Association of Obesity and Plantar Fasciitis in Patients With Plantar Heel Spurs

Abstract

Background:

Although its pathophysiology is not clear, the presence of a plantar heel spur has been considered a cause of heel pain in plantar fasciitis. This study investigated demographic and radiographic differences between a plantar fasciitis patient group with plantar heel spur and the age/sex-matched control group with plantar heel spur.

Methods:

Patients who visited the office under the diagnosis of plantar fasciitis and had a plantar heel spur were compared to an age/sex-matched control group who visited the office with other foot and ankle issues except for heel pain. All patients in both the control and case groups had radiographically proven presence of a plantar heel spur. Demographics and radiographic findings between the 2 groups were compared, and a multivariable logistic regression analysis was performed to identify independent risk factors that are associated with plantar fasciitis symptoms.

Results:

A total of 100 patients were included in the plantar fasciitis study group (PF+S) and age/sex-matched control group (C+S). BMI was higher in the study group than in the control group: 35.2 vs 30.9 (P = .002). The size of the plantar heel spur was larger in the study group than in the control group: 5.9 vs 4.6 mm (P = .017). A multivariable regression analysis identified that obesity (BMI > 30, odds ratio [OR] = 2.675) and the size of plantar heel spur >5.3 mm (OR = 2.642) were associated with PF+S.

Conclusion:

We found an association of both obesity and increased average plantar heel spur length on lateral radiographs in patients with painful plantar fasciitis compared to patients without plantar fasciitis but with plantar heel spurs. The presence of a plantar heel spur alone did not account for the symptoms of plantar fasciitis.

Level of Evidence:

Level III, comparative case study.

Introduction

Plantar fasciitis is one of the most common reasons for plantar heel pain. The prevalence of this condition has been reported in 10% of the general population, and it has been estimated to affect approximately 2 million people in the United States each year.^6,33 Although it is relatively more common in active athletes or military personnel, ²⁶ plantar fasciitis can occur in those who have a sedentary lifestyle as well. With its high prevalence, plantar fasciitis causes a negative impact on functional activities and quality of life.^12,26,27

The exact etiology of plantar fasciitis is still uncertain, and the pathogenesis is likely multifactorial. These include degenerative changes like heel pad atrophy and arthritis, patient factors such as increasing age, obesity, and their medical conditions such as inflammatory arthropathy.^2,13,26 Extrinsic factors including inadequate footwear cushioning, inappropriate medial arch support, and prolonged weightbearing should be considered also. ⁴ Several theories have been proposed to explain the causes of pain in patients with plantar fasciitis; they include plantar heel spurs, periosteal inflammation, increased calcaneal intraosseous pressure, nerve entrapment, and chronic inflammation and microtrauma to the plantar fascia.^7,9 Among these, plantar calcaneal bone spur has received substantial attention as a major etiology of pain from plantar fasciitis although there is no proven causality between them.

The incidence of plantar heel bone spurs has been reported in 45% to 85% of patients with plantar fasciitis and 10% to 63% of asymptomatic patients. ²² With evidence of its high incidence in patients with plantar fasciitis, several authors insist that the plantar heel spur is a contributory source of pain. ¹⁷ This is also supported by the high success and patient satisfaction rate following calcaneal bone spur removal procedure. ⁹ On the contrary, some studies showed large numbers of patients with painless plantar heel spur,^22,23 or painful plantar fasciitis without plantar heel spurs. ²⁵ Furthermore, several anatomic and magnetic resonance imaging (MRI) studies showed evidence against an association between plantar heel spur and plantar fasciitis.^1,3,18,19,28

The purpose of this study is to investigate the demographic and radiographic differences between plantar fasciitis study group with plantar heel spur (PF+S) and age/sex-matched control group with plantar heel spur (C+S) and identify risk factors that are associated with plantar fasciitis through a multivariable logistic regression analysis.

Methods

This age/sex-matched case-control study was conducted by retrospectively reviewing medical records and radiographic images of patients who visited the office under the diagnosis of plantar fasciitis (International Classification of Diseases, Tenth Revision, code of M72.2) over an 18-month time span. The clinical diagnosis of plantar fasciitis was based on the patient’s history such as heel pain, any activity-related medial heel pain, and physical examination findings including tenderness at medial calcaneal tuberosity. Exclusion criteria included (1) pediatric and adolescent patients, whose age is <18 years, (2) any surgical history of plantar fasciitis, (3) recent history of heel trauma in 6 months, (4) history of local corticosteroid injection for the treatment of plantar fasciitis in 6 months, (5) Ledderhose disease, (6) Charcot arthropathy, and (7) no calcaneal heel spur present. Plain radiographs of the lateral view of the foot or ankle were reviewed for all patients. Initially, a total of 76 patients with the diagnosis of plantar fasciitis were identified. All of them were reviewed, and only patients who had plantar heel spur were extracted. Fifty of 76 patients who met the inclusion and exclusion criteria were finally included in the study group (PF+S). There were 3 patients who had bilateral foot plantar fasciitis; all of them were included in this study, but only 1 side that had worse symptoms was calculated as 1 case. Patient demographics such as age, sex, body mass index (BMI), medical comorbidities including diabetes mellitus, smoking, rheumatoid arthritis, or any lower extremity arthritis were reviewed. Arthritis was counted if patients had history of a lower extremity joint replacement or any history of lower extremity arthritis including knee, hip, or foot and ankle.

This study was designed to have 1:1 matching with the criteria of sex and age (within 2 years). The control group (C+S) was identified for those who visited the office with other foot and ankle issues except for heel pain in the same period of the study. All patients in the control group had plantar heel spur but did not have heel pain or a diagnosis of plantar fasciitis. Patients with any Achilles tendon disease or injury were excluded from the control group because Achilles tendon pain might affect plantar heel pain because of the anatomical connection between the Achilles tendon, calcaneus, and plantar fascia. The following diagnoses were included for selection of the control group in this study: ankle instability, forefoot disorders like hallux rigidus or hallux valgus, and foot and ankle tendinopathy except for Achilles tendon.

Outcome Assessment

The size of plantar heel spur was measured to evaluate the effect of the size of plantar heel spur on heel pain between the 2 groups. Plantar heel spur length was measured on a lateral foot or ankle radiograph using the measuring tool within the hospital PACS system (Figure 1). Furthermore, the incidence of posterior heel spur in both groups was investigated. All radiographs were independently evaluated by 2 evaluators, and their measurements of heel spur size were recorded. This accounted for the interobserver radiographic data collection component of the study. The same foot and ankle radiographs were again reviewed by the same 2 evaluators after a 1-month interval. The measurements were repeated, and the values were assessed to account for intraobserver variance. The mean value of the 2 observers’ measurements were used for the bone spur size in this study. All data including patient demographics and radiographic findings were compared between the 2 groups, and a multivariable logistic regression analysis was performed to identify independent risk factors that make plantar heel spur painful. The intraclass correlation coefficient (ICC) was used to quantify the degree of correlation between the same measurements for the size of plantar heel spur on radiographs. To interpret the ICC values, ICC values <0.5 are indicative of poor reliability, values between 0.5 and 0.75 indicate moderate reliability, values between 0.75 and 0.9 indicate good reliability, and values >0.90 indicate excellent reliability. ²⁴

Figure 1.

Plantar heel spur size measurement. Line AB: Connects ends of the plantar heel curvature, and represents the base of the heel spur. Line CD: Distance from C (line AB or base of plantar heel spur) to the most distal point of the bone spur (D), giving the size of plantar heel spur in millimeters.

Statistical Analysis

All statistical analyses were performed with SPSS software (version 21.0; IBM, Armonk, NY, USA). Data are presented as the mean and SD. Continuous variables such as age and overall BMI were compared using Student t test, and categorical variables were compared using χ² test or Fisher exact test. Variables that can have an effect on heel pain were investigated, and they were included in a multivariable logistic regression analysis to identify independent predictors of painful plantar heel spur. The level of statistical significance was set as P <.05.

Results

A total of 50 patients were enrolled in the study group (PF+S), and an equal number of patients were included in the age/sex-matched control group (C+S). The mean age was 52.7 years and 52.9 years in the study group and the control group, respectively. Of the 50 patients in each group, 15 were male (30.0%) and 35 were female (70.0%). Patient demographic data are shown in Table 1. BMI was significantly higher in the study group compared with the control group: 35.2 in the study group vs 30.9 in the control group (P = .002). The patients were categorized into subgroups based on the different BMI criteria as follows: overweight (BMI ≥ 25), obesity (BMI ≥ 30), and severe obesity (BMI ≥ 35). More overweight, obese, and severely obese patients were noted in the study group compared to the control group with a significant statistical difference (P = .046 in the subgroup of overweight, P = .021 in the subgroup of obesity, and P = .032 in the subgroup of severe obesity).

Table 1.

Patient Demographics of the 2 Groups.

Variables	Study Group (Painful Heel)	Control Group (Nonpainful Heel)	P Value a
Patients, n	50	50
Age, y, mean ± SD (range)	52.7 ± 11.5 (25.0-84.0)	52.9 ± 11.4 (26.0-82.0)	.924
Sex, n (%)			>.999
Male	15 (30.0)	15 (30.0)
Female	35 (70.0)	35 (70.0)
Laterality, n (%)			>.999
Right	25 (50.0)	25 (50.0)
Left	25 (50.0)	25 (50.0)
BMI, mean ± SD (range)	35.2 ± 7.7 (22.9-61.2)	30.9 ± 5.7 (21.8-47.3)	.002
Overweight: BMI >25, yes/no, n	48/2	42/8	.046
Obesity: BMI >30, yes/no, n	38/12	27/23	.021
Severe obesity: BMI >35, yes/no, n	21/29	11/39	.032
Diabetes mellitus, n (%)	7 (14.0)	9 (18.0)	.585
Smoking, n (%)	3 (6.0)	7 (14.0)	.182
Rheumatoid arthritis, n (%)	2 (4.0)	1 (2.0)	>.999
Lower extremity arthritis history (ankle, knee, hip), n (%)	8 (16.0)	5 (10.0)	.372

Abbreviation: BMI, body mass index.

^aBoldface indicates significance (P < .05).

Patient radiographic data including the size of plantar heel spur and the presence of posterior heel spur is shown in Table 2. The mean size of heel spur was larger in the study group (PF+S) than the control group (C+S) with a significant statistical difference (P = .017). Posterior heel spur was present in 32.0% (16 of 50) in the study group and 34.0% (17 of 50) in the control group without a significant statistical difference (P = .832). When the patients were stratified into subgroups according to the size of plantar heel spur as follows: 0 to 5 mm, 5 to 10 mm, and >10 mm, there was no significant difference between the study and control group. Table 3 demonstrates intraobserver and interobserver variability for plantar heel spur size measurements. Intraobserver agreement rates for the study and control group were excellent in observer 1 and observer 2. Interobserver agreement rates were excellent for the study and control group in the first measurement and the second measurement. Interobserver agreement rates in the mean value between the first and second measurement for the study and control groups were also excellent.

Table 2.

Patients’ Radiographic Findings Between the 2 Groups.

Variables	Study Group (Painful Heel)	Control Group (Nonpainful Heel)	P Value
Plantar heel spur size, mm (range)	5.9 ± 2.8 (1.1-13.2)	4.6 ± 2.6 (0.4-11.6)	.017 a
Presence of posterior heel spur, n (%)	16 (32.0)	17 (34.0)	.832

^aBoldface indicates significance (P < .05).

Table 3.

Intraobserver and Interobserver Variability for Plantar Heel Spur Size Measurements.

	Study Group (Painful Heel) ICC (95% CI)	Control Group (Nonpainful Heel) ICC (95% CI)
Intraobserver variability
Observer 1: first measurement vs second measurement	0.991 (0.985, 0.995)	0.983 (0.970, 0.990)
Observer 2: first measurement vs second measurement	0.994 (0.989, 0.997)	0.946 (0.905, 0.969)
Interobserver variability between observer 1 and 2
First measurement	0.963 (0.936, 0.979)	0.926 (0.867, 0.958)
Second measurement	0.977 (0.959, 0.987)	0.978 (0.961, 0.988)
Mean value between the first and second measurement	0.973 (0.953, 0.985)	0.969 (0.942, 0.983)

Abbreviation: ICC, intraclass correlation coefficient.

To identify independent risk factors that are associated with plantar heel spur painful, a multivariable regression analysis was conducted (Table 4). The mean value of plantar heel spur size for all patients in this study was 5.3 mm, which was utilized as a criterion about the heel spur size for this analysis. Obesity (BMI > 30; odds ratio = 2.675) and plant heel spur greater than 5.3 mm (odds ratio = 2.642) were identified as independent risk factors to predict painful plantar heel spur in our study.

Table 4.

Multivariable Regression Analysis Identifying Independent Risk Factors of Painful Heel.

Variables	P Value	OR (95% CI)
Obesity (BMI >30) (reference: obesity)	.028 a	2.675 (1.111, 6.443)
Diabetes mellitus (reference: yes)	.384	0.589 (0.179, 1.939)
Smoking (reference: yes)	.403	0.513 (0.107, 2.452)
Rheumatoid arthritis (reference: yes)	.493	2.501 (0.182, 34.315)
Lower extremity arthritis history (reference: yes)	.416	1.729 (0.462, 6.471)
Presence of posterior heel spur (reference: yes)	.294	0.597 (0.228, 1.563)
Plantar heel spur size (reference: 5.3 mm)	.022 a	2.642 (1.153, 6.053)

Abbreviations: BMI, body mass index; OR, odds ratio.

^aBoldface indicates significance (P < .05).

Discussion

There are patients who have painful heel without plantar heel spurs, while there are those who have plantar heel spurs without heel pain. This study started from the curiosity of the association of plantar heel pain and plantar heel spur, and our results showed that patients diagnosed with plantar fasciitis with plantar heel spur (PF+S) had significantly elevated BMI compared to the control group that also had plantar heel spur (C+S). Obesity (BMI > 30) and large size of plantar heel spur >5.3 mm were identified as independent factors associated with painful plantar heel spur. To our knowledge, this is the first age/sex-matched case control study to investigate independent risk factors of painful heel spur through a multivariable logistic regression analysis.

Johal and Milner ¹³ reported that plantar heel spur occurred in 89% of patients with plantar fasciitis compared with 32% in age/gender-matched asymptomatic control cohort. Although plantar heel spurs are more commonly seen in patients with plantar fasciitis, the relationship between plantar heel spurs and plantar heel pain is not certain. Some authors reported that plantar heel spur is a primary cause of plantar heel pain in plantar fasciitis,^8,13 whereas others believe that plantar heel spur is a result of steady traction force along plantar fascia resulting in chronic inflammation, periostitis, and osteogenesis of the bone spur. ³¹ There is no consensus that plantar heel spur is the reason for heel pain or just the result of chronic traction or vertical force at the medial calcaneal tuberosity in plantar fasciitis.

The pathophysiology of a plantar heel spur is also not completely understood. Many people believe that the apex of the plantar heel spur lies within the origin of the plantar fascia, whereas other studies have found that it lies deeper than the plantar fascia, close to the first layer of the foot intrinsic muscles, including the flexor digitorum brevis muscle and abductor hallucis, or the second layer including quadratus plantae.^{1,10,14,19,28} Traditionally, plantar heel spur formation has been explained by chronic longitudinal repetitive traction of the origin of the plantar fascia into the calcaneus. However, the veracity of this theory has been called into question because it fails to account for the recurrence of plantar heel spurs after surgical release of the plantar fascia, as well as the vertical orientation of plantar heel spur observed in anatomy studies. Smith et al ²⁸ investigated the anatomic and histopathologic features of the inferior heel spur in which 5 patients underwent open heel surgery for recalcitrant heel spur pain. The presence of a fracture through the spur was noted in 3 of 5 subjects, and osteochondral ossification was observed at the margins of a proportion of the spurs, which is a significant feature of long bone fracture healing. A histologic study by Li and Muehleman ¹⁸ indicated that the bony trabeculae of plantar heel spur was vertically oriented. The vertically oriented trabeculae can be explained as an adaptive response to repetitive stress of vertical loading on the heel. Kumai and Benjamin ¹⁵ reported that the plantar calcaneal spurs develop in response to repetitive compression rather than traction. Furthermore, several previous studies reported that vertical heel pressure during gait was strongly associated with body weight.^11,20 Our result showed elevated BMI was the independent predictor of PF+S. This finding lends support to the hypothesis that the pathophysiology of plantar heel spurs may involve vertical stress, given that higher body weight results in increased pressure on the heel. With these findings, we could suggest more protection and cushioning for the plantar heel and decrease BMI to lessen axial loading for treatment of painful heel spur in plantar fasciitis.

Previous studies reported higher incidence of plantar calcaneal bone spur in obese people compared to non-obese people.^21,22 Menz et al ²¹ investigated an association between elevated BMI and calcaneal spur in their study. Their cohort population was only for older people between 62 and 94 years, and their inclusion criterion was not painful heel like plantar fasciitis, but they recruited participants who were taking part in another study on the effect of osteoarthritis on balance and falls. Although their study population differs from ours, they demonstrated that calcaneal spurs were common in patients related to obesity. In our study, we focused on identifying risk factors of heel pain for those who had plantar fasciitis with plantar heel spur. The results confirmed that significantly higher BMI was found in the plantar fasciitis cohort with plantar heel spur compared to the control cohort. Furthermore, obesity was identified an independent predictor of painful plantar heel in the multivariable logistic regression analysis. Consistent with our findings, Butterworth et al ⁵ reported in their systematic review that increased BMI was strongly associated with chronic plantar heel pain in a nonathletic population. A retrospective study by Valizadeh et al ²⁹ demonstrated that high BMI was a strong risk factor in recurrence of chronic plantar heel pain.

There is no strong consensus regarding the association between the size of plantar heel spurs and pain in plantar fasciitis. Ahmad et al ² evaluated the severity of plantar fasciitis using MRI and showed that patients with absent or smaller spurs had significantly worse plantar fasciitis on MRI than those with larger heel spur, suggesting the size of plantar heel spur was not the major source of inflammation and pain in plantar fasciitis. On the other hand, a recent study found that patients with larger plantar heel spurs had significantly worse pain and function than those with smaller plantar heel spurs. ¹⁶ Wainwright et al ³² also reported that large plantar heel spurs can be more likely to be symptomatic in their case-control study. In our study, the size of plantar heel spur was significantly higher in the PF+S group than the C+S group. Furthermore, our multivariable regression analysis revealed that the size of plantar heel spur (>5.3 mm) was independently associated with PF+S condition. Although it is still hard to conclude if plantar heel spur is the reason for heel pain or the result from it, slightly increased average size of plantar heel spur was found associated with PF+S in this study.

Several radiographic studies reported a relationship between posterior heel spur and plantar heel spur.^30,34 Posterior heel spur has been postulated to occur from repetitive traction of the Achilles tendon at the insertion of the calcaneus, resulting in subsequent inflammation and spur formation. Zhu et al in their radiographic study demonstrated the relationship between posterior and plantar heel spurs in patients with insertional Achilles tendonitis. They explained this relationship by the increasing tension in the biomechanical complex involving the Achilles tendon, calcaneus, and plantar fascia. ³⁴ In contrast, other authors contend that plantar heel spurs are fundamentally different from posterior heel spurs in the Achilles tendon, citing anatomic investigations that report plantar heel spurs have vertically oriented trabecula rather than horizontally oriented trabecula.^15,18 They suggest that calcaneal spurs are fibrocartilaginous outgrowths formed in response to calcaneal stress fractures, which is to protect the calcaneus against microcracks. In our study, there was no significant difference in the incidence of posterior heel spur between the study and control groups and, further, posterior heel spur was not identified as an independent risk factor of painful heel.

This study has several limitations that must be mentioned. As this is a retrospective study, there is an inherent risk of bias. The groups are relatively small. The findings in this study may not be generalizable. The completeness and validity of the data relied on the content of the medical record. We admit that we could not include other possible risk factors of PF+S related to the mechanism of ankle joint, such as inappropriate foot position, weak foot and ankle strength, and Achilles tendon/gastrocnemius muscle tightness, because of the lack of enough data. Patients’ sport activity level was not evaluated, which could affect plantar heel pain. However, there were no elite or competitive athletics in our cohorts. Though we did not perform advanced imaging studies like MRI or ultrasonography, diagnosis of plantar fasciitis was based on clinical examination and patient history.

Conclusion

We found an association of both obesity and increased average plantar heel spur length on lateral radiographs in patients with painful plantar fasciitis when we compared those patients to a group of control patients with plantar heel spurs but no symptoms of plantar fasciitis. The presence of plantar heel spur alone did not account for the symptoms of plantar fasciitis.