Craig b. payne the past, present and future of podiatric biomechanics (japma, 1998)


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Craig b. payne the past, present and future of podiatric biomechanics (japma, 1998)

  1. 1. The Past, Present, and Future ofPodiatric Biomechanics CRAIG B. PAYNE, DipPod(NZ), MPH*The author places the history and development of podiatric biomechan-ics, as well as current thinking about its underpinnings and future, in thecontext of a theoretical framework drawn from the philosophy and soci-ology of science. This analysis sets the stage for an exploration of thepossible future directions in which podiatric biomechanics could develop.(J Am Podiatr Med Assoc 88(2): 53-63, 1998)In order to look ahead in the field of podiatric biome- chanics that deals specifically with the interactionschanics, it is necessary to understand the past. The of the foot with the lower extremity.3 However, thephilosophy, sociology, and history of science provide use of the adjective “podiatric” before “biomechan-conceptual frameworks that can be used to explain ics” refers here to the particular “brand” of biome-changes that have occurred in podiatric medical chanics that is commonly used in podiatric medicalpractice and serve as guides to the future. The pur- practice. Its principles have been widely adopted inpose of this article is to analyze the development of other disciplines.4, 5 Historically, podiatric biome-what is commonly referred to as podiatric biome- chanics as a clinical discipline has developed outsidechanics in the context of one of the main theories of the mainstream of the scientific community of bio-the historical development of scientific disciplines. mechanics, itself only one area within the wider sci-This retrospective analysis suggests that it may be ence of biomedical engineering, of which orthopedictime for changes to occur in the clinical practice of biomechanics is considered a part.6podiatric biomechanics. Podiatric biomechanics as it is commonly applied today in clinical practice, in the form of the function-Podiatric Biomechanics al foot orthosis,7, 8 is based on work begun by Root and his colleagues over 30 years ago, with the semi-Few would deny the importance of biomechanics in nal publication, Normal and Abnormal Function ofpodiatric medical practice. Merton L. Root recently the Foot, appearing in 1977.9 Biomechanical princi-wrote: “Biomechanics is a necessary basic science ples were widely taught in podiatric colleges andfor the field of Podiatry. No specialty in the field of continuing-education courses even before publica-medicine is more intimately involved, on an everyday tion of that work.10-12 Other early publications includ-basis, with the clinical application of biomechanics. ed a manual written by Thomas Sgarlato10 used at theThe understanding of basic mechanics and biome- California College of Podiatric Medicine and two ear-chanics of the lower extremity can provide the Podi- lier works by Root et al on clinical examination11 andatrist with an invaluable diagnostic ability that can- neutral-position casting methods.12 After gainingnot be otherwise matched.”1 The term “biomechan- wide acceptance in clinical practice in the US, theics” is frequently misused, but it can be defined as concepts later spread to other countries, including“the application of mechanical laws to living struc- the United Kingdom, 13 Australia, 14 and New Zea-tures, as to a locomotor system.” 2 Podiatric biome- land.15 More recently Root has provided insight intochanics has been defined as that branch of biome- how the functional foot orthosis was developed.16, 17 Before the work of Root and colleagues, there was *Lecturer, Department of Podiatry, La Trobe University, no uniform or widely accepted podiatric theory ofBundoora, Victoria 3083, Australia. foot biomechanics to guide therapy. Early contribu-Volume 88 • Number 2 • February 1998 53
  2. 2. tions to the literature18 include a description in 1845 its wide acceptance and is based on deviations fromby Durlacher19 of a built-up leather inlay used to treat what Root et al considered to be normal alignment.mechanical foot problems. Thomas 20 in 1874 de- Any variation from that normal alignment as theyscribed the use of additions to the outer sole of the defined it was considered to cause abnormal footshoe to treat foot disorders. A different approach function, resulting in a particular set of signs andwas taken in 1888 by Whitman,21 who used a steel su- symptoms, depending on the nature of the variation.pinated device with a high medial and lateral flange The variation is carefully measured,11 and then athat was designed to press on the navicular, causing cast 8, 12, 30 is made of the foot in its neutral position tothe foot to invert by force or from muscular contrac- capture these deviations in alignment. A functionaltion due to pain. Roberts 22 in 1916 developed a metal foot orthosis7, 8, 17 is then constructed, with postsbrace similar to the Whitman device that had a deep attached to position either the forefoot or the rear-inverted heel cup with medial and lateral clips. foot or both in the appropriate alignment, therebyMorton23 in the 1940s advocated the use of an insole restoring what is considered normal function.with a medial forefoot extension to functionally The years since Root et al first elucidated the theorylengthen the first ray. Early contributions from podia- have seen a number of developments, including thetry include that of Schuster,24 who in the 1920s devel- use of extrinsic forefoot posting, 8 application ofoped what became known as the Roberts-Whitman direct pressure on the fourth and fifth metatarsalbrace, which combined features of both devices. heads during the neutral-position casting,8 improve- In 1948, Schreiber and Weinerman25 proposed that ments in materials technology,31 advances in under-an inverted or everted position of the forefoot re- standing of the influence of positional variations inquired balancing. In 1950, Levy26 developed a support the subtalar joint axis,32-34 the medial heel skive tech-combined with a toe crest that became known as the nique,35 the inverted orthosis,36 cast sectioning,37, 38Levy mold; it had a thick leather cover, with the sup- the DC (direct control) inverted wedge,39 the use ofport made of a latex compound. Root later used and scanners 40 to replace the plaster casting process, andmodified this device before moving on to rigid plas- the use of computer technology during the manufac-tics. At this time, the foot tended to be viewed as a ture of orthoses.40, 41static structure, with the height of the arch consid- The widespread application of the principles ofered paramount. More detailed descriptive accounts podiatric biomechanics in clinical practice has notof the historical development of mechanical foot been accompanied by an abundance of publishedtherapy are available elsewhere.18, 27-29 articles in scientific journals describing empirical It is difficult to appreciate the history of a disci- studies. Virtually all of the material in even the mostpline without recognizing the broader context, the recently published textbooks 5, 7, 8, 42, 43 as well as thefactors that have contributed to the shaping of that content of courses offered at podiatric medical col-history. Schuster18 noted that at the turn of the centu- leges and in continuing education programs reflectsry podiatric orthopedics began to develop its own the clinical experience of talented practitioners andunique characteristics because of the limitations on educators. The field is characterized by strongly assert-the scope of podiatric practice, which encouraged an ed opinions that are widely accepted but are unsup-emphasis on mechanical approaches. It was in this ported by data from well-controlled studies or exper-context that Root and his colleagues developed their iments. Often, challenges to these established viewswork, which had a dramatic impact on the clinical are greeted with antagonism 44 and a confusion of factpractice of podiatric medicine. They brought togeth- with theory. Strongly promulgated postulates tend toer a diverse and apparently incoherent body of litera- discourage further work that will enhance understand-ture on foot mechanics and developed the concepts ing. Yet, as the profession develops a more critical atti-of the neutral position of the subtalar joint and the tude toward its underpinnings, the theory is being moreforefoot-rearfoot relationship when the midtarsal systematically and objectively evaluated, and postu-joint is “locked,” while introducing a theoretical lates and assumptions that have become entrenchedcoherence to the field. orthodoxy are increasingly being challenged.45-47 The theory first proposed by Root and his col-leagues as a protocol for the management of foot dis- Philosophy of Scienceorders constituted a dramatic shift in the understand-ing of the foot and its mechanical relationship to the The philosophy of science is concerned with therest of the kinetic chain, emphasizing the foot as a nature and foundations of what is considered to bedynamic rather than a static structure. Their theoreti- scientific knowledge, while the sociology of sciencecal framework has remained largely unchanged since concerns the social processes involved in the pro-54 Journal of the American Podiatric Medical Association
  3. 3. duction of this scientific knowledge. Many philoso- “paradigms” are overthrown and replaced by otherphers and sociologists have proffered theories about paradigms.53-59 His account of the progress of scientif-the development of scientific thought.48-50 The discus- ic inquiry sees science as consisting of long periodssion here, however, is restricted to what is relevant of orderly, disciplined work—which he called “nor-to the field of podiatric biomechanics. The discus- mal science”—punctuated by periods of intellectualsion is admittedly superficial, with no attempt made ferment leading to revolutions in which the old theo-to situate it within the wider debate over the philoso- retical order is overthrown, after which a new periodphy of science. of normal science begins. Normal science is charac- Positivism, once considered the dominant view of terized by the collective acceptance of a certain para-science, holds that science proceeds by means of a digm, or framework of ideas. This set of assumptionsprocess of deriving observational predictions and determines what is considered acceptable “science”hypotheses from theories and then testing them or “practice” at any given time. Practitioners directempirically.48 This process provides the basis for their work toward solving problems that are deter-decisions among competing theories. Scientific mined by or relevant to the dominant paradigm at theknowledge is seen as both rational and objective. time. Kuhn’s central argument is that scientific con-The positivist approach to the historical development cepts must be understood within the particular his-of science assumes that scientific knowledge is in a torical and social context in which they developed.continuous state of accumulation and growth: More This is an appropriate view to adopt for an explo-and more areas are explored, established areas are ration of the history and future course of podiatricexamined in more and more detail, increasingly accu- biomechanics: It can help explain the field’s past asrate observations are made, and increasingly sophis- well as help predict its future.ticated experiments and observations are carriedout. In this way, new concepts and theories to explain A Paradigm in Podiatric Biomechanicsreality evolve, and knowledge grows. The history of aparticular scientific discipline is seen as a linear devel- A paradigm is difficult to define precisely, but itopment toward scientific truth by means of steadily includes scientific laws and theoretical assumptionsimproving scientific methods. In this view, science is as well as how they are applied. Kuhn characterizedfundamentally evolutionary and progressivist. paradigms as “universally recognized achievements, The descriptive accounts of the history of podi- that for a long time provide model problems andatric biomechanics by Schuster18 and Levitz et al27 solutions to a community of practitioners.”51(p176) Theillustrate this positivist approach. For example, paradigm reflects the unique set of beliefs, values,Schuster18 considers the forefoot balancing described and methods shared by this community of practition-by Schreiber and Weinerman25 in 1948 as the prede- ers, a particular worldview that shapes scientificcessor of the forefoot posting developed by Root. thinking and action. Paradigms structure scientificYet, although Root et al 9 cite Schreiber and Weiner- observation in particular ways: Observations areman’s work, there is no evidence that they were made in light of the concepts and theories that areinfluenced by it. Similarly, Starrett 29 claims that the embedded in the paradigm. Kuhn’s theory was con-Whitman device 21 had a profound effect on the devel- ceived as a theory of the history of scientific discov-opment of the modern functional foot orthosis. How- ery, but his original concept of the scientific paradigmever, Blake’s development of the inverted orthotic has since been applied to technological develop-technique was not influenced by the Whitman device ment 60; thus his notion of “paradigm” is very much(R Blake, DPM, personal communication, 1997), applicable to the discipline of podiatric biomechanics.although there are conceptual similarities between The process of the initial formation of a paradigmthe two. Also, while Anthony 8 refers to the influence typically starts with attempts to resolve a particularof the Levy mold on Root’s development of the func- range of problems or develop a body of theoreticaltional orthosis, the functional foot orthosis actually knowledge about some aspect of the world. In thisbears no resemblance to the Levy device. These brief stage, which Kuhn called the “pre-scientific” period,examples suggest that podiatric biomechanics did interpretations of the problem under inquiry are dis-not develop in a linear fashion. organized and diverse. Initial research studies and Historical studies reveal that the evolution of the scientific practice are not structured by any coherentmajor branches of science does not exhibit the struc- model or methodology. Kuhn cites as an example theture assumed by the positivist approach. Kuhn51, 52 wide diversity of theories in optics before Newtoninterpreted the development of scientific knowledge proposed and defended his particle theory. Similarly,as a succession of “revolutions” in which dominant the understanding of podiatric biomechanics beforeVolume 88 • Number 2 • February 1998 55
  4. 4. the advent of Root’s work was not structured or uni- few anomalies is not sufficient to cause the abandon-fied by any coherent model or framework. ment of a paradigm. When many anomalies emerge, The pre-scientific period ends when those engaged however, a state of “crisis” develops, especially if thein this activity form a social community and agree to anomalies pose fundamental challenges to the para-adhere to a single paradigm. The paradigm embodies digm and do not yield to persistent attempts by thethe particular conceptual framework in which the community to resolve them. At that point, the com-practitioners and researchers of that community munity begins to express discontent with the existingoperate and in terms of which a particular interpreta- paradigm, marking the end of the period of “normaltion of “reality” is generated, so that any new theo- science.” According to Kuhn, the anomalies that poseries generated will be consistent with the view of problems for the paradigm result in “pronouncedreality supported by the paradigm. The paradigm sets professional insecurity” among members of the com-the standards for legitimate scientific work and gov- munity. As they begin to lose their faith in the cur-erns the scientific activity of the members of that rent paradigm, debates over fundamental issues arecommunity. The production of theories within a initiated, and alternative paradigms emerge.given paradigm, what Kuhn calls “normal science,” The crisis is finally resolved when the existingusually takes the form of “puzzle-solving,” with the paradigm is abandoned and a new paradigm that haspuzzles always defined by and soluble in terms of the gained the allegiance and support of researchers anddominant paradigm. This period of normal science is practitioners takes its place. This process of “paradigmcharacterized by detailed attempts to articulate the shift” is not based on any rational, systematic, or logi-paradigm, and to improve the match between the cal assessment of the rival alternatives; rather, it is aparadigm and reality, but the fundamentals of the “revolution” brought about by the “conversion” of theparadigm are not questioned. The pre-scientific peri- community. This abandonment of one theoreticalod in the field of podiatric biomechanics essentially structure and its replacement by another one that iscame to an end with the work of Root and his col- incompatible with the first is a key point in Kuhn’sleagues, which was widely accepted by the podiatric structure of scientific revolutions. The new paradigmcommunity as a unifying framework or paradigm then guides normal scientific activity until sufficientthat would guide research and clinical practice. anomalies emerge to result in a new revolution. Disagreement has surfaced in the literature as to Kuhn refers to paradigms as “incommensurable,”whether paradigms are discipline-wide or confined meaning that the overall content and propositions ofto specialties or subfields within a discipline. The different paradigms cannot be directly compared. Con-development of the current paradigm in podiatric clusions drawn within the context of one paradigmbiomechanics would support the argument that they cannot be “translated” into the terms of another par-are confined to specialties or subfields, as that para- adigm. Successive paradigms, then, can be evaluateddigm applies primarily to podiatric management of only with difficulty. Proponents of one paradigm orthe foot, even though, as noted above, some other theory usually have difficulty understanding the pro-disciplines have adopted its underlying principles. ponents of a rival paradigm or theory; thus the twoThe paradigm did not gain wide acceptance in the groups tend to talk past each other. The observationsorthopedic profession for management of the foot; or conclusions drawn by the proponents of a givenindeed, it has been described by members of that paradigm reflect the beliefs, values, and interests ofcommunity as “nonsense and non-science” 61 and is the community that adheres to that paradigm.usually omitted from major orthopedic texts describ- In the early days, resistance to Root’s work cameing foot mechanics.62 from practitioners who tried to relate what he was saying to what they already knew. The problem manyThe Process of Paradigm Shift people have in understanding new paradigms is not necessarily due to any difficulty inherent in the newThe activities that take place during the period of paradigm, but rather relates to the fact that the newnormal science continue as long as the paradigm sat- paradigm is being viewed through the “lens” of theisfactorily explains the phenomena to which it is existing paradigm. This may account for the infa-applied. However, no intellectual framework can mous split between the East Coast and the Westexplain everything. In attempting to discover solu- Coast of the US that occurred in the understandingtions to puzzles, researchers will eventually run into of Root’s original work. Similarities can be seen indifficulties. Puzzles that resist solution are seen with- Constant’s 63 account of the development of the jetin the context of the paradigm as “anomalies” rather engine, in which he relates how aircraft-engine design-than as falsifiers of the paradigm. The existence of a ers strongly adhered to the propeller-driven piston56 Journal of the American Podiatric Medical Association
  5. 5. engine paradigm and were reluctant to take seriously for the propulsive phase of gait. In support of thisany rival system. they cite the analysis of Wright et al70 of two subjects. Yet Root and colleagues appear to have misinterpret-Problems with Traditional Theory ed Wright and colleagues, for what Wright et al called the subtalar joint neutral position is what RootAlthough there has always been a certain amount of et al would consider the relaxed calcaneal stanceresistance to the theories originally proposed by position. Two more recent reports confirmed thatRoot, it paled into insignificance in the context of the the foot is in its relaxed calcaneal stance position,paradigm’s wide acceptance and the extent to which not its neutral position, at midstance during gait.71, 72it was incorporated into clinical practice. With time, Several studies, reviewed by Menz,73 examined thehowever, the number of anomalies or puzzles within reliability of measurement procedures that werethe current podiatric biomechanics paradigm has originally described by Root et al,11 with most findingbecome apparent as attempts have been made to intratester reliability to be reasonably good butimprove the match between the theory and reality. intertester reliability to be poor. This raises major One of the first problems with the theory is not questions about the use of measurement duringreally an anomaly in Kuhnian terms but has led to assessment of patients and for prescription ofdifficulty in understanding of the paradigm. The use orthoses. Three studies74-76 have concluded that staticand intended meaning of certain terms, which were measurements are not good predictors of dynamicoriginally elucidated very clearly by Root et al,11 have limb function. The use of medial foot wedges wasgiven rise to different interpretations and disagree- found to significantly reduce the “Q angle” duringment among practitioners in different disciplines. In static stance but not during gait.77 Static measure-short, what is clear in the podiatric profession is a ments are used as part of the biomechanical assess-source of confusion to those in other fields. ment of patients, but in light of these reports and The definition of “normality” used by Root et al11 other work on the reliability of the measurements,is contentious. It is not compatible with what those their usefulness must be reconsidered. The plasterin the orthopedic profession64 would accept as a cast used for functional foot orthoses is also the prod-“normal” foot, which constitutes a much looser defi- uct of static measurements. One report74 showed anition than the podiatric one. Indeed, the criteria of statistically significant difference between the staticRoot et al might allow the entire population to be and dynamic arch index values, suggesting that theclassified as “abnormal.”45, 46 Reference ranges are traditional method of static casting may not result inwidely used in medicine to determine normality; thus an adequate representation of a dynamic foot. Theit would be expected that the criteria originally pro- assessment of the range of motion of the subtalarposed by Root et al for normalcy would fall in the joint is done in a nonweightbearing position, butmiddle of a normal bell-shaped distribution in a pop- there is a difference between the weightbearing andulation sample. This, however, is not the case.65, 66 nonweightbearing range of excursion of the calca-This is explored by Astrom and Arvidson,66 who con- neus in the frontal plane, indicating motion in thissider the criteria for the normal or ideal foot as joint.78 Many clinicians who are familiar with in-shoedefined by Root et al to be based on an invalid theo- plantar pressure measurements anecdotally reportretical concept. some inconsistency between clinical biomechanical A cornerstone of the Root paradigm is the con- examination and how the foot functions. In particu-cept of subtalar joint neutral position. The intuitive lar, the plantar pressure measurements of patientsand sensible definition of subtalar joint neutral is the with inverted or everted forefoot positions do notposition in which the subtalar joint is neither pronat- usually corroborate the underlying theory.ed nor supinated, but the validity of this position has Originally Root et al 9 and Sgarlato10 assumed thatnever been established. Many methods have been forefoot varus was due to a lack of normal talar headdeveloped to clinically determine this position,67 torsion. More recent investigators, such as Seibel43such as the now discredited calculation method,47 and Valmassy,42 have been even more assertive inthe palpation of the talar head method, and observa- attributing forefoot varus to this phenomenon despitetion of the lateral skin curves, but none of these evidence to the contrary79 and the lack of evidenceestablishes validity. The ability of clinicians to place that the frontal-plane position of the talar head isthe foot in this position is extremely variable.68, 69 related to the frontal-plane position of the forefoot.80According to Root et al,9 the goal of the orthosis is to In contrast, recent evidence shows that the trans-ensure that the subtalar joint is in its neutral position verse-plane position of the head and neck of the talusat midstance or slightly before heel-off in preparation does influence the forefoot position.81 There is alsoVolume 88 • Number 2 • February 1998 57
  6. 6. no evidence that the posterior bisection of the calca- tored during a clinical trial. Only three studies 87-89neus is perpendicular to the plantar surface of the have prospectively evaluated the use of functionalcalcaneus, which is used as the reference plane for foot orthoses in randomized controlled trials, twofrontal-plane forefoot deformity. Possible distortion with positive outcomes 88, 89 and one with a negativeof the plantar calcaneal fat pad from the bony con- outcome.87 The two positive reports involved adultstour during nonweightbearing could disguise the true with rheumatoid arthritis 88 and diabetes,89 and theplantar rearfoot plane and give the appearance of an negative report concerned healthy children.87 Noneinverted forefoot.80 This soft-tissue distortion raises of them compared the functional foot orthosis withthe question of what exactly is replicated by the sur- another type of device, but instead compared its useface of the neutral position cast.80 It is a common with no intervention,87 a placebo,88 or palliative care.89assumption that the soft-tissue contour of the non- It is unclear whether similar results would have beenweightbearing foot reflects the true osseous position, obtained with a comparison of different types ofwhen in fact there is no evidence to support this. devices. Clearly, there is a relationship between excessive Problems can exist with the clinical application ofsubtalar joint pronation and patellofemoral joint dys- the paradigm, in the form of excessive use or abusefunction,82, 83 but the pathologic mechanisms have not of orthoses by clinicians. The overuse may stem fromyet been elucidated,77, 84, 85 with no or minimal changes a lack of knowledge,90 but there is also an inherentobserved in knee kinematics with orthoses in experi- conflict in prescribing a product (foot orthoses) formental situations. which one gets reimbursed, which is not the case for In a review of the effectiveness of children’s foot other products such as pharmaceuticals. Anotherorthoses in the treatment of pediatric flatfoot, Kirby major problem could be, as Anthony 8(p109) asserts,and Green86 noted that a number of experimental stud- “that control of abnormal compensation that is noties found that foot orthoses reduce not only symp- associated with the patient’s specific problem consti-toms associated with an overpronating foot but also tutes one of the main causes of treatment failurethe magnitude, velocity, and acceleration of rearfoot when using functional orthotic devices as a treatmentpronation. However, a review of the literature by modality.” Common problems 91 include the use ofKilmartin and Wallace 84 led them to the different con- orthoses that are not indicated, errors in the castingclusion that no single piece of research has yet proved technique, inappropriate choice of orthotic materials,the advantage of placing the foot in a supinated or and faulty prescription and manufacture. It is some-neutral position rather than a pronated position. what paradoxical, as noted by Kilmartin and Wal-Sims and Cavanagh85 noted that although studies lace,84 that the two texts 7, 8 on the prescription andhave claimed that foot and ankle symptoms are usu- manufacture of functional foot orthoses imply thatally dramatically decreased with the use of foot incorrectly prescribed orthoses may cause damageorthoses, the objective improvement in rearfootmotion is considerably more modest, suggesting that to the foot of the wearer, yet the authors of these twotherapeutic success is not necessarily due to restor- texts have two different clinical approaches to theing the foot to what is functionally considered “nor- use of the functional foot orthosis.mal.” This raises the possibility that foot orthoses are A large part of the theory of foot function pro-effective for reasons that are not entirely clear. A posed by Root et al 9 is based on a “hinge” model ofnumber of the experimental studies did not use func- the subtalar and midtarsal joints and the two-axestional foot orthoses but rather flexible or semirigid model of the midtarsal joint. However, there are nodevices based on the principles of functional foot true hinge joints in the foot,85, 92 and the two-axesorthoses, which some8 would consider to be flawed. model of the midtarsal joint has been discredited for The lack of prospective, randomized, controlled some time now.85, 93, 94 The talonavicular joint is justtrials comparing functional foot orthoses with other as important as the subtalar joint in translating trans-types of devices is a major criticism directed at the verse rotation of the leg. As positional variation ofparadigm. The difficulty in conducting such studies the subtalar joint axis affects the range of frontal-must be acknowledged: They involve many subject plane movement of the calcaneus with movement ofvariables associated with pathology, countless pre- the subtalar joint, and with this more recent under-scription and manufacturing variables, and difficulty standing of the midtarsal joint, the use of frontal-in defining appropriate endpoints and outcomes that plane movement of the calcaneus for determining theare valid, accurate, and reliable. Also lacking is an effectiveness of an orthosis in clinical and researchobjective measure of orthotic efficacy comparable to settings may not be valid. Confusion also exists as tothe tissue concentration of drugs that can be moni- the stability of the foot when the subtalar joint is58 Journal of the American Podiatric Medical Association
  7. 7. pronated,44, 46 with Root et al 9 suggesting that it is a behind the approach rather than its superficial aspects.less stable position and Sarrafian95 suggesting that it Indeed, a profession’s willingness to subject its ownis a more stable position. procedures and methods to critical self-evaluation can be considered a sign of that profession’s maturity.The Importance of Critical Thinking Future DirectionsHave these “puzzles” or inconsistencies become suf-ficient to precipitate a paradigm shift? Although For a paradigm shift to occur, there must be alterna-these problems have become apparent through tives to the existing paradigm. Classic paradigmattempts to improve the fit between the model and shifts cited by Kuhn include the shift in astronomyreality, they do not rate a mention in recent texts 5, 7, 8, 42, 43 from the Ptolemaic (earth-centered) view to theand appear to be either unknown or largely ignored Copernican (sun-centered) one 48 and the shift fromby those who are most supportive of the paradigm. Aristotelian to Newtonian physics. In all of theseKuhn’s work emphasizes the role of socialization, the cases, a number of anomalies became apparent in theprocess by which young practitioners are educated original paradigm, and then the alternative emerged.or indoctrinated into the current paradigm. Because The paradigm shift requires community agreement,research and practice are conducted within a social not just conversion by individuals. A few alternativescommunity of practitioners, the way in which these are starting to emerge that may affect the clinical prac-communities are organized is of crucial significance tice of podiatric biomechanics as they become morein the production of knowledge. Kuhn’s early work 96 fully developed as coherent theoretical frameworks.explored the role of dogma in scientific research. There are several possibilities for the future courseKuhn considered textbooks of a discipline to be cru- of podiatric biomechanics. The first possibility is thatcial vehicles of socialization into a paradigm. It is no paradigm shift will occur. It is entirely possibleunlikely that Root et al9 considered their text to be that the anomalies discussed above will prove insuf-the final word. The work should have been just a ficient to undermine the fundamentals of the para-starting point; yet the paradigm has been defined by digm. Further theoretical development, experiments,a dogmatic and unquestioning literal interpretation and empirical observations could resolve the anoma-of their text. Popper 97 characterized Kuhn’s normal lies. However, this is increasingly unlikely given thescience as “the activity of the non-revolutionary, or fundamental inconsistencies in the currently prevail-more precisely, the not too critical professional; of ing theory.the . . . student who accepts the ruling dogma of the The second potential direction for podiatric bio-day; who does not want to challenge it . . . all teach- mechanics is the adoption of a paradigm that empha-ing at the University level should be training and sizes the neurophysiologic, neuromechanical, or pro-encouragement in critical thinking . . . the normal sci- prioceptive effects of foot orthoses. Normally theentist, as described by Kuhn has been badly taught. joint, skin, and muscle proprioceptors work togetherHe has been taught in a dogmatic spirit; he is a victim to provide the central nervous system with informa-of indoctrination. He has learned a technique which tion about position and movement. This informationcan be applied without asking for the reason why.” is analyzed against a desired normal pattern to pro- Recently, podiatric education in the United King- duce an appropriate motor response. Abnormaldom, 98 Australia, and New Zealand 99 has gone motion patterns will affect proprioception, and footthrough a transition from a curriculum focusing on orthoses will alter proprioceptive inputs to the cen-technical skills to one that highlights critical think- tral nervous system. To date very little coherent the-ing, with much more emphasis now being placed on ory has been developed in this area. There is a pro-the critical evaluation of fundamental assumptions prioceptive center located in the subtalar joint.100 Itthat underpin podiatric clinical practice. The clinical appears that the interosseous ligament plays anpractice of podiatric biomechanics by podiatrists important role in rearfoot proprioception. Supinationoutside the US takes place in very different health- of the subtalar joint increases afferent feedback to thecare contexts. Podiatrists outside the US have con- central nervous system, while pronation decreases it.siderably less scope in clinical practice, leading to Michaud 5 suggests that by improving the progres-greater reliance on mechanical therapies, the use of sion of forces, the orthosis acts to reeducate the cen-which requires systematic evaluation. The critical tral nervous system as to ideal patterns of muscleevaluation of an approach to patient care is not nec- recruitment. This could be an explanation for theessarily a destructive process; it is best viewed as a phenomenon, anecdotally reported by a number ofmethod of assessment that emphasizes the principles clinicians, of an apparent period of normal foot func-Volume 88 • Number 2 • February 1998 59
  8. 8. tion after removal of an orthosis. It also appears that originally proposed by Root et al11 that classifies feetsubtle intertarsal movements are conducive to nor- on the basis of what causes the abnormal function.mal balance, as those with a tarsal coalition have Under this proposed classification, for example,some trouble balancing on one foot. Stimulation of when the center of pressure is lateral to the subtalarthe cutaneous mechanoreceptors on the plantar sur- joint axis, a pronation moment from the ground isface of the foot also seems to have functional signifi- acting on the foot. There must be an equal and oppo-cance. Stimulation under the metatarsophalangeal site supination moment within the foot counteringjoints has been shown to result in a contraction of the pronation from the ground. This supinationthe digital plantar flexors 101 that redistributes plantar moment could be caused by the osseous end range ofground reactive forces. Stimulation of the skin in the motion, the plantar fascia, or a supinator musclearch (on which any type of foot orthosis will press) such as the posterior tibial muscle. Depending ondorsiflexes the digits, effectively increasing the which structure or structures provide the supinationground reactive forces under the metatarsal heads. moment, various pathologies could result. The ad-This has led to speculation that it is footwear that vantages of this new classification system are that itattenuates plantar sensations that is responsible for is not reliant on the inaccurate measurement tech-pathology.102 Also of interest here is the use of the niques, pathology correlates with physical findings,“dynamic” foot orthosis103, 104 for the treatment of and treatment is aimed at reducing stress on themild-to-moderate spasticity. It uses a sensorimotor anatomic structures involved (E Fuller, DPM, per-approach to control motor output by changing senso- sonal communication, 1997). How this can be trans-ry input, so that unwanted foot movements are con- lated into a system for the prescription of foottrolled by other than purely mechanical means. None orthoses for mechanical foot pathology has not yetof these observations point to any emerging coherent been explored.framework, so further development of them is needed. A fifth option, the tissue-stress model as proposed The sagittal-plane facilitation of motion model105 is by McPoil and Hunt,109, 110 states that there must be aa potential third direction for podiatric biomechan- reduction of tissue stress to tolerable levels (Table 1).ics; it is based on the work of Dananberg.106, 107 In this Placing undue emphasis on the orthosis to themodel, the foot is considered to have three autosup- neglect of other aspects of an optimal managementportive mechanisms: the close packing of the calca-neocuboid joint, the windlass mechanism, and thewedge-and-truss effect. All require the timely andefficient function of the foot in the sagittal plane so itcan resist stress. Any blockage of this sagittal-planemotion, even momentarily, will result in the failure of Table 1. The Tissue-Stress Model109, 110one or all of these mechanisms, leading to the occur- 1. Identify the involved tissues on the basis of symptomsrence of compensation and pathology at other and other subjective information obtained from the history.sites.106, 107 An orthosis is used to reestablish this pre- 2. Apply various stresses to the involved tissues to replicatecise direction of weight flow through the foot so that symptoms through the use of nonweightbearing andthe foot can establish its own autosupportive mecha- weightbearing tests as well as palpation.nisms at the time of heel-off, when power generation 3. Determine whether the patient’s complaint is caused byis at its maximum. It has been suggested105 that this excessive mechanical loading, then ascertain whethermodel is theoretically coherent and biologically plau- the problem is related to:sible as an explanation for the anomalies that have a. excessive foot pronationemerged in the context of the current Root-based b. lack of foot mobilitymodel. This model’s use of in-shoe pressure mea- c. limitation in flexibilitysurement to prescribe orthoses designed to direct d. decreased muscle strengthweight flow through the foot overcomes the above- 4. Follow a management protocol that emphasizes:mentioned problems with static measurements. A potential fourth direction for podiatric biome- a. reducing tissue stress to a tolerable level through rest, activity modification, footwear, and/or orthoseschanics has been indicated by Fuller,108 who has pro-posed a classification system that is an extension of b. healing the involved tissues through medication and physical therapythe work by Kirby 32, 33 on rotational equilibrium aboutthe subtalar joint. Fuller’s system classifies feet by c. the restoration of lower-extremity flexibility and muscle strengthlooking at stress in anatomic structures rather thanabnormal position. This contrasts with the system d. a plan for the gradual resumption of daily activities60 Journal of the American Podiatric Medical Association
  9. 9. plan is a problem with the clinical application of the Acknowledgment. Eric Fuller, Kevin Kirby,current paradigm, as stated above. The tissue-stress Anne-Maree Keenan, Hylton Menz, and Trevor Priormodel is a useful starting point for the development for comments on earlier versions of this essay.of optimal intervention strategies, regardless of thetype of orthosis used. References Another possibility is the emergence of an as-yet-unknown new paradigm. 1. R OOT ML: “Foreword,” in Clinical Biomechanics of the Lower Extremities, ed by RL Valmassy, p vii, CV All of these conceptual frameworks require fur- Mosby, St Louis, 1996.ther work, but most are sufficiently developed that 2. Dorland’s Illustrated Medical Dictionary, 28th Ed,they can begin to inform clinical practice. It remains WB Saunders, Philadelphia, be seen which direction will be the most success- 3. K IRBY K: Podiatric biomechanics: an integral part offul in this regard, as there is no rational mechanism evaluating and treating the athlete. Med Exerc Nutr Health 2: 196, 1993.for evaluating one paradigm in terms of another par- 4. H UNT GC, M C P OIL TG ( ED ): Physical Therapy of theadigm. It is possible for more than one paradigm to Foot and Ankle, 2nd Ed, Churchill Livingstone, Newexist simultaneously, in a manner similar to the way York, 1995.that the psychosocial model of health sits beside the 5. MICHAUD TC: Foot Orthoses and Other Forms of Con-biomedical model. There will always be attempts to servative Foot Care, Williams & Wilkins, Baltimore,integrate paradigms with each other as a means of 1993. 6. CHAO EYS: Orthopaedic biomechanics: the past, pres-saving a given paradigm. This is generally done by ent and future. Int Orthop 20: 239, 1996.those who are still “wearing the lens” of the current 7. P HILPS JW: The Functional Foot Orthosis, Churchillparadigm and could be considered an attempt to co-opt Livingstone, New York, 1990.the competing paradigm. For example, it has been 8. A NTHONY RJ: The Manufacture and Use of the Func-alleged111 that the biopsychosocial model of health is tional Foot Orthosis, Karger, Basel, 1991. 9. ROOT ML, ORIEN WP, WEED JH: Normal and Abnormalnothing more than an attempted takeover of the Function of the Foot, Clinical Biomechanics Corp, Lospsychosocial model by the biomedical model. The bio- Angeles, 1977.medical model has the support of powerful financial 10. SGARLATO TE: A Compendium of Podiatric Biomech-interests, namely, the pharmaceutical industry.112 anics, California College of Podiatric Medicine, SanSimilarly, the current podiatric biomechanics para- Francisco, 1971. 11. ROOT ML, ORIEN WP, WEED JH: Biomechanical Exam-digm is supported by the commercial orthotic indus- ination of the Foot, Clinical Biomechanics Corp, Lostry, which will resist any paradigm shift that it does Angeles, 1971.not regard as in its own interest. 12. ROOT ML, WEED JH, ORIEN WP: Neutral Position Cast- ing Techniques, Clinical Biomechanics Corp, LosConclusion Angeles, 1971. 13. ANTHONY RJ: Treating the runner. Chiropodist 37: 228, 1982.This analysis has reviewed the history and develop- 14. A RCHIBALD N: Australian podiatry of the future. Austment of the field of podiatric biomechanics, as well Podiatr 15: 6, current thinking about its underpinnings and future, 15. P AYNE CB: Biomechanics of the Foot and Relatedin the context of a theoretical framework drawn from Pathology, Podiatry Associates, Riccarton, New Zea-the philosophy and sociology of science. This analysis land, 1982.has been used to explore possible future directions 16. 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WHITMAN R: Observations on seventy-five cases of flatcritically on what has been written as well as on per- foot. Trans Am Orthop Assoc 1: 1888.sonal experience, practitioners will come to a fuller 22. ROBERTS PW: The influence of the oscalcis on the pro- duction and correction of valgus deformities of theunderstanding of their own methods and views. foot. Am J Orthop Surg 14: 1916.Paradigms call for critical engagement, not dogmatic 23. M ORTON DJ: The Human Foot, Columbia Universityadherence. Press, New York, 1942.Volume 88 • Number 2 • February 1998 61
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