Journal of the American Podiatric Medical Association @BULLET Vol 94 @BULLET No 3 @BULLET May/ A Theory of Shoe Wear Pattern Influence Incorporating a New Paradigm for the Podiatric Medical Profession

Journal of the American Podiatric Medical Association @BULLET Vol 94 @BULLET No 3 @BULLET May/ A Theory of Shoe Wear Pattern Influence Incorporating a New Paradigm for the Podiatric Medical Profession
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  Journal of the American Podiatric Medical Association • Vol 94 • No 3 • May/June 2004261 Podiatric physicians hold the traditional belief thatshoe wear patterns have diagnostic significance andthat given foot pathologic entities create specificcharacteristic wear patterns on the shoe outsole asthe shoe becomes progressively worn. 1-6 This belief can be summarized as a “one condition, one wear  pattern” hypothesis. Recent work, however, has castdoubt on this belief. In a previous Delphi study § of  podiatric physicians’ experiences of shoe wear pat-terns, participants reported that multiple patternforms were associated with single foot pathologies. 7-9  Although this Delphi study eventually led to agree-ment among participants that certain patterns couldbe characteristic of specific pathologies, the wider range of patterns reported had been observed in practice and were therefore possible. It was believedthat the agreements reached related only to the mostcommonly observed patterns. A Theory of Shoe Wear Pattern InfluenceIncorporating a New Paradigm for thePodiatric Medical Profession Wesley Vernon, PhD, DPodM*Anne Parry, PhD†Michael Potter, MSc‡ Qualitative analysis of shoe wear patterns collected from a question-naire evaluating podiatric physicians’ experiences in this area sug-gests that wear patterns could indicate causative function within aknown pathologic context. Several different functions are suggested bypatterns associated with each of the pathologic entities involved, andanalysis of the relationship between patterns and reasons given by re-spondents for pattern-form variations show the strongest associationsto be with functionally termed conditions. A basic model is proposed topresent factors important in wear pattern production, suggesting that anew concept of primary walking intention is more influential than footpathologies in wear pattern formation and that external factors are alsoinfluential, with the combined factors being described as the “holisticfoot function.” This model may provide a variety of benefits to podiatricmedicine; as shoe wear patterns are records of the usual long-term ac-tivity of the functioning foot, this paradigm could form a basis for podi-atric medical practice.(J Am Podiatr Med Assoc 94(3): 261-268, 2004) *Podiatry Service, Community Health Sheffield, Sheffield,England.†School of Health and Community Studies, Sheffield Hal-lam University, Sheffield, England.‡Podiatry Research Group, School of Health Professionsand Rehabilitation Sciences, University of Southampton,Southampton, England. Corresponding author: Wesley Vernon, PhD, DPodM, Po-diatryService, Community Health Sheffield, Centenary House,Heritage Park, 55 Albert Terrace Rd, Sheffield S6 3BR, Eng-land. PODIATRIC RESEARCH FROM THE UNITED KINGDOM §A Delphi study is one based on a communication pro-cess designed to enable a group of individuals as a wholeto address a complex problem. Involving several rounds of questionnaires completed by the same group of experts, itsfeatures include anonymity, feedback, statistical group re-sponse, use of informed respondents, and group consensus.  262May/June 2004 • Vol 94 • No 3 • Journal of the American Podiatric Medical Association To understand the meaning of this position, and tolearn more about the relationship between shoe wear  patterns and foot pathologic entities, a qualitativeanalysis of wear pattern associations with namedfoot pathologies was planned. If greater understanding of the link between shoe wear patterns and foot functioncould be gained, then shoe wear patterns may proveto have clinical value despite the recent doubts 7-9 caston this possibility. As shoe wear patterns may be a record of the usual long-term activity of the foot,study of them could provide new insights into footfunction and influences on it. Such a study has the potential to generate new knowledge that will be of benefit to the practice of podiatric medicine. Attempts have been made to understand shoewear patterns in a forensic identification context, 6, 10 but without success. 11 Greater understanding may,therefore, also improve the value of shoe wear pat-tern use in identification methods, leading to a wider range of identification techniques and the preventionof problems experienced through misconceptions. 11 The Focal Point Method of Wear Pattern Description and Comparison The focal point method of pattern comparison arosefrom the earlier Delphi study of shoe wear patterns. 8 In this study, it was suggested that wear patternscould be usefully described and compared in relationto the points from which the various components of wear spread. An instrument was created to capturethese focal points, with identifying numbers assignedto each point (Fig. 1). Early work suggests that it is a useful tool for comparison of shoe wear patternswith the capability of excluding secondary variablescaused by factors such as age of footwear. 12  A studywas designed to gather more information to refinethe tool and enhance the interpretation of wear pat-tern data. The aims of this study were to collect, ana-lyze, and interpret podiatric physicians’ observationsof shoe wear patterns; to identify associations be-tween wear patterns and named pathologies; and to propose theoretical themes linking wear patternsand pathologies. Methods  An explanation of the methodologic considerationsunderpinning the approach adopted is given in Ap- pendix 1. A short preliminary questionnaire indicatedthe conditions for which podiatric physicians be-lieved they had the greatest understanding of wear  patterns: pronation, hallux rigidus, pes cavus, andrearfoot varus. A questionnaire was designed to col-lect data about shoe wear pattern depictions basedon these four conditions to optimize the potential re-sponse. All known heads of National Health Service podi-atric medical services in the United Kingdom weresent a letter asking them to forward a questionnaire package to the staff member with the greatest shoewear pattern interpretation expertise. There is nodefinition of a podiatric physician with shoe wear ex- pertise, but working clinicians have been used as ex- perts in several earlier studies. 13-16 First contact withthe service head echoed that in the study by Reed, 17 where a similar selection method eliminated re-searcherbias by avoiding participant preselection.The questionnaire package included explanatorynotes, an example sheet, and the questionnaire itself.To ensure freedom of expression without inhibition,respondents were offered complete anonymity. Theywere asked to sketch wear patterns with which theywere familiar on blank outsole outlines for prona-tion, hallux rigidus, pes cavus, and rearfoot varus. Itwas stressed that the patterns should be based onlong and varied observation rather than on a singleobservation for the purpose of completing the ques-tionnaire. As it was believed that each conditioncould generate several different patterns, respon-dents could suggest more than one pattern for eachcondition and state the reason for each variation (eg,gait deviations or presence of additional pathologies).Respondents were asked to return the completed Figure 1. Instrument for the description and compari-son of shoe wear patterns. 212017151610111294563218719181413  Journal of the American Podiatric Medical Association • Vol 94 • No 3 • May/June 2004263 questionnaires within 3 weeks of receipt by stamped,self-addressed envelope. A qualitative approach to analysis was seen as thestrategy of choice because shoe wear patterns seemto have a complex and multivariable relationshipwith the foot and its pathologies 7-9 and because thereis no published research on shoe wear pattern forma-tion. It has been argued that pictorial sources “aretexts which can be interpreted and assessed like anyother text.” 18 The wear patterns collected in the mainquestionnaire, therefore, were seen as suitable for in-ductive analysis, with previous unitization to defineand separate units of data for the analysis. 19 The in-ductive analysis sought patterns, themes, and cate-gories from the data, from which interpretive under-standing was sought. 20 Results Overview of the Returned Patterns Fifty-six (26%) of 214 questionnaires were returned. A total of 425 wear patterns resulted, representing a mean of 106.25 patterns for each pathology and a mean of 7.6 patterns (1.9 per condition) for each re-spondent (Table 1). This confirmed that multiple pat-tern forms were associated with single named path-ologies, contrary to previously implied beliefs.Wide pattern variations were seen across theoverall pattern forms (face level) and when consider-ing the patterns on the basis of focal points (focal point level). Respondents suggested many differentreasons for pattern variations (Table 2), includingfunctional differences, neurologic effects, and fac-tors affecting the integrity of the foot. This reflects a complex situation with many potential influences onshoe wear patterns. Although respondents had beenasked to provide depictions of patterns based on ex- perience, there was evidence that some respondentsmay have used direct patient observations instead.Such patterns still have a basis in reality, althoughuse of direct observation suggests low confidence inwear pattern interpretation and understanding. Analysis Qualitative analysis of the returned patterns was un-dertaken to identify themes and relationships be-tween the patterns and associated pathologic entitiesto suggest how the wear patterns are produced in re-lation to these pathologies. Two approaches wereadopted: 1) categorizing the patterns initially by main pathology and then by pattern form to seek associa-tions between pattern form and main pathology; and2) categorizing the patterns initially by named vari-ables (ie, reasons for pattern variations), where given,and then by pattern form to seek associations be-tween named variables and pattern forms. If themesof association with variable factors that may influ-ence shoe wear pattern formation could be identi-fied, theories relating to dominant factors in wear  pattern production could be induced.Using the four main pathologies as initial cate-gories, patterns were divided into subcategoriesbased on predominant focal code wear pattern de-scriptions (Fig. 2), giving multiple focal code–basedsubcategories of wear pattern forms. It was foundthat within the main pathology context, the associat-ed pattern forms indicated that certain foot functionshad taken place to produce that pattern. Thus each pathology by definition suggested that certain prede-fined states were present in the foot. These statescould represent restrictions (eg, the inability of thefirst metatarsophalangeal joint to dorsiflex in halluxrigidus) or incompetence (eg, the inability of the toesto assist in the push-off phase of walking, with re-tracted toes). Given these factors, functions that had produced the patterns could be suggested, with thefollowing components of understanding being essen-tial to this awareness:•A means of wear pattern description—the focal point concept Table 1. Patterns Given for Each Pathology Derived fromShoe Wear Pattern Questionnaire Total NumberMean Number of PatternsConditionof Patternsper RespondentPronation1292.3Hallux rigidus851.5Pes cavus1041.9Rearfoot varus1071.9 Total4257.6Table 2. Named Variables (Reasons Given for PatternVariations) in Shoe Wear Pattern Questionnaire Number of Second-Named Main ConditionConditions GivenPronation71Hallux rigidus32Pes cavus49Rearfoot varus49 Total201  264May/June 2004 • Vol 94 • No 3 • Journal of the American Podiatric Medical Association •Subcategories of pattern forms•Knowledge of foot pathology definitions•Knowledge of normal foot function•Knowledge of foot anatomy•Knowledge that wear patterns must be functionallycausedThrough this process, various function categorieswere suggested for each pathology, with 16 alternativefunctions being suggested for pronation, 14 for halluxrigidus, 18 for pes cavus, and 13 for rearfoot varus. Overall Foot Function as the Primary Shoe Wear Influence The number of different functions suggested for eachmain pathology challenged previous perceptions of more limited functional possibilities. This challengealso suggested how the implied “one condition, onewear pattern” theory had arisen. If only one overallfunction had been anticipated with a foot pathology,only one pattern form would be expected. If, in reali-ty, multiple functions were operating, then multiple pattern forms, such as those observed, would occur.In the example of hallux rigidus, a “classic” shoewear pattern had previously been described. 6 It hadbeen believed that in the presence of hallux rigidus,the forefoot supinates to avoid the stiffened first toerestriction. 21 This function could be linked to theclassic hallux rigidus wear pattern by considering theactions involved. A normal heel strike would pro-duce normal posterolateral heel wear. A stiffenedfirst toe could inhibit wear at the first metatarsopha-langeal joint area by exerting a splinting effect. Thestiff first toe could then provide an oblique axis withthe fifth metatarsophalangeal joint as the foot supi-nates to avoid the first toe restriction, with resultantforefoot shoe wear relating to that axis. The per-ceived absence of alternative functions would haverestricted wear patterns related to hallux rigidus to Figure 2. Example of inductive analysis of wear patterns by pathology and pattern form. A, Pattern forms re-ceived, with identifying codes based on main associated foot pathologies. Secondary associated pathologies arenamed, and focal codes used to describe the pattern are given. B, The process followed in the inductive analysisof the received data. The patterns are initially categorized by the main pathologies given and then are subcatego-rized according to the predominant focal code combinations, which represent the overriding form of the patterns.These categories are further divided according to the full focal code combinations given and, finally, by the associ-ated secondary pathology variables. Abbreviations: I/D, identifier; HR, hallux rigidus; FPCode, focal point code;Pron, pronation. I/D HR 11/2Sub Theme: SupinationFPCode: 1/6/13/18/19I/D HR 16/1Sub Theme: NoneFPCode: 1/14/15/20I/D HR 20/1Sub Theme: NoneFPCode: 1/14/15/20I/D Pron 11/2Sub Theme: Rearfoot ValgusFPCode: 4/16/17I/D Pron 5/2Sub Theme:Rearfoot ValgusFPCode: 4/16/17A. Patterns GivenB. Division of Patterns by CategoryPattern Reference1. Pathology2. Focal Code Predominance3. Detailed Focal Code4. Variable GivenCategoriesCategoriesCategoriesPron 5/2Pronation16/174/16/17Rearfoot ValgusPron 11/24/16/17Rearfoot ValgusHR 11/2Hallux13/18/191/6/13/18/19SupinationHR 16/1Rigidus14/15/201/14/15/20–HR 20/11/14/15/20–  Journal of the American Podiatric Medical Association • Vol 94 • No 3 • May/June 2004265 those associated with this function alone. More re-cently, the possibility of other functions being pres-ent with hallux rigidus and hallux limitus has beenconsidered, 22-24 all based on considering compensa-tions for first-ray sagittal plane restriction. The func-tions described were among those suggested by theshoe wear patterns here, which indicated even morefunctional possibilities.Classifying the patterns by indicative function sug-gested, through the number of patterns involved, thatsome functions occur more commonly than others.This finding could further account for the past mis-conceptions expressed in the “one condition, onewear pattern” hypothesis, as the greater experiencewould have been with the more commonly encoun-tered pattern forms. Foot Pathology as a Secondary Shoe Wear Influence  Although there were strong indications that footfunction was the main influence in shoe wear patternformation, there were also signs that foot pathologycould have a direct but local effect on wear patternsby amending the intended function. In the commonlydescribed hallux rigidus function, which can be seenas “classic,” 21, 25, 26 the local effect of a stiffened firsttoe forces inversion of the foot, which inhibits firstmetatarsophalangeal joint area wear of the outsole.Similarly, with pes cavus, localized first and fifthmetatarsophalangeal joint area wear of the outsoleoccurred with associated plantarflexion of theserays. The influence of local pathology, however,often seemed to be overridden by purely functionalconsiderations. In hallux rigidus, this was seen withthe named variable abducted gait. Here, absent firstmetatarsophalangeal joint wear anticipated with thestiffened first toe was not seen. Instead, the patternsuggested that the foot avoided the first toe restric-tion by rolling over the medial aspect of the forefoot.Despite the suggestion that overall function has a strong relationship with shoe wear patterns, some of the named variables present had strong associationswith localized areas of shoe wear. In some cases, thissuggested that foot pathology could exert a directbut local influence over wear patterns (eg, a plan-tarflexed first ray showed a strong association withfirst metatarsophalangeal joint wear). Although over-all function had the greatest effect on wear, it seemedthat foot pathologies could also demonstrate wear in-fluence, albeit on a localized basis.It could be considered that the foot attempts tocarry out a particular function, which may then beamended by the effects of local pathology. The at-tempted function could be described as a “primarywalking intention.” The actual function producedafter being subjected to the effect of other influencescould be considered an overall “holistic” function.Where there are no such amendments to the primarywalking intention, this in itself would constitute theholistic function. The Potential for External Influence on Shoe Wear Patterns Within the suggested function categories, depictionsshowing minor wear differences were noted relatingto heel wear angle variations, tip wear inclusion, siteof first toe area wear, and peripheral spread of wear. Although many of these variations may relate tominor functional variations or pattern depiction inac-curacies, other external influences may be involved.It has previously been suggested, for example, thatfootwear variables could be responsible for wear pat-tern amendments 1, 3, 4, 27 and that occupational factorssuch as driving and machinery operation could con-ceivably have an effect on outsole wear. External variable effects were not reported by the respondentsand may, therefore, be minor, unappreciated, infre-quent, or absent. Such effects, which may include fea-tures such as shoe fit and occupational factors (Fig.3), could corrupt the primary walking intention andmay, therefore, contribute to overall function. Astheir effect seemed to be minor or infrequent, these variables are suggested to be less influential than foot pathologies in wear pattern formation. A basic modelwas proposed to suggest the relationship among fac-tors that influence wear (Fig. 4). A Theory of Shoe Wear Pattern Influence The combined effect of primary walking intention,foot pathology, and external influence can be seen ascreating an overall holistic function. As shoe wear  patterns are records of the usual long-term activity of the functioning foot, this paradigm could form thebasis of a new model for podiatric medicine. A state-ment encapsulating these theories can be derived: Shoe outsole patterns seem to result primarily fromfoot and lower-limb function, and this function isrepresented by combinations of focal points of wear:the areas from which the wear spreads. Although an-atomical and morphologic factors (including foot pathologies) may influence wear, this is throughtheir effect on the primary walking intention. Exter-nal factors may also influence the wear pattern, buttheir effect is usually minor. Wear extending beyondfocal points is superfluous to such interpretation.
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