1. The Past, Present, and Future of
Podiatric 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 the
context of a theoretical framework drawn from the philosophy and soci-
ology of science. This analysis sets the stage for an exploration of the
possible 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 interactions
chanics, it is necessary to understand the past. The of the foot with the lower extremity.3 However, the
philosophy, 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 medical
practice and serve as guides to the future. The pur- practice. Its principles have been widely adopted in
pose 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 outside
chanics 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 orthopedic
time for changes to occur in the clinical practice of biomechanics is considered a part.6
podiatric 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 of
podiatric 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 and
for 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 the
The 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 and
atrist with an invaluable diagnostic ability that can- neutral-position casting methods.12 After gaining
not be otherwise matched.”1 The term “biomechan- wide acceptance in clinical practice in the US, the
ics” 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 into
chanics 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 of
Bundoora, Victoria 3083, Australia. foot biomechanics to guide therapy. Early contribu-
Volume 88 • Number 2 • February 1998 53

2. tions to the literature18 include a description in 1845 its wide acceptance and is based on deviations from
by 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 they
scribed the use of additions to the outer sole of the defined it was considered to cause abnormal foot
shoe to treat foot disorders. A different approach function, resulting in a particular set of signs and
was 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 a
that was designed to press on the navicular, causing cast 8, 12, 30 is made of the foot in its neutral position to
the foot to invert by force or from muscular contrac- capture these deviations in alignment. A functional
tion due to pain. Roberts 22 in 1916 developed a metal foot orthosis7, 8, 17 is then constructed, with posts
brace 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, thereby
Morton23 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 theory
lengthen the first ray. Early contributions from podia- have seen a number of developments, including the
try include that of Schuster,24 who in the 1920s devel- use of extrinsic forefoot posting, 8 application of
oped what became known as the Roberts-Whitman direct pressure on the fourth and fifth metatarsal
brace, 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 in
quired 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, 38
Levy mold; it had a thick leather cover, with the sup- the DC (direct control) inverted wedge,39 the use of
port made of a latex compound. Root later used and scanners 40 to replace the plaster casting process, and
modified 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, 41
static structure, with the height of the arch consid- The widespread application of the principles of
ered paramount. More detailed descriptive accounts podiatric biomechanics in clinical practice has not
of the historical development of mechanical foot been accompanied by an abundance of published
therapy 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 most
pline without recognizing the broader context, the recently published textbooks 5, 7, 8, 42, 43 as well as the
factors 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 reflects
ry podiatric orthopedics began to develop its own the clinical experience of talented practitioners and
unique 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 views
work, which had a dramatic impact on the clinical are greeted with antagonism 44 and a confusion of fact
practice of podiatric medicine. They brought togeth- with theory. Strongly promulgated postulates tend to
er 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 more
forefoot-rearfoot relationship when the midtarsal systematically and objectively evaluated, and postu-
joint is “locked,” while introducing a theoretical lates and assumptions that have become entrenched
coherence 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 Science
orders constituted a dramatic shift in the understand-
ing of the foot and its mechanical relationship to the The philosophy of science is concerned with the
rest of the kinetic chain, emphasizing the foot as a nature and foundations of what is considered to be
dynamic rather than a static structure. Their theoreti- scientific knowledge, while the sociology of science
cal framework has remained largely unchanged since concerns the social processes involved in the pro-
54 Journal of the American Podiatric Medical Association

3. duction of this scientific knowledge. Many philoso- “paradigms” are overthrown and replaced by other
phers 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 periods
sion 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 intellectual
sion 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 period
phy 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 assumptions
process 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 direct
empirically.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 the
knowledge 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 podiatric
examined in more and more detail, increasingly accu- biomechanics: It can help explain the field’s past as
rate observations are made, and increasingly sophis- well as help predict its future.
ticated experiments and observations are carried
out. In this way, new concepts and theories to explain A Paradigm in Podiatric Biomechanics
reality evolve, and knowledge grows. The history of a
particular scientific discipline is seen as a linear devel- A paradigm is difficult to define precisely, but it
opment toward scientific truth by means of steadily includes scientific laws and theoretical assumptions
improving scientific methods. In this view, science is as well as how they are applied. Kuhn characterized
fundamentally evolutionary and progressivist. paradigms as “universally recognized achievements,
The descriptive accounts of the history of podi- that for a long time provide model problems and
atric biomechanics by Schuster18 and Levitz et al27 solutions to a community of practitioners.”51(p176) The
illustrate 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 scientific
cessor of the forefoot posting developed by Root. thinking and action. Paradigms structure scientific
Yet, although Root et al 9 cite Schreiber and Weiner- observation in particular ways: Observations are
man’s work, there is no evidence that they were made in light of the concepts and theories that are
influenced 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 paradigm
ever, 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 paradigm
the two. Also, while Anthony 8 refers to the influence typically starts with attempts to resolve a particular
of the Levy mold on Root’s development of the func- range of problems or develop a body of theoretical
tional orthosis, the functional foot orthosis actually knowledge about some aspect of the world. In this
bears 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 coherent
major branches of science does not exhibit the struc- model or methodology. Kuhn cites as an example the
ture assumed by the positivist approach. Kuhn51, 52 wide diversity of theories in optics before Newton
interpreted 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 before
Volume 88 • Number 2 • February 1998 55

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 the
in 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 the
the 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 existing
operate and in terms of which a particular interpreta- paradigm, marking the end of the period of “normal
tion of “reality” is generated, so that any new theo- science.” According to Kuhn, the anomalies that pose
ries generated will be consistent with the view of problems for the paradigm result in “pronounced
reality 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 are
community. 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 existing
usually takes the form of “puzzle-solving,” with the paradigm is abandoned and a new paradigm that has
puzzles always defined by and soluble in terms of the gained the allegiance and support of researchers and
dominant paradigm. This period of normal science is practitioners takes its place. This process of “paradigm
characterized 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 a
paradigm and reality, but the fundamentals of the “revolution” brought about by the “conversion” of the
paradigm are not questioned. The pre-scientific peri- community. This abandonment of one theoretical
od in the field of podiatric biomechanics essentially structure and its replacement by another one that is
came to an end with the work of Root and his col- incompatible with the first is a key point in Kuhn’s
leagues, which was widely accepted by the podiatric structure of scientific revolutions. The new paradigm
community as a unifying framework or paradigm then guides normal scientific activity until sufficient
that 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 of
to 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 paradigm
biomechanics 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 evaluated
digm applies primarily to podiatric management of only with difficulty. Proponents of one paradigm or
the 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 two
The paradigm did not gain wide acceptance in the groups tend to talk past each other. The observations
orthopedic profession for management of the foot; or conclusions drawn by the proponents of a given
indeed, it has been described by members of that paradigm reflect the beliefs, values, and interests of
community 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 came
ing foot mechanics.62 from practitioners who tried to relate what he was
saying to what they already knew. The problem many
The Process of Paradigm Shift people have in understanding new paradigms is not
necessarily due to any difficulty inherent in the new
The activities that take place during the period of paradigm, but rather relates to the fact that the new
normal science continue as long as the paradigm sat- paradigm is being viewed through the “lens” of the
isfactorily 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 West
explain everything. In attempting to discover solu- Coast of the US that occurred in the understanding
tions to puzzles, researchers will eventually run into of Root’s original work. Similarities can be seen in
difficulties. Puzzles that resist solution are seen with- Constant’s 63 account of the development of the jet
in 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 piston
56 Journal of the American Podiatric Medical Association

5. engine paradigm and were reluctant to take seriously for the propulsive phase of gait. In support of this
any 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 Root
Although there has always been a certain amount of et al would consider the relaxed calcaneal stance
resistance to the theories originally proposed by position. Two more recent reports confirmed that
Root, 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, 72
it was incorporated into clinical practice. With time, Several studies, reviewed by Menz,73 examined the
however, the number of anomalies or puzzles within reliability of measurement procedures that were
the current podiatric biomechanics paradigm has originally described by Root et al,11 with most finding
become apparent as attempts have been made to intratester reliability to be reasonably good but
improve 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 during
really an anomaly in Kuhnian terms but has led to assessment of patients and for prescription of
difficulty in understanding of the paradigm. The use orthoses. Three studies74-76 have concluded that static
and intended meaning of certain terms, which were measurements are not good predictors of dynamic
originally elucidated very clearly by Root et al,11 have limb function. The use of medial foot wedges was
given rise to different interpretations and disagree- found to significantly reduce the “Q angle” during
ment 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 plaster
in 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 a
nition than the podiatric one. Indeed, the criteria of statistically significant difference between the static
Root et al might allow the entire population to be and dynamic arch index values, suggesting that the
classified as “abnormal.”45, 46 Reference ranges are traditional method of static casting may not result in
widely used in medicine to determine normality; thus an adequate representation of a dynamic foot. The
it would be expected that the criteria originally pro- assessment of the range of motion of the subtalar
posed by Root et al for normalcy would fall in the joint is done in a nonweightbearing position, but
middle of a normal bell-shaped distribution in a pop- there is a difference between the weightbearing and
ulation 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 this
sider the criteria for the normal or ideal foot as joint.78 Many clinicians who are familiar with in-shoe
defined by Root et al to be based on an invalid theo- plantar pressure measurements anecdotally report
retical 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 patients
and sensible definition of subtalar joint neutral is the with inverted or everted forefoot positions do not
position 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 that
never been established. Many methods have been forefoot varus was due to a lack of normal talar head
developed to clinically determine this position,67 torsion. More recent investigators, such as Seibel43
such as the now discredited calculation method,47 and Valmassy,42 have been even more assertive in
the palpation of the talar head method, and observa- attributing forefoot varus to this phenomenon despite
tion of the lateral skin curves, but none of these evidence to the contrary79 and the lack of evidence
establishes validity. The ability of clinicians to place that the frontal-plane position of the talar head is
the foot in this position is extremely variable.68, 69 related to the frontal-plane position of the forefoot.80
According 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 talus
at midstance or slightly before heel-off in preparation does influence the forefoot position.81 There is also
Volume 88 • Number 2 • February 1998 57

6. no evidence that the posterior bisection of the calca- tored during a clinical trial. Only three studies 87-89
neus is perpendicular to the plantar surface of the have prospectively evaluated the use of functional
calcaneus, which is used as the reference plane for foot orthoses in randomized controlled trials, two
frontal-plane forefoot deformity. Possible distortion with positive outcomes 88, 89 and one with a negative
of the plantar calcaneal fat pad from the bony con- outcome.87 The two positive reports involved adults
tour during nonweightbearing could disguise the true with rheumatoid arthritis 88 and diabetes,89 and the
plantar rearfoot plane and give the appearance of an negative report concerned healthy children.87 None
inverted forefoot.80 This soft-tissue distortion raises of them compared the functional foot orthosis with
the question of what exactly is replicated by the sur- another type of device, but instead compared its use
face of the neutral position cast.80 It is a common with no intervention,87 a placebo,88 or palliative care.89
assumption that the soft-tissue contour of the non- It is unclear whether similar results would have been
weightbearing foot reflects the true osseous position, obtained with a comparison of different types of
when in fact there is no evidence to support this. devices.
Clearly, there is a relationship between excessive Problems can exist with the clinical application of
subtalar joint pronation and patellofemoral joint dys- the paradigm, in the form of excessive use or abuse
function,82, 83 but the pathologic mechanisms have not of orthoses by clinicians. The overuse may stem from
yet been elucidated,77, 84, 85 with no or minimal changes a lack of knowledge,90 but there is also an inherent
observed in knee kinematics with orthoses in experi- conflict in prescribing a product (foot orthoses) for
mental 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. Another
orthoses 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 not
ies 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 failure
the magnitude, velocity, and acceleration of rearfoot
when using functional orthotic devices as a treatment
pronation. However, a review of the literature by
modality.” Common problems 91 include the use of
Kilmartin and Wallace 84 led them to the different con-
orthoses that are not indicated, errors in the casting
clusion 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 and
have claimed that foot and ankle symptoms are usu-
manufacture of functional foot orthoses imply that
ally dramatically decreased with the use of foot
incorrectly prescribed orthoses may cause damage
orthoses, the objective improvement in rearfoot
motion is considerably more modest, suggesting that to the foot of the wearer, yet the authors of these two
therapeutic success is not necessarily due to restor- texts have two different clinical approaches to the
ing 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 of
number of the experimental studies did not use func- the subtalar and midtarsal joints and the two-axes
tional foot orthoses but rather flexible or semirigid model of the midtarsal joint. However, there are no
devices based on the principles of functional foot true hinge joints in the foot,85, 92 and the two-axes
orthoses, 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 just
trials 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 of
paradigm. 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 of
variables 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 the
are valid, accurate, and reliable. Also lacking is an effectiveness of an orthosis in clinical and research
objective measure of orthotic efficacy comparable to settings may not be valid. Confusion also exists as to
the tissue concentration of drugs that can be moni- the stability of the foot when the subtalar joint is
58 Journal of the American Podiatric Medical Association

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 own
is 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 Directions
Have 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 paradigm
attempts to improve the fit between the model and shifts cited by Kuhn include the shift in astronomy
reality, they do not rate a mention in recent texts 5, 7, 8, 42, 43 from the Ptolemaic (earth-centered) view to the
and appear to be either unknown or largely ignored Copernican (sun-centered) one 48 and the shift from
by those who are most supportive of the paradigm. Aristotelian to Newtonian physics. In all of these
Kuhn’s work emphasizes the role of socialization, the cases, a number of anomalies became apparent in the
process 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 alternatives
community 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 more
in 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 course
Kuhn considered textbooks of a discipline to be cru- of podiatric biomechanics. The first possibility is that
cial vehicles of socialization into a paradigm. It is no paradigm shift will occur. It is entirely possible
unlikely 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 the
science 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 the
entist, as described by Kuhn has been badly taught. joint, skin, and muscle proprioceptors work together
He 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 information
can 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. Abnormal
dom, 98 Australia, and New Zealand 99 has gone motion patterns will affect proprioception, and foot
through 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 It
that underpin podiatric clinical practice. The clinical appears that the interosseous ligament plays an
practice of podiatric biomechanics by podiatrists important role in rearfoot proprioception. Supination
outside the US takes place in very different health- of the subtalar joint increases afferent feedback to the
care 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 muscle
evaluation of an approach to patient care is not nec- recruitment. This could be an explanation for the
essarily a destructive process; it is best viewed as a phenomenon, anecdotally reported by a number of
method of assessment that emphasizes the principles clinicians, of an apparent period of normal foot func-
Volume 88 • Number 2 • February 1998 59

8. tion after removal of an orthosis. It also appears that originally proposed by Root et al11 that classifies feet
subtle 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 subtalar
the cutaneous mechanoreceptors on the plantar sur- joint axis, a pronation moment from the ground is
face 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 countering
joints has been shown to result in a contraction of the pronation from the ground. This supination
the digital plantar flexors 101 that redistributes plantar moment could be caused by the osseous end range of
ground reactive forces. Stimulation of the skin in the motion, the plantar fascia, or a supinator muscle
arch (on which any type of foot orthosis will press) such as the posterior tibial muscle. Depending on
dorsiflexes the digits, effectively increasing the which structure or structures provide the supination
ground 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 it
attenuates 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 the
mild-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 foot
trolled by other than purely mechanical means. None orthoses for mechanical foot pathology has not yet
of 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 a
a 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 the
model, the foot is considered to have three autosup- neglect of other aspects of an optimal management
portive mechanisms: the close packing of the calca-
neocuboid joint, the windlass mechanism, and the
wedge-and-truss effect. All require the timely and
efficient function of the foot in the sagittal plane so it
can resist stress. Any blockage of this sagittal-plane
motion, even momentarily, will result in the failure of Table 1. The Tissue-Stress Model109, 110
one or all of these mechanisms, leading to the occur- 1. Identify the involved tissues on the basis of symptoms
rence 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 replicate
cise direction of weight flow through the foot so that symptoms through the use of nonweightbearing and
the 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 by
is at its maximum. It has been suggested105 that this excessive mechanical loading, then ascertain whether
model is theoretically coherent and biologically plau- the problem is related to:
sible as an explanation for the anomalies that have a. excessive foot pronation
emerged in the context of the current Root-based b. lack of foot mobility
model. This model’s use of in-shoe pressure mea- c. limitation in flexibility
surement to prescribe orthoses designed to direct d. decreased muscle strength
weight 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 orthoses
chanics 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 therapy
the work by Kirby 32, 33 on rotational equilibrium about
the subtalar joint. Fuller’s system classifies feet by c. the restoration of lower-extremity flexibility and muscle
strength
looking at stress in anatomic structures rather than
abnormal position. This contrasts with the system d. a plan for the gradual resumption of daily activities
60 Journal of the American Podiatric Medical Association

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 Prior
model is a useful starting point for the development for comments on earlier versions of this essay.
of optimal intervention strategies, regardless of the
type of orthosis used. References
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