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Risk factors associated with the development of plantar heel pain in athletes
Original Article
Risk factors associated with the development of plantar heel pain in athletes Keith Rome, Tracey Howe and Ian Haslock
Keith Rome PhD, MSc, BSc(Hons) DPodM, SRch, Rehabilitation Research Unit, Postgraduate Institute for Health and Social Care, School of Health, University of Teesside, Middlesbrough, UK TS1 3BA. E-mail: [email protected]. uk; Tel.: 44 (0) 16 42 384977; Fax: 44 (0) 1642 384105 Tracey Howe PhD, MSc, GradDipPhys, Director of Postgraduate Institute for Health and Social Care, Rehabilitation Research Unit, School of Health, Physiotherapy, University of Teesside Ian Haslock FRCP, MD, Rheumatology Department, South Cleveland Hospital, Middlesbrough, UK
The aetiology of plantar heel pain-running injuries is controversial, with conflicting evidence pertaining to its development. A cross-sectional design was used to calculate prevalence rates and the association of risk factors with plantar heel pain (PHP). One hundred and sixty-six subjects (mean age 23.9, SD 7.1 years) were assessed. A prevalence rate of 21.7% was determined. Independent t-tests and w2 analysis evaluated the association between the risk factors and PHP at the 5% level. The results demonstrated that young age and previous injury were significantly associated with PHP (P < 0.05), and all other risk factors were non-significant (P < 0.05). The results demonstrated that traditional risk factors such as excessive foot pronation, ankle equinus, and body weight are not associated with PHP. Recommendations include regular clinical evaluation of athletes with a history of PHP to prevent reoccurrence. ß 2001 Harcourt Publishers Ltd
Introduction Plantar heel pain (PHP) in runners has been described as an overuse injury associated with the accumulation of repetitive force over time rather than a single traumatic event (Krivickas 1997). The heterogeneity of disorders grouped together as plantar heel pain makes it dif®cult to unravel its de®nitive aetiology, and there appears to be a variety of controversial theories as to the actual cause of PHP (Ali et al. 1995). Many factors that may possibly in¯uence risk of injury have been previously been identi®ed (Neely 1998). These factors are commonly referred to as risk factors and have been classi®ed as intrinsic or extrinsic (Caine et al. 1996). Intrinsic risk factors are individual anatomical and biological characteristics predisposing a person to the outcome of injury, while extrinsic risk factors have an effect on the sport participant `from without' (Table 1). Meeuwisse (1994) proposed that intrinsic factors are factors which predispose the runner to
119 The Foot (2001) 11, 119±125
doi: 10.1054/foot.2001.0698, available online at http://www.idealibrary.com on
react in a speci®c manner to an injury situation. However, once the runner is predisposed, extrinsic factors such as previous injuries may facilitate manifestation of injury, and may interact to make the runner more susceptible to injury. Although risk factors may render the runner more susceptible to injury, they are usually not suf®cient in themselves for an injury to occur. The ®nal element in the web of causation involves an inciting event and injury mechanism. An inciting event may be viewed as a precipitant factor associated with the de®nitive onset of injury, such as running on a slippery surface (Meeuwisse 1994). One of the most widely stated anatomical risk factor associated with PHP is excessive foot pronation (Warren 1984, James et al. 1978, Warren & Jessie-Jones 1987). Limited ankle joint dorsi¯exion range of motion has also been reported to be associated with PHP (Amis et al. 1988, Kibler et al. 1991, Hill 1996). PHP has been reported in subjects 7±85 years old in both the recreational and population-based studies
ß 2001 Harcourt Publishers Ltd
Development of plantar heel pain in athletes
Table 1 Intrinsic and extrinsic risk factors associated with plantar heel pain Extrinsic risk factors
Intrinsic risk factors
Running surface
Biological: age, gender, weight, height
Speed and frequency of running
Anatomical: range of motion at ankle and subtalar joints
Miles run per week Previous injury
(Taunton et al. 1982, Kibler et al. 1991, James et al. 1978). The effect of high or low weight has been examined from several perspectives. In the athletic literature, one study demonstrated no clear evidence of BMI on injury rates (Neely 1998), while other studies have reported a U-shaped relationship such that both the lightest and the heaviest group of runners were at increased risk for injuries (Marti 1988). Previous studies on extrinsic risk factors associated with PHP are limited, although there have been tentative links with the development of PHP with previous injury, running surfaces and past experience (Warren 1984, 1987). A review of the literature suggests that the relationship between intrinsic and extrinsic risk factors associated with PHP is unclear. The aim of the study was to determine the prevalence rate of PHP and to evaluate intrinsic and extrinsic risk factors associated with PHP in a cohort of runners.
Methods To calculate the sample size, a 90% power calculation was performed based upon pilot work on vertical navicular height measurements. The prevalence rate of PHP in the sporting population has been reported to be 8±21% (Rome 1997). Therefore, to achieve a 21% prevalence rate, a sample size of 166 subjects was required. One hundred and thirty subjects were designated into a non-PHP group and 36 subjects diagnosed with PHP. The subjects were conveniently sampled from local athletic clubs and the University sports clubs. All subjects were free to withdraw from the study at any time and informed consent forms were completed prior to entry. The University Ethics Committee approved this study. In the current study, the subjects were de®ned as any sportsperson running regularly as part of
120 The Foot (2001) 11, 119±125
their main physical activity. PHP was de®ned as pain unilateral in nature with at least 2 months' duration that is attributed to physical activity. The subject described either a history of night-time or early morning plantar heel pain, which decreased after walking, and/or increased after exercise or prolonged periods of standing (Wall et al. 1993). The problem had to be severe enough to either cause a reduction in physical activity, a visit to a health professional, or the use of medication. The subject had to be in good general health, with no known history of systemic disease, including rheumatoid arthritis, seronegative arthritis or gout. Exclusion criteria included previous foot surgery, recent abrupt trauma to the foot, congenital defects of the lower extremity, or corticosteroid injection in the heel in the previous 3 months (Wall et al. 1993).
Measurement of foot pronation Foot pronation was measured by using the height of the navicular from a static weight-bearing position. Vertical navicular height is frequently used as a measure of pronation (Vicenzino et al. 2000). To calculate the navicular height, the most prominent palpable portion of the navicular tuberosity was marked with a dot using a ®ne-black felt-tip pen when the subject was prone. The subject stood on a raised platform and was placed in a bilateral weight-bearing stance position. A modi®ed digital caliper (Mitutoyo Ltd, Andover, UK) was used to measure navicular height. The caliper was set to zero prior to measurements, and placed vertically on the inner side of the foot just anterior to the navicular. The distance (in millimetres) from the ®xed end of the caliper to the mark on the navicular tuberosity was measured. An intraclass correlation (ICC) was undertaken to evaluate the reliability of the technique using 20 healthy subjects over two occasions and the results demonstrated good reliability (ICC 0.85). Previous studies have reported similar ®ndings (Ator et al. 1991, Vicenzino et al. 1997).
Measurement of ankle joint dorsiflexion Each subject was in a reclined and fully supported supine position on a padded examination couch with the hip and knee joints fully extended and the lower legs extended over the edge of the couch by
ß 2001 Harcourt Publishers Ltd
Development of plantar heel pain in athletes
about 15±18 cm (Thoms & Rome 1997). The ankle joint was measured from a zero starting position. In this case, the subtalar neutral position was chosen as it is the most commonly recommended within clinical practice (Rome 1996). The method used to obtain this neutral position was by palpation of the congruency of the talar head (McPoil & Brocato 1990). From the zero position, the subject dorsi¯exed the ankle as far as possible, and was then asked to maintain this position until the ®rst measurement was obtained. Three measurements were taken and the mean (SD) were calculated for each set of three measurements.
Measurement of biological factors Body mass index (BMI) was calculated using the equation weight/height2, a method commonly used to evaluate an increase or decrease in body weight. Height and weight were also examined independently using calibrated instrumentation. Age was strati®ed into adolescents (14±19 years old) and adults ( $ 20 years old). Pilot work demonstrated that stratifying subjects into 10-year age bands (10±19; 20±29; 30±39; 40±49; > 50 years old) proved to be dif®cult, because the subject groups were too small for analysis. Collapsing cells into the two categorical groups allowed appropriate w2 analysis.
Data analysis Data were analyzed using SPSS for Windows and involved independent t-tests or w2 analysis of each risk factor to evaluate any signi®cant differences between PHP and non-PHP groups, at the 5% level. Ankle joint dorsi¯exion measurements were further strati®ed into subjects with less than 108 of dorsi¯exion from a zero position (ankle equinus) and those above 108 of ankle joint dorsi¯exion as is commonly indicated in clinical practice (Root et al. 1971).
Results Thirty-six subjects were diagnosed with PHP, producing a prevalence rate of 21.7%. Baseline characteristics demonstrated that PHP subjects ran for an average of 13.1 miles week, while non-PHP subjects ran for an average of 12.1 miles per week (Table 2). Signi®cant differences were demonstrated between previous injuries (P 0.001) and PHP. All other factors associated with a running history were non-signi®cant. Twenty-nine per cent (29%) of those subjects with PHP reported pain when standing for long periods, with 15% reporting PHP increasing in the cold weather. Fifty-three per cent (53%) of subjects reported PHP when standing on tiptoe or experiencing pain in the ®rst 50±100 steps. Approximately one-quarter (24%) of those subjects
Sporting history Baseline characteristics of the cohort were collated using a self-administered questionnaire at the time of baseline data collection. This method of collection ensures a high response rate, accurate sampling and a minimum of interviewer bias, while permitting interviewer assessments, providing necessary explanations and giving the bene®t of a degree of personal contact. Pilot work involving content and face validity were used to construct the questionnaire. The topic areas were constructed from previous literature, physical ®ndings, and clinical observation relating to lower limb sports injuries. Speci®c questions relating to PHP running history, which included running speed, previous injury, running experience, and miles run per week, were constructed from previous studies (Warren 1984, Warren & Jessie-Jones 1987, Wall et al. 1993, Weil et al. 1994).
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Table 2 Baseline characteristics of study participants P-value Years running
0.60
Reasons for running
0.66
Type of training
0.44
Previous injuries
0.01
Type of running surface Hill terrain
0.68
Concrete
0.17
Asphalt
0.39
Grass
0.92
Astroturf or other synthetic surface
0.76
Cambered
0.45
Miles run per week
0.25
Speed (miles/min)
0.28
Significant at the 5% level.
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Development of plantar heel pain in athletes
Table 3 Means (standard deviations) and statistical analysis of independent variables in the two plantar heel pain groups Independent variables
PHP group (n 36) Mean (SD)
Non-PHP group (n 130) Mean (SD)
P-value
Age (years)
24.6 (7.7)
21.7 (5.1)
0.01*
Ankle dorsiflexion (8)
16.0 (5.8)
15.9 (6.3)
0.39
Ankle equinus (<108)
7.7 (1.9)
7.2 (1.6)
0.30
32.7 (7.0)
31.5 (7.3)
0.37
23.14 (3.3)
23.23 (2.8)
0.91
1.73 (0.1)
1.75 (0.1)
0.31
69.45 (12.1)
71.53 (12.4)
0.31
Navicular height (mm) 2
BMI (weight /metre ) Height (m) Weight (Kg) At 5% significant level.
with PHP reported a reduction in weekly physical activity, with 16% reported visiting a health professional and only 9% took medication for PHP. Only 13% of subjects reported to have been given a medical diagnosis. No subjects reported having steroid injections for heel pain in the last 12 months. The results demonstrated no signi®cant differences (P 0.39) in ankle joint dorsi¯exion between PHP and non-PHP groups (Table 3). Even adjusting for ankle equinus, there was no signi®cant difference between PHP and non-PHP groups (P 0.78). There was no signi®cant difference in excessive foot pronation between PHP and non-PHP groups using the navicular height technique (P 0.37) or accounting for foot length (P 0.34). The results also found no signi®cant difference in height (P 0.31), weight (P 0.93), and BMI (P 0.56) between the PHP and non-PHP groups.
Discussion The results from the current study suggest that foot pronation is not associated with PHP in runners. Other epidemiological studies have found similar evidence (Kaufman et al. 1999, Hunt et al. 2000). It has been suggested from the literature that a combination of foot pronation and substantial movement transfer of the foot into internal tibial rotation is a better predictor of the development of overuse injuries (Hintermann et al. 1994). The excessive foot pronation may therefore have a secondary effect on the lower extremities, such as an increased compensatory internal rotation of the tibia which may predispose individuals to overloading stress on the medial aspect of
122 The Foot (2001) 11, 119±125
the foot and cause PHP. Increased rotation of the tibia may also give more proximal effects through the femur and the pelvis. However, recent work have suggested that the relationship between foot pronation, lower extremity kinematics ± in particular increased rotation of the tibia ± and clinical symptoms must be viewed with caution and evaluated on a patient-by-patient basis rather than with reference to the sporting or general population (Reischl et al. 1999). The results from the current study demonstrated that ankle joint dorsi¯exion was not associated with PHP. Further analysis using the standard 108 as a reference point demonstrated no signi®cant differences (P 0.96) between the PHP and non-PHP groups, suggesting that limited ankle joint dorsi¯exion is not associated with the development of PHP. Common clinical practice states that a minimum of 108 of ankle joint dorsi¯exion is necessary for normal locomotion. If subjects have less than this minimum requirement, then this could lead to functional ankle equinus (Root et al. 1971). Although the current study found no signi®cant difference between the PHP groups using the criterion of less than 108 dorsi¯exion, subjects may have been able to compensate for insuf®cient ankle dorsi¯exion in a variety of ways. Some subjects may compensate by decreasing step length, while others have a symmetrical and normal step length but have hypermobile dorsi¯exion of the forefoot on the rearfoot. Another compensation is an increase in the toe-out foot placement angle, so that ankle dorsi¯exion demands during late stance phase of the gait cycle are decreased (Hill 1996).
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Development of plantar heel pain in athletes
Alterations in BMI have been implicated as risk factors in the development of PHP. Subjects with high BMI may have excessive biomechanical and physiological stresses on their musculoskeletal system because of the extra weight. Those subjects with a low BMI may not have enough lean body mass to support their weight during the stresses of vigorous physical activity. However, the current study demonstrated that BMI was not signi®cantly associated with PHP, suggesting that BMI is therefore not a risk factor associated with PHP in runners. The results demonstrated that age was signi®cantly associated with PHP, which was somewhat surprising. The majority of young adults either attended University or local athletic clubs and participated in weekly and daily athletic training. One can postulate that younger runners may indeed to be more prone to the development of PHP than older runners. Younger runners possibly train at higher speeds and run more miles per week than older runners. The lower prevalence in adult respondents, who were relatively fewer in numbers, may represent a survival phenomenon where, if a runner is still running at an older age, it is because they have survived the injuries that cause many runners to leave the sport. Previous PHP running studies (Taunton et al. 1982, Warren 1984) have implicated excessive mileage as a cause of PHP in runners, although the results from the current study demonstrated no statistically signi®cant difference in overall mean distance per week between PHP group and non-PHP group. Furthermore, 48% of PHP subjects were running for less than 20 miles per week, and only 2% of the PHP subjects were running more than 80 miles per week. This ®nding is supported by several studies which suggest that total weekly mileage alone cannot explain injury patterns (James et al. 1978, Messier & Pittala 1988). The runners with PHP in this study ran on average 2.2 times per week for 13.1 miles per week at a speed less than 8 min/mile. Non-PHP subjects ran on average 1.9 times per week for 12.1 miles at a speed less than 8 min/mile. If compared with the populations of other studies (Walter et al. 1989, Macera 1992), the average subject in the current study can be considered as representing the recreational runner who runs for pleasure and health rather than for competition, and who participates in other physical activity.
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The variable ®tness levels or experience of the subjects may confound the inconclusive information about the in¯uence of exposure on PHP rates in physical activity. Previous studies have suggested that runners who have been running for less than three years or who are generally inexperienced may be at a greater risk of injury (Marti 1988, Macera 1992). However, the data from the current study suggest that running experience is not a risk factor for developing PHP. The present study encompassed a wide range of ability, from elite, nationally ranked runners to casual, ®rst- time runners. Subjects used in previous PHP studies have been limited to very speci®c populations either participating in marathons or road races, or have consisted of habitual runners. This limits the application of results to a speci®c type of runner across a larger population. To the authors' knowledge, this paper describes the ®rst study to examine runners who run but who do not compete in marathons or road races. Likewise, previous studies which conducted case series designs only evaluated runners who went to seek medical advice from a health professional or sports injury clinic and did not consider runners who were injured and did not seek treatment (Taunton et al. 1982, Warren 1984). Consequently, PHP running studies are negatively affected by sampling and non-random selection of subjects. Physical activity mostly takes place in an outdoor environment and is subject to a great deal of in¯uence by weather, running surfaces, and running terrain. Running injury has been attributed to a change in running surface, in particular hill-running, which has been commonly quoted as a risk factor associated with PHP in running. However, there is very limited scienti®c evidence available to verify this hypothesis. The results from the current study found no signi®cant difference (P 0.68) in hill-running between nonPHP runners and PHP runners. Running on hard surfaces, such as concrete or soft surfaces such as sand, has been reported with PHP (Ali et al. 1995). However, no statistical evidence was found in the current study. Running on Astroturf may be a substitute or an alternative activity for those runners who had previously suffered or who were currently suffering from high-mileage-induced PHP injuries. Previous injury, de®ned in this study as sustaining a running injury within the previous
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Development of plantar heel pain in athletes
12 months, has been identi®ed consistently as a risk factor for further injury. The results from the current study identi®ed that previous injury was signi®cantly associated with PHP. A critical comment should be made with respect to the way in which previous injury was assessed in this study. At baseline, all subjects were asked without further speci®cation whether or not they had sustained previous PHP problem. If so, this was considered a previous injury. The fact that previous injuries were only registered as such without further speci®cation makes it dif®cult to make a distinction between the recurrence of an old injury, or the occurrence of a new injury. During the nine-month data-collection period, 36 runners reported pain in the heel region that was severe enough to cause the runner to reduce their running distance, consult with a health professional, or use medication. In those subjects with PHP, 55% reported a reoccurrence of PHP. Data from other epidemiological studies on the reoccurrence of injuries, however, are not consistent, ranging from 21 to 70% (Satterthwaite et al. 1999). This large range is probably affected by differences in the de®nition of a recurrent injury and by differences in research methodology However, the fact that previous injury was associated with PHP suggests that preventive measures are important. For example, early recognition of PHP symptoms, subsequent reduction or change of the training load and complete rehabilitation, mean that a sportsperson should only return to unmodi®ed sports if they are free from plantar heel pain. To prevent PHP-running injuries, health education from the clinician is important. The current study highlighted that, of those subjects who had sustained a previous PHP injury, only 16% visited a health professional. This ®nding provides strong support for encouraging subjects with previous or current PHP injuries to seek advice from healthprofessionalsbeforeparticipatinginphysical activity. Furthermore, with 24% of subjects having to reduce weekly physical activity, this stresses the importance of complete, controlled rehabilitation of PHP (i.e. under the supervision of health professionals) before a person starts to run again.
Conclusion The clinical implications of this study suggest that clinicians may not have to initiate a stretching
124 The Foot (2001) 11, 119±125
program for patients with PHP since ankle joint dorsi¯exion was not demonstrated to be associated with plantar heel pain. Foot pronation was found not to be signi®cantly associated with PHP. Clinicians should be aware of these problems and perhaps address the bases of foot pronation and its clinical consequences based on individual needs. The busy clinician should be aware that, when dealing with young sporting athletes, there is a need for a foot and ankle assessment to prevent PHP and that a previous history of PHP may indicate that subjects may indeed be prone to further episodes. References Ali S, Gilbert N G, Galloway T R 1995 Plantar fasciitis: a review of the literature. Br J Podiatr Med Surg 7: 61±67 Amis J, Jennings L, Graham D, Graham C E 1988 Painful heel syndrome: radiographic and treatment assessment. Foot Ankle 9: 91±95 Ator B, Gunk K, McPoil T, Knecht T 1991 The effect of adhesive strapping on medial longitudinal arch support before and after exercise. J Orthop Sports Phys Ther 14: 18±23 Caine C G, Caine D J, Lindner K J 1996 The epidemiology of sports injuries. In: Caine C G, Caine D J, Lindner K J (eds) The Epidemiology of Sports Injuries. Human Champaign, IL: Kinetics Publishers Hill R S 1996 Ankle equinus. J Am Podiatr Med Ass 85: 134±156 Hintermann B, Nigg B M, Sommer C 1994 Foot movement and tendon excursion: An in-vitro study. Foot Ankle Int 15: 386±295 Hunt A E, Fahey A J, Smith R M 2000 Static measures of calcaneal deviation and arch angle as predictors of rearfoot motion during walking. Austr J Phys 46: 9±16 James S L, Bates B T, Ostering L R 1978 Injuries to runners. Am J Sport Med 6: 40±50 Kaufman K R, Brodine S K, Shaffer R A et al 1999 The effect of foot structure and range of motion on musculoskeletal overuse injuries. Am J Sports Med 27: 585±593 Kibler W B, Goldberg C, Chandler T J 1991 Functional biomechanical deficits in running athletes with plantar fasciitis. Am J Sport Med 19: 66±71 Krivickas L S 1997 Anatomical factors associated with overuse sports injuries. Sports Med 24: 132±146 Macera C A 1992 Lower extremity injuries in runners. Sports Med 13: 50±57 Marti B 1988 Benefits and risks of running among women: an epidemiological study. Int J Sports Med 9: 92±98 McPoil T G, Brocato R S 1990 The foot and ankle: biomechanical evaluation and treatment. In: Gould J A (ed) Orthopaedic and Sports Physical Therapy. St Louis: CV Mosby, 293±321 Meeuwisse W H 1994 Assessing causation in sport injury: a multifactorial model. Clin J Sport Med 4: 166±170
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Development of plantar heel pain in athletes
Messier S P, Pittala K A 1988 Aetiological factors associated with selected running injuries. Med Sci Sports Exerc 20: 501±505 Neely F G 1998 Intrinsic risk factors for exercise-related lower limb injuries. Sport Med 26: 253±263 Reischl S F, Powers C M, Rao S et al 1999 Relationship between foot pronation and rotation of the tibia and femur during walking. Foot Ankle Int 20: 513±520 Rome K 1996 Ankle joint dorsiflexion measurement studies: a review of the literature. J Am Podiatr Med Ass 5: 205±211 Rome K 1997 Anthropometric and biomechanical risk factors in the development of plantar heel pain. Phys Ther Review 2: 123±134 Root M L, Orien W P, Weed J H 1971 Biomechanical Examination of the Foot. Los Angeles: Clinical Biomechanics Corporation, Satterthwaite P, Norton R, Larmer P et al 1999 Risk factors for injuries and other health problems sustained in a marathon. Br J Sports Med 33: 22±26 Taunton J E, Clement D B, McNicol K 1982 Plantar fasciitis in runners. Canada J App Sport Sci 7: 41±44 Thoms V, Rome K 1997 Effect of subject position on the reliability of measurement of active ankle joint dorsiflexion. Foot 7: 153±158
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Vicenzino B, Feilding J, Howard R, Moore R, Smith S 1997 An investigation of the antipronation effect of two taping methods after application and exercise. Gait Posture 5: 1±5 Vicenzino B, Griffiths S R, Griffiths L A, Hadley A 2000 Effect of antipronation tape and temporary orthotic on vertical navicular height before and after exercise. J Orthop Sports Phys Ther 30: 333±339 Wall J R, Harkness M A, Crawford A 1993 Ultrasound diagnosis of plantar fasciitis. Foot Ankle Int 14: 465±470 Walter S D, Hart L E, McIntosh J M et al 1989 The Ontario cohort study of running-related injuries. Arch Int Med 149: 2561±2564 Warren B L 1984 Anatomical factors associated with predicting plantar fasciitis in long-distance runners. Med Sci Sport Ex 16: 60±63 Warren B L, Jessie-Jones C 1987 Predicting plantar fasciitis in runners. Med Sci Sports Exerc 19: 71±73 Weil L S, Gowlding P B, Nutbrown N J 1994 Heel spur syndrome: a retrospective study of 250 patients undergoing a standardized method of treatment. Foot 4: 69±78
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Risk factors associated with the development of plantar heel pain in athletes Keith Rome, Tracey Howe and Ian Haslock
Keith Rome PhD, MSc, BSc(Hons) DPodM, SRch, Rehabilitation Research Unit, Postgraduate Institute for Health and Social Care, School of Health, University of Teesside, Middlesbrough, UK TS1 3BA. E-mail: [email protected]. uk; Tel.: 44 (0) 16 42 384977; Fax: 44 (0) 1642 384105 Tracey Howe PhD, MSc, GradDipPhys, Director of Postgraduate Institute for Health and Social Care, Rehabilitation Research Unit, School of Health, Physiotherapy, University of Teesside Ian Haslock FRCP, MD, Rheumatology Department, South Cleveland Hospital, Middlesbrough, UK
The aetiology of plantar heel pain-running injuries is controversial, with conflicting evidence pertaining to its development. A cross-sectional design was used to calculate prevalence rates and the association of risk factors with plantar heel pain (PHP). One hundred and sixty-six subjects (mean age 23.9, SD 7.1 years) were assessed. A prevalence rate of 21.7% was determined. Independent t-tests and w2 analysis evaluated the association between the risk factors and PHP at the 5% level. The results demonstrated that young age and previous injury were significantly associated with PHP (P < 0.05), and all other risk factors were non-significant (P < 0.05). The results demonstrated that traditional risk factors such as excessive foot pronation, ankle equinus, and body weight are not associated with PHP. Recommendations include regular clinical evaluation of athletes with a history of PHP to prevent reoccurrence. ß 2001 Harcourt Publishers Ltd
Introduction Plantar heel pain (PHP) in runners has been described as an overuse injury associated with the accumulation of repetitive force over time rather than a single traumatic event (Krivickas 1997). The heterogeneity of disorders grouped together as plantar heel pain makes it dif®cult to unravel its de®nitive aetiology, and there appears to be a variety of controversial theories as to the actual cause of PHP (Ali et al. 1995). Many factors that may possibly in¯uence risk of injury have been previously been identi®ed (Neely 1998). These factors are commonly referred to as risk factors and have been classi®ed as intrinsic or extrinsic (Caine et al. 1996). Intrinsic risk factors are individual anatomical and biological characteristics predisposing a person to the outcome of injury, while extrinsic risk factors have an effect on the sport participant `from without' (Table 1). Meeuwisse (1994) proposed that intrinsic factors are factors which predispose the runner to
119 The Foot (2001) 11, 119±125
doi: 10.1054/foot.2001.0698, available online at http://www.idealibrary.com on
react in a speci®c manner to an injury situation. However, once the runner is predisposed, extrinsic factors such as previous injuries may facilitate manifestation of injury, and may interact to make the runner more susceptible to injury. Although risk factors may render the runner more susceptible to injury, they are usually not suf®cient in themselves for an injury to occur. The ®nal element in the web of causation involves an inciting event and injury mechanism. An inciting event may be viewed as a precipitant factor associated with the de®nitive onset of injury, such as running on a slippery surface (Meeuwisse 1994). One of the most widely stated anatomical risk factor associated with PHP is excessive foot pronation (Warren 1984, James et al. 1978, Warren & Jessie-Jones 1987). Limited ankle joint dorsi¯exion range of motion has also been reported to be associated with PHP (Amis et al. 1988, Kibler et al. 1991, Hill 1996). PHP has been reported in subjects 7±85 years old in both the recreational and population-based studies
ß 2001 Harcourt Publishers Ltd
Development of plantar heel pain in athletes
Table 1 Intrinsic and extrinsic risk factors associated with plantar heel pain Extrinsic risk factors
Intrinsic risk factors
Running surface
Biological: age, gender, weight, height
Speed and frequency of running
Anatomical: range of motion at ankle and subtalar joints
Miles run per week Previous injury
(Taunton et al. 1982, Kibler et al. 1991, James et al. 1978). The effect of high or low weight has been examined from several perspectives. In the athletic literature, one study demonstrated no clear evidence of BMI on injury rates (Neely 1998), while other studies have reported a U-shaped relationship such that both the lightest and the heaviest group of runners were at increased risk for injuries (Marti 1988). Previous studies on extrinsic risk factors associated with PHP are limited, although there have been tentative links with the development of PHP with previous injury, running surfaces and past experience (Warren 1984, 1987). A review of the literature suggests that the relationship between intrinsic and extrinsic risk factors associated with PHP is unclear. The aim of the study was to determine the prevalence rate of PHP and to evaluate intrinsic and extrinsic risk factors associated with PHP in a cohort of runners.
Methods To calculate the sample size, a 90% power calculation was performed based upon pilot work on vertical navicular height measurements. The prevalence rate of PHP in the sporting population has been reported to be 8±21% (Rome 1997). Therefore, to achieve a 21% prevalence rate, a sample size of 166 subjects was required. One hundred and thirty subjects were designated into a non-PHP group and 36 subjects diagnosed with PHP. The subjects were conveniently sampled from local athletic clubs and the University sports clubs. All subjects were free to withdraw from the study at any time and informed consent forms were completed prior to entry. The University Ethics Committee approved this study. In the current study, the subjects were de®ned as any sportsperson running regularly as part of
120 The Foot (2001) 11, 119±125
their main physical activity. PHP was de®ned as pain unilateral in nature with at least 2 months' duration that is attributed to physical activity. The subject described either a history of night-time or early morning plantar heel pain, which decreased after walking, and/or increased after exercise or prolonged periods of standing (Wall et al. 1993). The problem had to be severe enough to either cause a reduction in physical activity, a visit to a health professional, or the use of medication. The subject had to be in good general health, with no known history of systemic disease, including rheumatoid arthritis, seronegative arthritis or gout. Exclusion criteria included previous foot surgery, recent abrupt trauma to the foot, congenital defects of the lower extremity, or corticosteroid injection in the heel in the previous 3 months (Wall et al. 1993).
Measurement of foot pronation Foot pronation was measured by using the height of the navicular from a static weight-bearing position. Vertical navicular height is frequently used as a measure of pronation (Vicenzino et al. 2000). To calculate the navicular height, the most prominent palpable portion of the navicular tuberosity was marked with a dot using a ®ne-black felt-tip pen when the subject was prone. The subject stood on a raised platform and was placed in a bilateral weight-bearing stance position. A modi®ed digital caliper (Mitutoyo Ltd, Andover, UK) was used to measure navicular height. The caliper was set to zero prior to measurements, and placed vertically on the inner side of the foot just anterior to the navicular. The distance (in millimetres) from the ®xed end of the caliper to the mark on the navicular tuberosity was measured. An intraclass correlation (ICC) was undertaken to evaluate the reliability of the technique using 20 healthy subjects over two occasions and the results demonstrated good reliability (ICC 0.85). Previous studies have reported similar ®ndings (Ator et al. 1991, Vicenzino et al. 1997).
Measurement of ankle joint dorsiflexion Each subject was in a reclined and fully supported supine position on a padded examination couch with the hip and knee joints fully extended and the lower legs extended over the edge of the couch by
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Development of plantar heel pain in athletes
about 15±18 cm (Thoms & Rome 1997). The ankle joint was measured from a zero starting position. In this case, the subtalar neutral position was chosen as it is the most commonly recommended within clinical practice (Rome 1996). The method used to obtain this neutral position was by palpation of the congruency of the talar head (McPoil & Brocato 1990). From the zero position, the subject dorsi¯exed the ankle as far as possible, and was then asked to maintain this position until the ®rst measurement was obtained. Three measurements were taken and the mean (SD) were calculated for each set of three measurements.
Measurement of biological factors Body mass index (BMI) was calculated using the equation weight/height2, a method commonly used to evaluate an increase or decrease in body weight. Height and weight were also examined independently using calibrated instrumentation. Age was strati®ed into adolescents (14±19 years old) and adults ( $ 20 years old). Pilot work demonstrated that stratifying subjects into 10-year age bands (10±19; 20±29; 30±39; 40±49; > 50 years old) proved to be dif®cult, because the subject groups were too small for analysis. Collapsing cells into the two categorical groups allowed appropriate w2 analysis.
Data analysis Data were analyzed using SPSS for Windows and involved independent t-tests or w2 analysis of each risk factor to evaluate any signi®cant differences between PHP and non-PHP groups, at the 5% level. Ankle joint dorsi¯exion measurements were further strati®ed into subjects with less than 108 of dorsi¯exion from a zero position (ankle equinus) and those above 108 of ankle joint dorsi¯exion as is commonly indicated in clinical practice (Root et al. 1971).
Results Thirty-six subjects were diagnosed with PHP, producing a prevalence rate of 21.7%. Baseline characteristics demonstrated that PHP subjects ran for an average of 13.1 miles week, while non-PHP subjects ran for an average of 12.1 miles per week (Table 2). Signi®cant differences were demonstrated between previous injuries (P 0.001) and PHP. All other factors associated with a running history were non-signi®cant. Twenty-nine per cent (29%) of those subjects with PHP reported pain when standing for long periods, with 15% reporting PHP increasing in the cold weather. Fifty-three per cent (53%) of subjects reported PHP when standing on tiptoe or experiencing pain in the ®rst 50±100 steps. Approximately one-quarter (24%) of those subjects
Sporting history Baseline characteristics of the cohort were collated using a self-administered questionnaire at the time of baseline data collection. This method of collection ensures a high response rate, accurate sampling and a minimum of interviewer bias, while permitting interviewer assessments, providing necessary explanations and giving the bene®t of a degree of personal contact. Pilot work involving content and face validity were used to construct the questionnaire. The topic areas were constructed from previous literature, physical ®ndings, and clinical observation relating to lower limb sports injuries. Speci®c questions relating to PHP running history, which included running speed, previous injury, running experience, and miles run per week, were constructed from previous studies (Warren 1984, Warren & Jessie-Jones 1987, Wall et al. 1993, Weil et al. 1994).
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Table 2 Baseline characteristics of study participants P-value Years running
0.60
Reasons for running
0.66
Type of training
0.44
Previous injuries
0.01
Type of running surface Hill terrain
0.68
Concrete
0.17
Asphalt
0.39
Grass
0.92
Astroturf or other synthetic surface
0.76
Cambered
0.45
Miles run per week
0.25
Speed (miles/min)
0.28
Significant at the 5% level.
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Table 3 Means (standard deviations) and statistical analysis of independent variables in the two plantar heel pain groups Independent variables
PHP group (n 36) Mean (SD)
Non-PHP group (n 130) Mean (SD)
P-value
Age (years)
24.6 (7.7)
21.7 (5.1)
0.01*
Ankle dorsiflexion (8)
16.0 (5.8)
15.9 (6.3)
0.39
Ankle equinus (<108)
7.7 (1.9)
7.2 (1.6)
0.30
32.7 (7.0)
31.5 (7.3)
0.37
23.14 (3.3)
23.23 (2.8)
0.91
1.73 (0.1)
1.75 (0.1)
0.31
69.45 (12.1)
71.53 (12.4)
0.31
Navicular height (mm) 2
BMI (weight /metre ) Height (m) Weight (Kg) At 5% significant level.
with PHP reported a reduction in weekly physical activity, with 16% reported visiting a health professional and only 9% took medication for PHP. Only 13% of subjects reported to have been given a medical diagnosis. No subjects reported having steroid injections for heel pain in the last 12 months. The results demonstrated no signi®cant differences (P 0.39) in ankle joint dorsi¯exion between PHP and non-PHP groups (Table 3). Even adjusting for ankle equinus, there was no signi®cant difference between PHP and non-PHP groups (P 0.78). There was no signi®cant difference in excessive foot pronation between PHP and non-PHP groups using the navicular height technique (P 0.37) or accounting for foot length (P 0.34). The results also found no signi®cant difference in height (P 0.31), weight (P 0.93), and BMI (P 0.56) between the PHP and non-PHP groups.
Discussion The results from the current study suggest that foot pronation is not associated with PHP in runners. Other epidemiological studies have found similar evidence (Kaufman et al. 1999, Hunt et al. 2000). It has been suggested from the literature that a combination of foot pronation and substantial movement transfer of the foot into internal tibial rotation is a better predictor of the development of overuse injuries (Hintermann et al. 1994). The excessive foot pronation may therefore have a secondary effect on the lower extremities, such as an increased compensatory internal rotation of the tibia which may predispose individuals to overloading stress on the medial aspect of
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the foot and cause PHP. Increased rotation of the tibia may also give more proximal effects through the femur and the pelvis. However, recent work have suggested that the relationship between foot pronation, lower extremity kinematics ± in particular increased rotation of the tibia ± and clinical symptoms must be viewed with caution and evaluated on a patient-by-patient basis rather than with reference to the sporting or general population (Reischl et al. 1999). The results from the current study demonstrated that ankle joint dorsi¯exion was not associated with PHP. Further analysis using the standard 108 as a reference point demonstrated no signi®cant differences (P 0.96) between the PHP and non-PHP groups, suggesting that limited ankle joint dorsi¯exion is not associated with the development of PHP. Common clinical practice states that a minimum of 108 of ankle joint dorsi¯exion is necessary for normal locomotion. If subjects have less than this minimum requirement, then this could lead to functional ankle equinus (Root et al. 1971). Although the current study found no signi®cant difference between the PHP groups using the criterion of less than 108 dorsi¯exion, subjects may have been able to compensate for insuf®cient ankle dorsi¯exion in a variety of ways. Some subjects may compensate by decreasing step length, while others have a symmetrical and normal step length but have hypermobile dorsi¯exion of the forefoot on the rearfoot. Another compensation is an increase in the toe-out foot placement angle, so that ankle dorsi¯exion demands during late stance phase of the gait cycle are decreased (Hill 1996).
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Development of plantar heel pain in athletes
Alterations in BMI have been implicated as risk factors in the development of PHP. Subjects with high BMI may have excessive biomechanical and physiological stresses on their musculoskeletal system because of the extra weight. Those subjects with a low BMI may not have enough lean body mass to support their weight during the stresses of vigorous physical activity. However, the current study demonstrated that BMI was not signi®cantly associated with PHP, suggesting that BMI is therefore not a risk factor associated with PHP in runners. The results demonstrated that age was signi®cantly associated with PHP, which was somewhat surprising. The majority of young adults either attended University or local athletic clubs and participated in weekly and daily athletic training. One can postulate that younger runners may indeed to be more prone to the development of PHP than older runners. Younger runners possibly train at higher speeds and run more miles per week than older runners. The lower prevalence in adult respondents, who were relatively fewer in numbers, may represent a survival phenomenon where, if a runner is still running at an older age, it is because they have survived the injuries that cause many runners to leave the sport. Previous PHP running studies (Taunton et al. 1982, Warren 1984) have implicated excessive mileage as a cause of PHP in runners, although the results from the current study demonstrated no statistically signi®cant difference in overall mean distance per week between PHP group and non-PHP group. Furthermore, 48% of PHP subjects were running for less than 20 miles per week, and only 2% of the PHP subjects were running more than 80 miles per week. This ®nding is supported by several studies which suggest that total weekly mileage alone cannot explain injury patterns (James et al. 1978, Messier & Pittala 1988). The runners with PHP in this study ran on average 2.2 times per week for 13.1 miles per week at a speed less than 8 min/mile. Non-PHP subjects ran on average 1.9 times per week for 12.1 miles at a speed less than 8 min/mile. If compared with the populations of other studies (Walter et al. 1989, Macera 1992), the average subject in the current study can be considered as representing the recreational runner who runs for pleasure and health rather than for competition, and who participates in other physical activity.
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The variable ®tness levels or experience of the subjects may confound the inconclusive information about the in¯uence of exposure on PHP rates in physical activity. Previous studies have suggested that runners who have been running for less than three years or who are generally inexperienced may be at a greater risk of injury (Marti 1988, Macera 1992). However, the data from the current study suggest that running experience is not a risk factor for developing PHP. The present study encompassed a wide range of ability, from elite, nationally ranked runners to casual, ®rst- time runners. Subjects used in previous PHP studies have been limited to very speci®c populations either participating in marathons or road races, or have consisted of habitual runners. This limits the application of results to a speci®c type of runner across a larger population. To the authors' knowledge, this paper describes the ®rst study to examine runners who run but who do not compete in marathons or road races. Likewise, previous studies which conducted case series designs only evaluated runners who went to seek medical advice from a health professional or sports injury clinic and did not consider runners who were injured and did not seek treatment (Taunton et al. 1982, Warren 1984). Consequently, PHP running studies are negatively affected by sampling and non-random selection of subjects. Physical activity mostly takes place in an outdoor environment and is subject to a great deal of in¯uence by weather, running surfaces, and running terrain. Running injury has been attributed to a change in running surface, in particular hill-running, which has been commonly quoted as a risk factor associated with PHP in running. However, there is very limited scienti®c evidence available to verify this hypothesis. The results from the current study found no signi®cant difference (P 0.68) in hill-running between nonPHP runners and PHP runners. Running on hard surfaces, such as concrete or soft surfaces such as sand, has been reported with PHP (Ali et al. 1995). However, no statistical evidence was found in the current study. Running on Astroturf may be a substitute or an alternative activity for those runners who had previously suffered or who were currently suffering from high-mileage-induced PHP injuries. Previous injury, de®ned in this study as sustaining a running injury within the previous
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Development of plantar heel pain in athletes
12 months, has been identi®ed consistently as a risk factor for further injury. The results from the current study identi®ed that previous injury was signi®cantly associated with PHP. A critical comment should be made with respect to the way in which previous injury was assessed in this study. At baseline, all subjects were asked without further speci®cation whether or not they had sustained previous PHP problem. If so, this was considered a previous injury. The fact that previous injuries were only registered as such without further speci®cation makes it dif®cult to make a distinction between the recurrence of an old injury, or the occurrence of a new injury. During the nine-month data-collection period, 36 runners reported pain in the heel region that was severe enough to cause the runner to reduce their running distance, consult with a health professional, or use medication. In those subjects with PHP, 55% reported a reoccurrence of PHP. Data from other epidemiological studies on the reoccurrence of injuries, however, are not consistent, ranging from 21 to 70% (Satterthwaite et al. 1999). This large range is probably affected by differences in the de®nition of a recurrent injury and by differences in research methodology However, the fact that previous injury was associated with PHP suggests that preventive measures are important. For example, early recognition of PHP symptoms, subsequent reduction or change of the training load and complete rehabilitation, mean that a sportsperson should only return to unmodi®ed sports if they are free from plantar heel pain. To prevent PHP-running injuries, health education from the clinician is important. The current study highlighted that, of those subjects who had sustained a previous PHP injury, only 16% visited a health professional. This ®nding provides strong support for encouraging subjects with previous or current PHP injuries to seek advice from healthprofessionalsbeforeparticipatinginphysical activity. Furthermore, with 24% of subjects having to reduce weekly physical activity, this stresses the importance of complete, controlled rehabilitation of PHP (i.e. under the supervision of health professionals) before a person starts to run again.
Conclusion The clinical implications of this study suggest that clinicians may not have to initiate a stretching
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program for patients with PHP since ankle joint dorsi¯exion was not demonstrated to be associated with plantar heel pain. Foot pronation was found not to be signi®cantly associated with PHP. Clinicians should be aware of these problems and perhaps address the bases of foot pronation and its clinical consequences based on individual needs. The busy clinician should be aware that, when dealing with young sporting athletes, there is a need for a foot and ankle assessment to prevent PHP and that a previous history of PHP may indicate that subjects may indeed be prone to further episodes. References Ali S, Gilbert N G, Galloway T R 1995 Plantar fasciitis: a review of the literature. Br J Podiatr Med Surg 7: 61±67 Amis J, Jennings L, Graham D, Graham C E 1988 Painful heel syndrome: radiographic and treatment assessment. Foot Ankle 9: 91±95 Ator B, Gunk K, McPoil T, Knecht T 1991 The effect of adhesive strapping on medial longitudinal arch support before and after exercise. J Orthop Sports Phys Ther 14: 18±23 Caine C G, Caine D J, Lindner K J 1996 The epidemiology of sports injuries. In: Caine C G, Caine D J, Lindner K J (eds) The Epidemiology of Sports Injuries. Human Champaign, IL: Kinetics Publishers Hill R S 1996 Ankle equinus. J Am Podiatr Med Ass 85: 134±156 Hintermann B, Nigg B M, Sommer C 1994 Foot movement and tendon excursion: An in-vitro study. Foot Ankle Int 15: 386±295 Hunt A E, Fahey A J, Smith R M 2000 Static measures of calcaneal deviation and arch angle as predictors of rearfoot motion during walking. Austr J Phys 46: 9±16 James S L, Bates B T, Ostering L R 1978 Injuries to runners. Am J Sport Med 6: 40±50 Kaufman K R, Brodine S K, Shaffer R A et al 1999 The effect of foot structure and range of motion on musculoskeletal overuse injuries. Am J Sports Med 27: 585±593 Kibler W B, Goldberg C, Chandler T J 1991 Functional biomechanical deficits in running athletes with plantar fasciitis. Am J Sport Med 19: 66±71 Krivickas L S 1997 Anatomical factors associated with overuse sports injuries. Sports Med 24: 132±146 Macera C A 1992 Lower extremity injuries in runners. Sports Med 13: 50±57 Marti B 1988 Benefits and risks of running among women: an epidemiological study. Int J Sports Med 9: 92±98 McPoil T G, Brocato R S 1990 The foot and ankle: biomechanical evaluation and treatment. In: Gould J A (ed) Orthopaedic and Sports Physical Therapy. St Louis: CV Mosby, 293±321 Meeuwisse W H 1994 Assessing causation in sport injury: a multifactorial model. Clin J Sport Med 4: 166±170
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