reaction forces during walking

The functioning of the foot changes during the dynamic actions of gait and running resulting in increased pressure on the plantar aspect of the foot as well as changes in the plantar pressure distribution (Ribeiro 2011). It has therefore been proposed that individuals with plantar fasciitis would present with altered ground reaction forces and patterns of plantar pressure distribution   (Ribeiro 2011). Ribeiro et al (2011) found no changes in plantar pressure distribution patterns in recreational runners with plantar fasciitis when compared to control runners. Pain also did not interfere with the dynamic patterns of the plantar pressure distributions (Ribeiro 2011). Chang et al (2014) found that when compared to healthy controls, individuals with plantar fasciitis exhibited significantly

• Greater total rearfoot eversion
• Greater forefoot plantar flexion at initial contact
• Greater total sagittal plane forefoot motion
• Greater maximum dorsiflexion of the 1st MTPJ
• Decreased vertical GRF during propulsion

Controversially, Bovonsunthonchai et al (2019) reported that adaptations in intra-foot motion showed a reduction in some angles but no significant differences in GRF between individuals with plantar fasciitis and healthy individuals when walking at a similar gait speed.

There is therefore no conclusive evidence that a change in walking dynamics exists in individuals with PHPS.

Plantar Flexion Endurance

Reduced calf muscle (plantar flexion) endurance has also been postulated as a risk factor for PHPS (Irving 2007, Sullivan 2015, Sullivan 2020). Two studies have however reported no relationship between plantar flexion endurance and PHP as can be seen in Figure 9 (Sullivan 2015, Irving 2007).

Figure 9. Plantar flexion endurance

Reduced plantar flexion endurance is therefore not likely to be associated with PHPS.

Body Mass Index

Body mass index (BMI) is an expression of weight compared to height and is classified as: (Valizadeh 2018)

• Underweight: < 18.5 kg/m2
• Ideal weight: 18.5 -24.9 kg/m2
• Overweight: 24.9 - 29.9 kg/m2  
• Obese: >30 kg/m2

BMI has been associated with alterations in foot posture and is proposed as a risk factor for PHPS (Sullivan 2015, 2020, Menz 2019). Many studies investigating PHPS found that individuals with PHP had a higher BMI and were middle-aged  (Figure10) (Rome 2001, Rompe 2005, Baldassin 2009, Porter 2002, Sullivan 2015, Landorf 2006, Moroney 2014, Saban 2014). Figure 10. Body Mass Index compared to age

The relationship between body mass index (BMI) and PHPS has been extensively studied and a consistently strong clinical association between increased BMI and PHPS has been reported (Van Leeuwen 2016, Butterworth 2012, Valizadeh 2018, Menz 2019).

Extrinsic Factors Related to External Influences Acting on the Foot

Environmental and circumstantial influences acting on an individual are collectively known as extrinsic factors and include: (Irving 2007)

• Prolonged standing
• Inappropriate shoe fit
• Previous injury
• Running surface, speed, frequency and weekly distance.

Evidence is limited for most of these factors and the role they play in the development of PHPS not well understood (Irving 2007).

Activities Related to Sports

It has long been debated whether participation in sports leads to PHPS or if it is protective against PHPS. Many individuals with PHPS reported not participating in sports which were reported to put them at risk for PHPS (Saban 2014, Rano 2001). The lack of participation in regular exercise has been associated with an increased prevalence of plantar fasciitis whereas physical activity 3 times/week for more than 20 minutes was associated with a decrease in prevalence, positioning participation in sports as protective against PHPS (Van  Leeuwen 2002).

Yet, even though PHPS is more common in sedentary individuals, those who participate in sport do also experience PHP, raising the question of whether it could also lead to PHPS.

In a study by Di Caprio et al (2010) 31% of 166 runners reported one or more episodes of plantar fasciitis preventing them from running for more than 2 weeks. The incidence of plantar fasciitis was statistically related to (Figure 11):

• Years of activity
• Days of practice per week (>6 days/week)
• Number of kilometres per week (>60 km/week)
• Athlete’s height

Figure 11. Factors affecting the occurrence of plantar fasciitis in runners (Di Caprio 2010)

For these athletes, no statistically significant relationships were found between age, weight and BMI (Di Caprio 2010).

Even though a strong association exists between increased BMI and PHPS in the non-athletic population (Butterworth 2012), there appear to be 2 distinct populations affected by PHP - sedentary individuals with a higher BMI and athletes with the correct BMI and high activity level (Van Leeuwen 2016) (Figure 12). Figure 12. Relationship between PHPS, BMI and sport

As far as the evidence is concerned, participation in sports appears to protect against PHPS but prolonged intense activity can also become the cause of PHPS.

Activities Related to Standing Time

Prolonged standing is often proposed as a risk factor for the development of PHPS. Standing time is however not easy to assess and different methods have been used between studies to assess its impact with most studies reporting no significant relationship between standing time and PHPS (Figure 13) (Alvarez 2000, Taunton 2002, Riddle 2003, Irving 2007, Werner 2010, Sullivan 2015).

Figure 13. Evidence for the relationship between standing time and PHPS (Bernice talk)

Mental Health

An association between psychological disorders and musculoskeletal pain has been firmly established by numerous studies (Cotchett 2016, Shivarathre 2014, Drake 2018). Psychological factors, such as anxiety, depression and stress, have been identified as strong risk factors for pain and disability (Shivarathre 2014, Drake 2018). In the foot and ankle, an association was also found between anxiety, depression and chronic foot and ankle pain (Drake 2018, Shivarathre 2014). Cotchett et al (2016) also reported symptoms of depression, anxiety and stress to be independently associated with PHP. This association was also found in the foot and ankle (Figure 14) (Shivarathre 2014, Cotchett 2016, Drake 2018).

Figure 14. Studies on the association between mental health and PHPS (Saban 2021)

A link does therefore exist between mental health and PHPS, even though it might not be the main cause of PHPS.

Conclusion

PHPS is a complex, multifactorial condition that affects various tissues (Menz 2019). Many intrinsic and extrinsic factors are proposed to be associated with the development of PHPS, many with inconsistent results. Of all the risk factors assessed, only plantar fascia thickness, increased BMI and to some extent, mental health, has been consistently associated with PHPS.

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