551021
research-article2014
FAIXXX10.1177/1071100714551021Foot & Ankle InternationalSullivan et al
Article
Musculoskeletal and Activity-Related Factors Associated With Plantar Heel Pain
Foot & Ankle International® 2015, Vol. 36(1) 37–45 © The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1071100714551021 fai.sagepub.com
Justin Sullivan, PT, MHlthSc1, Joshua Burns, PhD2, Roger Adams, PhD1, Evangelos Pappas, PhD, PT1, and Jack Crosbie, PhD3
Abstract Background: Despite the prevalence and impact of plantar heel pain, its etiology remains poorly understood, and there is no consensus regarding optimum management. The identification of musculoskeletal factors related to the presence of plantar heel pain could lead to the development of better targeted intervention strategies and potentially improve clinical outcomes. The aim of this study was to investigate relationships between a number of musculoskeletal and activity-related measures and plantar heel pain. Methods: In total, 202 people with plantar heel pain and 70 asymptomatic control participants were compared on a variety of musculoskeletal and activity-related measures, including body mass index (BMI), foot and ankle muscle strength, calf endurance, ankle and first metatarsophalangeal (MTP) joint range of motion, foot alignment, occupational standing time, exercise level, and generalized hypermobility. Following a comparison of groups for parity of age, analyses of covariance were performed to detect differences between the 2 groups for any of the variables measured. Results: The plantar heel pain group displayed a higher BMI, reduced ankle dorsiflexion range of motion, reduced ankle evertor and toe flexor strength, and an altered inversion/eversion strength ratio. There were no differences between groups for foot alignment, dorsiflexor or invertor strength, ankle inversion or eversion range of motion, first MTP joint extension range of motion, generalized hypermobility, occupational standing time, or exercise level. Conclusion: Plantar heel pain is associated with higher BMI and reductions in some foot and ankle strength and flexibility measures. Although these factors could be either causal or consequential, they are all potentially modifiable and could be targeted in the management of plantar heel pain. Level of Evidence: Level III, comparative study. Keywords: Strength, flexibility, foot alignment, obesity Plantar heel pain is the most common foot disorder treated by health care practitioners32 and is estimated to affect approximately 10% of people at some stage of their life.10 In the United States, approximately 2 million people seek treatment for plantar heel pain every year39 at a cost of over $300 million.46 In addition to its prevalence, plantar heel pain has a negative impact on the quality of life of those who experience it, including limitations in performing physical tasks, reduced energy to participate in activities and social isolation.21 Despite its prevalence and impact, the etiology of plantar heel pain remains poorly understood,32 and there is no consensus regarding optimal intervention.9,29,40 Plantar heel pain is thought to occur due to excessive cumulative strain at the enthesis of the plantar fascia. Mechanical causes are thought to play a major role in the etiology of this condition, but corroborating evidence is limited.45,49 Plantar heel pain is considered to be multifactorial in nature, with many potential variables suggested as either risk factors or associated with the condition. These variables include foot alignment, ankle
and foot flexibility, muscle strength and endurance as well as body weight, the length of time spent standing, and activity levels in domestic and leisure pursuits. Currently, insufficient or conflicting evidence exists for the association between these factors and plantar heel pain.20,29,48 Recent guidelines report moderate evidence for limited ankle dorsiflexion range and high body mass index (BMI) being associated with plantar heel pain, but this conclusion was based on only 1 study involving 50 symptomatic participants.32 1
Discipline of Physiotherapy, Faculty of Health Sciences, The University of Sydney, Sydney, New South Wales, Australia 2 The Children’s Hospital at Westmead, The University of Sydney, Sydney, New South Wales, Australia 3 School of Science and Health, The University of Western Sydney, Sydney, New South Wales, Australia Corresponding Author: Justin Sullivan, PT, MHlthSc, Discipline of Physiotherapy, Faculty of Health Sciences, The University of Sydney, 75 East St, Lidcombe, NSW 2141, Australia. Email: [email protected]
Downloaded from fai.sagepub.com at SAINT JOSEPHS UNIV LIBRARY on February 13, 2015
38
Foot & Ankle International 36(1)
Uncertainty regarding the association between foot alignment and plantar heel pain is likely to be due to the small sample sizes used in studies to date,32 a common limitation across studies into plantar heel pain. In addition, minimal investigation of foot muscle strength or weight-bearing activity level has been undertaken. Therefore, a study with sufficient statistical power is needed to investigate the association between commonly used clinical measures and plantar heel pain. This study aimed to identify factors associated with plantar heel pain through comparison of musculoskeletal and activity-related variables in a large group of people with heel pain to asymptomatic controls. Differences found between the 2 groups could identify individual factors that are associated with the presence of plantar heel pain. A greater understanding of musculoskeletal and activityrelated factors associated with plantar heel pain could result in the development of better targeted management strategies and improved clinical outcomes.
Methods Participants In total, 202 people with plantar heel pain and 70 asymptomatic controls volunteered to participate in the study. People were recruited from the general public via local media advertisements, as well as notices in medical, physiotherapy, and university premises. Consistent with previous heel pain research28 and to ensure the establishment of the condition, symptomatic participants were required to have experienced plantar heel pain for at least 3 weeks. In accordance with current clinical guidelines,32 symptomatic participants were included if they reported tenderness on palpation of the medial calcaneal tuberosity and exhibited one of the following complaints: pain on the first step in the morning or after prolonged sitting, pain on prolonged standing,32,40 or pain when running.32 Asymptomatic participants were required to have no past or present history of plantar heel pain. Participants were excluded from either group if they had undergone surgery to the plantar fascia or had any of the following conditions: systemic arthritis, neurological conditions, lumbar radiculopathy, neurological or vascular compromise of the foot related to diabetes, or any coexisting painful musculoskeletal condition of the lower limb. Each participant attended data collection on a single occasion. In accordance with approval from the University of Sydney Human Research Ethics Committee, written consent was obtained, and all participants were screened for the presence of plantar heel pain.
Procedures Foot alignment. Foot alignment of each participant was measured using the Foot Posture Index (FPI).38 This tool
allows an individual foot to be scored along a scale ranging from more supinated to more pronated in the weight-bearing position. The FPI is a 25-point scale (from –12 to 12), using 5 observational measures and 1 palpation measure (each scored between –2 and 2) of the alignment of different segments of the foot and ankle (rearfoot, midfoot, forefoot). Zero is given to neutral alignment, negative scores are given to more supinated alignment, and positive scores given to more pronated alignment. Generalized hypermobility. The presence or absence of generalized joint hypermobility was ascertained using the Beighton Scale, a 9-point scale using 5 separate joint range-of-motion (ROM) measures (4 being performed bilaterally) across various regions of the body, with 1 point scored per joint exceeding normal ROM. A score of ≥4 is considered sufficient evidence of generalized hypermobility.23 Foot and ankle range of motion. The procedures for measuring first metatarsophalangeal (MTP) joint extension, ankle dorsiflexion, and rearfoot inversion and eversion are detailed in Table 1. Strength. Foot and ankle muscle strength was assessed using handheld dynamometry (JTech Commander PowerTrack II; JTech Medical, Salt Lake City, UT). High intratester and intertester reliability has been demonstrated using this approach in the assessment of ankle muscle strength.5,47 For each individual test, a make test was used with progressive muscle force being developed to achieve a maximum isometric contraction. Each test was performed 3 times, with the maximum result being selected for data analysis. The positioning for each individual test is described in Table 2. Calf endurance. As the absolute strength of the triceps surae muscle complex renders the use of handheld dynamometry ineffective, calf endurance was instead assessed using a standardized heel raise test, which has been shown to have high reliability.33 Participants stood at arm’s length from a wall with their feet underneath a wooden block positioned such that the top of their foot, or anterior ankle, touched the underside at full heel raise. This ensured that each time the participant performed the heel raise, he or she achieved full range of motion. The participants performed as many heel raises as they could until fatigue. Participants were asked to keep the knee straight, and a metronome was used to ensure each participant did the task at the same frequency. The number of heel raises was counted and recorded, with deductions made for any attempts that failed to reach the required height or for those involving knee flexion. Weight-bearing activity levels. Each participant’s occupational standing demands and weekly weight-bearing exercise levels were ascertained by a bespoke questionnaire. Participants who were employed in regular work were asked to
Downloaded from fai.sagepub.com at SAINT JOSEPHS UNIV LIBRARY on February 13, 2015
39
Sullivan et al Table 1. Foot and Ankle Range-of-Motion Measurement Procedures. Measure First MTP extension Ankle dorsiflexion
Ankle inversion and eversion
Positioning and Procedure Participants were in long sitting, with the ankle in plantargrade and the first metatarsal head in line with the heel when viewed from the medial side. The first MTP joint was extended maximally by the tester while preventing plantarflexion of the first ray. The angle formed by the lines connecting the navicular, the MTP joint axis, and the middle of the interphalangeal joint was measured with a goniometer. Ankle dorsiflexion range was measured using both the flexed knee lunge test3 and the straight knee lunge test.34 For the flexed knee lunge test, participants stood with their hands resting against a wall, with the foot being tested one step behind the other. They flexed their back knee directly over the foot until the heel began to leave the ground. The range of motion was measured with a digital inclinometer (Chattanooga Baseline; DJO Global, Vista, CA, USA) placed on the lowest part of the tibia anteriorly. For the straight knee lunge test, the same procedure was used except that the knee on the side of the foot being tested was kept straight. For measuring eversion, participants were positioned on the side being tested and the ankle in neutral plantarflexion/dorsiflexion. The rearfoot was then placed into maximum eversion by the examiner. A digital inclinometer was placed along the medial tibial border, just proximal to the medial malleolus, and zeroed (Figure 1A). Eversion was measured by placing the inclinometer flat along the medial calcaneal border, just posterior to the medial calcaneal tuberosity (Figure 1B). Ankle inversion was measured with a similar procedure, but the tester positioned the ankle in maximum inversion prior to zeroing the inclinometer.
MTP, metatarsophalangeal.
estimate the length of time they would spend standing during a normal day’s work, and this was recorded in hours. They were also asked to detail their regular exercise habits, including type of exercise, frequency per week, and duration of sessions. Non–weight-bearing exercise, such as swimming, was not included as minimal loading to the plantar foot occurs during such tasks. The total length of time spent per week doing weight-bearing exercise was also recorded in hours. Symptomatic participants were asked to detail their occupational standing time and exercise participation based on the time they first started experiencing heel pain, as this would be more representative of the loads occurring at the heel at the time that the condition was developing.
Statistical Analyses
Figure 1. (A) Eversion measurement: zero position. (B) Eversion measurement: calcaneal angle.
Statistical analyses were carried out using SPSS, version 19 (SPSS, Inc, an IBM Company, Chicago, IL). The 2 groups were compared for age and sex prior to further analyses, because these variables could possibly influence strength and flexibility measures within each group. Age and sex were compared using an independent groups t test with the level of significance set at α = 0.05. Following this, analyses of covariance were carried out to compare each variable between the symptomatic and asymptomatic groups with the level of significance at α = 0.05. Partial η2 values were calculated to report an effect size for each variable found to differ between the 2 groups. Values greater than 0.01 were considered representative of a small difference, values greater than 0.06 representative of a medium-sized effect, and values greater than 0.14 representative of a large difference between groups.8
Downloaded from fai.sagepub.com at SAINT JOSEPHS UNIV LIBRARY on February 13, 2015
40
Foot & Ankle International 36(1)
Table 2. Foot and Ankle Strength Measurement Procedures. Measure Foot and ankle strength Toe flexor strength
Procedure Preparation Participants sat with their hips in 90 degrees of flexion, knees extended, and feet over the end of the examination table. A rolled towel or pillow was placed under the knees to reduce neural or hamstring-related tension. Participants were instructed to hold the edge of the treatment table for extra stability. The ankle was then placed in neutral plantarflexion/dorsiflexion by the examiner. For dorsiflexion strength, the handheld dynamometer was placed on the dorsum of the foot, just proximal to the metatarsal heads. For inversion strength, the handheld dynamometer was placed on the medial side of the foot, just proximal to the first metatarsal head. For eversion strength, handheld dynamometer was placed on the lateral side of the foot, just proximal to the fifth metatarsal head. The inversion/eversion strength ratio was calculated by dividing the inversion strength score by the eversion strength score. Participants sat with their knees and hips at approximately 90 degrees, with their feet on a wooden block. The toes of the foot being tested were positioned clear of the edge of the block, with the MTP and interphalangeal joints positioned in neutral. For great toe flexor strength, the head of the handheld dynamometer was placed longitudinally along the length of the plantar aspect of the great toe (Figure 2A). For lesser toe flexor strength, the dynamometer was placed across the plantar surface of the second, third, and fourth toes (Figure 2B).
MTP, metatarsophalangeal.
Figure 2. (A) Great toe strength measurement. (B) Lesser toe strength measurement.
With 202 participants with heel pain and 70 in the control group, the harmonic mean group size was 103. This results in a power of 0.8 for detecting differences between groups as large as 0.4 standard deviation units on each measure. This study, therefore, had good power to detect smallto medium-size differences between the asymptomatic and symptomatic groups as significant.7
Results The characteristics of the participants in each group are summarized in Table 3. Since age was found to differ significantly between the 2 groups, analyses of covariance (ANCOVAs) were carried out using age as the covariate to control its effect on the musculoskeletal and activity-related variables. Results of these analyses are summarized in Table 4.
Compared with the control group, members of the plantar heel pain group had a higher BMI, reduced eversion strength, higher inversion/eversion strength ratio, and reduced strength in both the great toe and lesser toe flexors. There were no differences between groups for the FPI, generalized hypermobility, first MTP joint extension range of motion, ankle inversion or eversion range of motion, dorsiflexion or inversion strength, calf endurance, occupational standing time, or exercise time.
Discussion This study has the largest sample of symptomatic participants used to investigate the association between plantar heel pain and commonly measured musculoskeletal and activityrelated factors. The findings of this study support previously reported, moderate-level evidence for high BMI and reduced
Downloaded from fai.sagepub.com at SAINT JOSEPHS UNIV LIBRARY on February 13, 2015
41
Sullivan et al Table 3. Participant Characteristics. Characteristic
Heel Pain Group (n = 202)
Age, y Sex, female, No. (%) Height, m Weight, kg Pain duration, median (IQR), mo
55 (13.5) 134 (66) 1.67 (0.087) 79.7 (16.3) 10.0 (4.0-24.0)
Control Group (n = 70)
P Value
48 (17.1) 42 (60) 1.67 (0.097) 71.8 (14.1) NA
.002 .340 .521
research-article2014
FAIXXX10.1177/1071100714551021Foot & Ankle InternationalSullivan et al
Article
Musculoskeletal and Activity-Related Factors Associated With Plantar Heel Pain
Foot & Ankle International® 2015, Vol. 36(1) 37–45 © The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1071100714551021 fai.sagepub.com
Justin Sullivan, PT, MHlthSc1, Joshua Burns, PhD2, Roger Adams, PhD1, Evangelos Pappas, PhD, PT1, and Jack Crosbie, PhD3
Abstract Background: Despite the prevalence and impact of plantar heel pain, its etiology remains poorly understood, and there is no consensus regarding optimum management. The identification of musculoskeletal factors related to the presence of plantar heel pain could lead to the development of better targeted intervention strategies and potentially improve clinical outcomes. The aim of this study was to investigate relationships between a number of musculoskeletal and activity-related measures and plantar heel pain. Methods: In total, 202 people with plantar heel pain and 70 asymptomatic control participants were compared on a variety of musculoskeletal and activity-related measures, including body mass index (BMI), foot and ankle muscle strength, calf endurance, ankle and first metatarsophalangeal (MTP) joint range of motion, foot alignment, occupational standing time, exercise level, and generalized hypermobility. Following a comparison of groups for parity of age, analyses of covariance were performed to detect differences between the 2 groups for any of the variables measured. Results: The plantar heel pain group displayed a higher BMI, reduced ankle dorsiflexion range of motion, reduced ankle evertor and toe flexor strength, and an altered inversion/eversion strength ratio. There were no differences between groups for foot alignment, dorsiflexor or invertor strength, ankle inversion or eversion range of motion, first MTP joint extension range of motion, generalized hypermobility, occupational standing time, or exercise level. Conclusion: Plantar heel pain is associated with higher BMI and reductions in some foot and ankle strength and flexibility measures. Although these factors could be either causal or consequential, they are all potentially modifiable and could be targeted in the management of plantar heel pain. Level of Evidence: Level III, comparative study. Keywords: Strength, flexibility, foot alignment, obesity Plantar heel pain is the most common foot disorder treated by health care practitioners32 and is estimated to affect approximately 10% of people at some stage of their life.10 In the United States, approximately 2 million people seek treatment for plantar heel pain every year39 at a cost of over $300 million.46 In addition to its prevalence, plantar heel pain has a negative impact on the quality of life of those who experience it, including limitations in performing physical tasks, reduced energy to participate in activities and social isolation.21 Despite its prevalence and impact, the etiology of plantar heel pain remains poorly understood,32 and there is no consensus regarding optimal intervention.9,29,40 Plantar heel pain is thought to occur due to excessive cumulative strain at the enthesis of the plantar fascia. Mechanical causes are thought to play a major role in the etiology of this condition, but corroborating evidence is limited.45,49 Plantar heel pain is considered to be multifactorial in nature, with many potential variables suggested as either risk factors or associated with the condition. These variables include foot alignment, ankle
and foot flexibility, muscle strength and endurance as well as body weight, the length of time spent standing, and activity levels in domestic and leisure pursuits. Currently, insufficient or conflicting evidence exists for the association between these factors and plantar heel pain.20,29,48 Recent guidelines report moderate evidence for limited ankle dorsiflexion range and high body mass index (BMI) being associated with plantar heel pain, but this conclusion was based on only 1 study involving 50 symptomatic participants.32 1
Discipline of Physiotherapy, Faculty of Health Sciences, The University of Sydney, Sydney, New South Wales, Australia 2 The Children’s Hospital at Westmead, The University of Sydney, Sydney, New South Wales, Australia 3 School of Science and Health, The University of Western Sydney, Sydney, New South Wales, Australia Corresponding Author: Justin Sullivan, PT, MHlthSc, Discipline of Physiotherapy, Faculty of Health Sciences, The University of Sydney, 75 East St, Lidcombe, NSW 2141, Australia. Email: [email protected]
Downloaded from fai.sagepub.com at SAINT JOSEPHS UNIV LIBRARY on February 13, 2015
38
Foot & Ankle International 36(1)
Uncertainty regarding the association between foot alignment and plantar heel pain is likely to be due to the small sample sizes used in studies to date,32 a common limitation across studies into plantar heel pain. In addition, minimal investigation of foot muscle strength or weight-bearing activity level has been undertaken. Therefore, a study with sufficient statistical power is needed to investigate the association between commonly used clinical measures and plantar heel pain. This study aimed to identify factors associated with plantar heel pain through comparison of musculoskeletal and activity-related variables in a large group of people with heel pain to asymptomatic controls. Differences found between the 2 groups could identify individual factors that are associated with the presence of plantar heel pain. A greater understanding of musculoskeletal and activityrelated factors associated with plantar heel pain could result in the development of better targeted management strategies and improved clinical outcomes.
Methods Participants In total, 202 people with plantar heel pain and 70 asymptomatic controls volunteered to participate in the study. People were recruited from the general public via local media advertisements, as well as notices in medical, physiotherapy, and university premises. Consistent with previous heel pain research28 and to ensure the establishment of the condition, symptomatic participants were required to have experienced plantar heel pain for at least 3 weeks. In accordance with current clinical guidelines,32 symptomatic participants were included if they reported tenderness on palpation of the medial calcaneal tuberosity and exhibited one of the following complaints: pain on the first step in the morning or after prolonged sitting, pain on prolonged standing,32,40 or pain when running.32 Asymptomatic participants were required to have no past or present history of plantar heel pain. Participants were excluded from either group if they had undergone surgery to the plantar fascia or had any of the following conditions: systemic arthritis, neurological conditions, lumbar radiculopathy, neurological or vascular compromise of the foot related to diabetes, or any coexisting painful musculoskeletal condition of the lower limb. Each participant attended data collection on a single occasion. In accordance with approval from the University of Sydney Human Research Ethics Committee, written consent was obtained, and all participants were screened for the presence of plantar heel pain.
Procedures Foot alignment. Foot alignment of each participant was measured using the Foot Posture Index (FPI).38 This tool
allows an individual foot to be scored along a scale ranging from more supinated to more pronated in the weight-bearing position. The FPI is a 25-point scale (from –12 to 12), using 5 observational measures and 1 palpation measure (each scored between –2 and 2) of the alignment of different segments of the foot and ankle (rearfoot, midfoot, forefoot). Zero is given to neutral alignment, negative scores are given to more supinated alignment, and positive scores given to more pronated alignment. Generalized hypermobility. The presence or absence of generalized joint hypermobility was ascertained using the Beighton Scale, a 9-point scale using 5 separate joint range-of-motion (ROM) measures (4 being performed bilaterally) across various regions of the body, with 1 point scored per joint exceeding normal ROM. A score of ≥4 is considered sufficient evidence of generalized hypermobility.23 Foot and ankle range of motion. The procedures for measuring first metatarsophalangeal (MTP) joint extension, ankle dorsiflexion, and rearfoot inversion and eversion are detailed in Table 1. Strength. Foot and ankle muscle strength was assessed using handheld dynamometry (JTech Commander PowerTrack II; JTech Medical, Salt Lake City, UT). High intratester and intertester reliability has been demonstrated using this approach in the assessment of ankle muscle strength.5,47 For each individual test, a make test was used with progressive muscle force being developed to achieve a maximum isometric contraction. Each test was performed 3 times, with the maximum result being selected for data analysis. The positioning for each individual test is described in Table 2. Calf endurance. As the absolute strength of the triceps surae muscle complex renders the use of handheld dynamometry ineffective, calf endurance was instead assessed using a standardized heel raise test, which has been shown to have high reliability.33 Participants stood at arm’s length from a wall with their feet underneath a wooden block positioned such that the top of their foot, or anterior ankle, touched the underside at full heel raise. This ensured that each time the participant performed the heel raise, he or she achieved full range of motion. The participants performed as many heel raises as they could until fatigue. Participants were asked to keep the knee straight, and a metronome was used to ensure each participant did the task at the same frequency. The number of heel raises was counted and recorded, with deductions made for any attempts that failed to reach the required height or for those involving knee flexion. Weight-bearing activity levels. Each participant’s occupational standing demands and weekly weight-bearing exercise levels were ascertained by a bespoke questionnaire. Participants who were employed in regular work were asked to
Downloaded from fai.sagepub.com at SAINT JOSEPHS UNIV LIBRARY on February 13, 2015
39
Sullivan et al Table 1. Foot and Ankle Range-of-Motion Measurement Procedures. Measure First MTP extension Ankle dorsiflexion
Ankle inversion and eversion
Positioning and Procedure Participants were in long sitting, with the ankle in plantargrade and the first metatarsal head in line with the heel when viewed from the medial side. The first MTP joint was extended maximally by the tester while preventing plantarflexion of the first ray. The angle formed by the lines connecting the navicular, the MTP joint axis, and the middle of the interphalangeal joint was measured with a goniometer. Ankle dorsiflexion range was measured using both the flexed knee lunge test3 and the straight knee lunge test.34 For the flexed knee lunge test, participants stood with their hands resting against a wall, with the foot being tested one step behind the other. They flexed their back knee directly over the foot until the heel began to leave the ground. The range of motion was measured with a digital inclinometer (Chattanooga Baseline; DJO Global, Vista, CA, USA) placed on the lowest part of the tibia anteriorly. For the straight knee lunge test, the same procedure was used except that the knee on the side of the foot being tested was kept straight. For measuring eversion, participants were positioned on the side being tested and the ankle in neutral plantarflexion/dorsiflexion. The rearfoot was then placed into maximum eversion by the examiner. A digital inclinometer was placed along the medial tibial border, just proximal to the medial malleolus, and zeroed (Figure 1A). Eversion was measured by placing the inclinometer flat along the medial calcaneal border, just posterior to the medial calcaneal tuberosity (Figure 1B). Ankle inversion was measured with a similar procedure, but the tester positioned the ankle in maximum inversion prior to zeroing the inclinometer.
MTP, metatarsophalangeal.
estimate the length of time they would spend standing during a normal day’s work, and this was recorded in hours. They were also asked to detail their regular exercise habits, including type of exercise, frequency per week, and duration of sessions. Non–weight-bearing exercise, such as swimming, was not included as minimal loading to the plantar foot occurs during such tasks. The total length of time spent per week doing weight-bearing exercise was also recorded in hours. Symptomatic participants were asked to detail their occupational standing time and exercise participation based on the time they first started experiencing heel pain, as this would be more representative of the loads occurring at the heel at the time that the condition was developing.
Statistical Analyses
Figure 1. (A) Eversion measurement: zero position. (B) Eversion measurement: calcaneal angle.
Statistical analyses were carried out using SPSS, version 19 (SPSS, Inc, an IBM Company, Chicago, IL). The 2 groups were compared for age and sex prior to further analyses, because these variables could possibly influence strength and flexibility measures within each group. Age and sex were compared using an independent groups t test with the level of significance set at α = 0.05. Following this, analyses of covariance were carried out to compare each variable between the symptomatic and asymptomatic groups with the level of significance at α = 0.05. Partial η2 values were calculated to report an effect size for each variable found to differ between the 2 groups. Values greater than 0.01 were considered representative of a small difference, values greater than 0.06 representative of a medium-sized effect, and values greater than 0.14 representative of a large difference between groups.8
Downloaded from fai.sagepub.com at SAINT JOSEPHS UNIV LIBRARY on February 13, 2015
40
Foot & Ankle International 36(1)
Table 2. Foot and Ankle Strength Measurement Procedures. Measure Foot and ankle strength Toe flexor strength
Procedure Preparation Participants sat with their hips in 90 degrees of flexion, knees extended, and feet over the end of the examination table. A rolled towel or pillow was placed under the knees to reduce neural or hamstring-related tension. Participants were instructed to hold the edge of the treatment table for extra stability. The ankle was then placed in neutral plantarflexion/dorsiflexion by the examiner. For dorsiflexion strength, the handheld dynamometer was placed on the dorsum of the foot, just proximal to the metatarsal heads. For inversion strength, the handheld dynamometer was placed on the medial side of the foot, just proximal to the first metatarsal head. For eversion strength, handheld dynamometer was placed on the lateral side of the foot, just proximal to the fifth metatarsal head. The inversion/eversion strength ratio was calculated by dividing the inversion strength score by the eversion strength score. Participants sat with their knees and hips at approximately 90 degrees, with their feet on a wooden block. The toes of the foot being tested were positioned clear of the edge of the block, with the MTP and interphalangeal joints positioned in neutral. For great toe flexor strength, the head of the handheld dynamometer was placed longitudinally along the length of the plantar aspect of the great toe (Figure 2A). For lesser toe flexor strength, the dynamometer was placed across the plantar surface of the second, third, and fourth toes (Figure 2B).
MTP, metatarsophalangeal.
Figure 2. (A) Great toe strength measurement. (B) Lesser toe strength measurement.
With 202 participants with heel pain and 70 in the control group, the harmonic mean group size was 103. This results in a power of 0.8 for detecting differences between groups as large as 0.4 standard deviation units on each measure. This study, therefore, had good power to detect smallto medium-size differences between the asymptomatic and symptomatic groups as significant.7
Results The characteristics of the participants in each group are summarized in Table 3. Since age was found to differ significantly between the 2 groups, analyses of covariance (ANCOVAs) were carried out using age as the covariate to control its effect on the musculoskeletal and activity-related variables. Results of these analyses are summarized in Table 4.
Compared with the control group, members of the plantar heel pain group had a higher BMI, reduced eversion strength, higher inversion/eversion strength ratio, and reduced strength in both the great toe and lesser toe flexors. There were no differences between groups for the FPI, generalized hypermobility, first MTP joint extension range of motion, ankle inversion or eversion range of motion, dorsiflexion or inversion strength, calf endurance, occupational standing time, or exercise time.
Discussion This study has the largest sample of symptomatic participants used to investigate the association between plantar heel pain and commonly measured musculoskeletal and activityrelated factors. The findings of this study support previously reported, moderate-level evidence for high BMI and reduced
Downloaded from fai.sagepub.com at SAINT JOSEPHS UNIV LIBRARY on February 13, 2015
41
Sullivan et al Table 3. Participant Characteristics. Characteristic
Heel Pain Group (n = 202)
Age, y Sex, female, No. (%) Height, m Weight, kg Pain duration, median (IQR), mo
55 (13.5) 134 (66) 1.67 (0.087) 79.7 (16.3) 10.0 (4.0-24.0)
Control Group (n = 70)
P Value
48 (17.1) 42 (60) 1.67 (0.097) 71.8 (14.1) NA
.002 .340 .521
