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In Memoriam

Childress, Dudley S. PhD

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Journal of Prosthetics and Orthotics: October 2014 - Volume 26 - Issue 4 - p 172-176
doi: 10.1097/JPO.0000000000000045
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For four decades, Dr. Dudley Childress was a key figure in rehabilitation engineering and internationally recognized as a leader in the field of prosthetics and orthotics research. His achievements in the field of rehabilitation research were acknowledged through numerous awards and honors. Dr. Childress mentored approximately 50 graduate students at the MS and PhD levels during his career. Many of his former students are now working as prosthetists and orthotists, rehabilitation research engineers, managers of gait analysis laboratories, physicians, orthopedic surgeons, and professors at major universities with their own research programs. Through the careful, patient nurturing and attention invested in his students, Dr. Childress created a far-reaching and perpetual influence on the field of rehabilitation engineering research, particularly in the area of prosthetics and orthotics. After a long illness, Dr. Childress passed away on August 6, 2014. —Steven A. Gard, PhD, Editor-in-Chief

Dudley S. Childress, PhD

Editorial [Reprinted with permission from the Journal of Prosthetics and Orthotics 2002;14: 97]

If asked what scientific, medical, or engineering fields relate to limb prosthetics and orthotics, one might suggest, anatomy, neurophysiology, motor control, electrophysiology, kinesiology, biomechanics, cybernetics, robotics, ergonomics, materials science, machine design, structural design, electronic design, instrumentation, psychology, childhood development, gerontology–the list could go on and on. It has been said that if something contains humans it contains almost everything. Hence, we might say that since prosthetics and orthotics involve humans, these fields involve almost everything. This condition is what makes them so interesting–and so difficult. However, just because many scientific and related disciplines are applicable to a field doesn’t make the field itself scientific. In fact, I believe prosthetics and orthotics generally have low scientific content. At best they seem to have only an immature science associated with them. This is not negative. In fact, it is positive for us working in the field. It means there are many opportunities in the field. Not many people are privileged to be present during a field’s pre-scientific development, during the time when its scientific borders are being opened.

That prosthetics and orthotics are not very scientific is an indication that they are young and developing fields. All fields begin with little or no science. Physics came, to some extent, from metaphysics. Chemistry from alchemy.Most fields are based on a foundation of knowledge that originated empirically; that is, from practical experience and experiment rather than from theory. A knowledge base usually accrues before a science (theory, etc.) can emerge from it. Some fields remain basically empirical. Surgery has been an example of a highly empirical field, but that is changing. Prosthetics and orthotics will probably always have a strong empirical component. Most fields develop into a healthy mixture of science and empiricism, which complement and support each other. It is to be hoped that science will soon begin to have a stronger presence in prosthetics and orthotics. This does not mean that science has not previously been applied to the fields of prosthetics and orthotics; it has, but these applications seem to have come mainly through other more developed fields (e.g., physics, engineering, etc.), as will be discussed later in more detail. What is contended here is that prosthetics and orthotics do not now have much of a science of their own. It is also suggested that science, which can provide a kind of theoretical framework, would be useful to these fields. We currently lack a broad theoretical framework to guide our thinking and interpretations. Science in prosthetics and orthotics could develop the theoretical framework within which these fields could develop in a more orderly and more accelerated fashion.


What is science? This seems an appropriate question; if, as contended in the introduction, a science of prosthetics and orthotics needs to develop. There is no single definition. We know that science is concerned with facts held together by principles (e.g., laws, theories). We know it involves events that can be repeated and that can be measured (quantified). Lord Kelvin said, “If you can’t measure something in numbers, your knowledge of it is not really scientific.” Besides numbers, science frequently involves mathematically-based theory. Einstein said, “The object of all science, whether natural science or psychology is to coordinate our experiences and to bring them into a logical system.” The philosopher of science, Thomas Kuhn (1970), said that normal science is problem solving within a paradigm (examples of paradigms in science are presented later). He claimed a problem solver (a scientist) needs an agreed upon paradigm in order to carry on science. According to Kuhn, fact-finding is more or less a random activity if it is carried out in the absence of a paradigm. A paradigm permits selection, criticism, and evaluation. From a different viewpoint, Karl Popper (1965) emphasized that an important aspect of science is falsification. The contention is that we advance through multiple hypotheses that are systematically reduced in number by demonstration that some are false. We know that negative results are useful in science and engineering as well as in empirical activities.

Progress in science has had many commentators, particularly philosophers of science, but also scientist themselves. Max Planck reportedly said that science progresses one funeral at a time, which suggests the conservative nature of scientists and their reticence to change their ideas. Paul Dirac thought that truth was recognized in science through beauty (elegance). Popper, as already mentioned, thought progress came through falsification. Kuhn thought progress came about through work under paradigms and through paradigm shifts. Peter L. Galison (1997), a historian of science at Harvard, sees modern growth of science (especially physics) as relying upon ever larger and more complex technical apparatus. Many scientists worry about this development but others see complex new tools as becoming more important than new ideas or philosophical arguments. Personally, for prosthetics and orthotics, I like A.V. Hill’s viewpoint, made in 1951, “Progress of knowledge is achieved by trial and error, by experiment and theory acting and reacting on one another. The vital thing is that the error should be confined to the theory and should not be allowed by carelessness or credulity to creep into the experiments.” Nevertheless, new tools such as the modern motion analysis systems are beginning to have a strong impact on prosthetics and orthotics science.

Summarizing, we might say that science has to do with knowledge and facts that are verifiable and quantifiable, that are organized by principles, theories, and laws under some accepted paradigm that enable valid and objective discriminations and comparisons to be made. Science advances by empiricism and theory, by hypotheses and experimentation, by falsification, by instruments and from time to time by paradigm shifts.

Engineering is often regarded as the practical application of science to problems of a field but the boundaries between science and engineering are not distinct. We use terms such as Engineering Science, Rehabilitation Science, Computer and Computational Science, etc. Sydney Harris, the late Chicago newspaper columnist, used to say that if you have to put science in the name there may not be much science in the topic.



The origins of prostheses and orthoses are lost in antiquity. Drawings that show crutches and prostheses exist from Egyptian and Roman cultures. Artisans of the renaissance, such as armorers, devised some remarkable prostheses almost 500 years ago. Wars, particularly the Napoleonic battles in Europe and the Civil War in the United States produced many amputees during the 19th century and a certain maturity in prosthesis making was achieved at that time. The Anglesea Leg, an above-knee prosthesis, used by the Marquis of Anglesea (Wellington’s Cavalry Officer at Waterloo) was developed in the early 1800s and is still in limited use today–a testimony to its longevity and a tribute to the design. The prosthetics firms of J.E. Hanger and of A.A. Marks exemplified the expansion of prosthetics facilities in the United States after the Civil War.

The First World War marked, I believe, the first formal application of science to prosthetics and orthotics. This was mainly the use of science through engineering activities, typified by the work of Professor G. Schlesinger in Berlin. The formal work in Germany led to the publication, Ersatzglieder und Arbeitshilfen (1919). This publication, concerning “replacement limbs and work aids” is a classic summary of the state-of-the-art of prosthetics and orthotics practice early in this century. It remains, even today, a valuable resource for practitioners and researchers alike in prosthetics and orthotics. I believe the attention Germany gave prosthetics and orthotics in the early part of this century, along with its apprenticeship programs, accounts importantly for the high standing Germany has enjoyed through the years in prosthetics and orthotics. Britain established their prosthetics center at Roehampton during this period. By contrast, these fields were not emphasized much in the United States after WWI, although the government did recognize the importance of prosthetics by arranging contracts with private manufacturers and this action was connected with efforts to insure ethical approaches within the industry. This led to the formation in 1917 of The Association of Limb Manufacturers of America, now the American Orthotic and Prosthetic Association. However, no research and development work was fostered. Consequently, at the end of World War II in 1945, the state of prosthetics in the USA was little different from what it had been in the 1920s.

The power that research and development (R&D) funding can have on fields was abundantly demonstrated in the United States during the second world war. Many believe, for example, that those R&D activities changed engineering in the USA from an “art” to a “science.” Consequently, it was natural for the government to feel that R&D in prosthetics would be able to advance this field. In January of 1945, the Surgeon General convened a meeting in Chicago, on the south campus of Northwestern University, to determine what should be done about prostheses for the veterans of the war. This marked the beginning, in the United States, of the application of science to prosthetics, and of course ultimately to orthotics. The meeting symbolized the realization that support of R&D effort was needed if progress was to be made in prosthetics. As we shall see, the subsequent R&D paid off. Practice today in the USA is largely based on the research and development work that was funded following that meeting. Essentially all of the current research funding for prosthetics and orthotics by governmental agencies can in some way be traced to that event in 1945. Paul Klopsteg, an engineer and Director of Research at the Technological Institute of Northwestern University, and Philip Wilson, an orthopaedic surgeon from New York City, were at that first meeting in Chicago in 1945. They subsequently edited Human Limbs and Their Substitutes in 1954, another classic publication of the field. One cannot avoid noticing the similarities between this book and Ersatzglieder und Arbeitshilfen (1919).


The 20-year period after 1945 was an unparalleled period for advances in prosthetics and orthotics, technically and scientifically. Taylor and associates (1955), at UCLA, conducted fundamental studies of the hand and arm that led to substantially improved prosthetic fitting methods and components for the upper arm. Inman and associates (1981) at the University of California (San Francisco and Berkeley) conducted fundamental studies of human walking, the results of which still constitute the “bible” for practitioners around the world. Eberhart, Radcliffe, Foort, and others, also at UCB, developed the concepts of the PTB Socket, the SACH foot, and the quadrilateral socket, all of which are still used today, even though they are challenged by a number of new approaches. Also out of the UCB research came Radcliffe’s biomechanical studies (1955, 1957, 1961, and 1962), which remain standards in the field, even though they probably need to be upgraded. During this time Hans Mauch developed advanced hydraulic knee components and researchers in Canada (McLaurin and Hampton) developed the Canadian hip disarticulation prosthesis. Studies by Jacqueline Perry and others advanced understanding of pathokinesiology and of orthotic principles.

There were, of course, many other contributors during this period, in the USA and internationally. However, I think this brief overview of R&D results demonstrates how change can be influenced by research and development funding. The rapid progress of this period was due to several things,1 the relatively primitive nature of prosthetics and orthotics previous to that time,2 the “can do” approach that was typical of investigators during the post-war period,3 the commitment of funds to R&D by governmental agencies, and4 the effective coordination of research efforts and evaluation projects brought about by the Committee on Prosthetics Research and Development (CPRD) of the National Academy of Sciences/National Research Council (NAS/NRC), led by A. Bennett Wilson, Jr. and Hector W. Kay.

ADVANCEMENTS (1965–1992)

By 1965, or thereabouts, many of the fundamental principles currently used in prosthetics and orthotics had been established. Advancements since then seem to have emphasized technical developments, with less concentration on principles than during the previous 20-year period. Of course, this is only one viewpoint; but, science and technology generally do not advance in a linear fashion at all times. Significant progress from 1965 to 1992 was made in education, materials, and mechanisms. The introduction of new materials (thermoplastics, composites, etc.) and new modular components have greatly altered fabrication techniques. Similarly, new socket design techniques along with more flexible sockets and new suspension methods have improved fitting procedures and given prosthesis/orthosis users more comfort and control. Commercial availability of electric powered arm components and myoelectric control have significantly enhanced artificial arm fitting options, providing many new approaches that complement the older techniques. New “dynamic feet” designs and new knee mechanisms have added significantly to the armamentarium of components for artificial legs. Finally, computer-aided-design and computer-aided-manufacturing (CAD/CAM) of prostheses and orthoses, introduced through research projects in the U.K., Canada, and the U.S., has made computerized techniques of increasing influence on prosthetics and orthotics technology and practice.


Prosthetics and Orthotics are currently in a relatively high state of development. However, in spite of the significant advancements made since 1945, nagging questions about these fields remain. Thoughtful practitioners believe there is much yet to be done. During the period from 1992 to 2002 it has been observed that a number of practitioners and students now not only want to know how to make and/or apply prostheses or orthoses in certain ways, but why they should be made or applied in these ways. There is a desire to have logical and verifiable reasons for using one kind of technical component rather than another. There is a desire to be more discerning with prescription choices; to be able to choose between the good, the better, and the best through more objective judgments than are presently available. Likewise, there is the desire to have understanding that is of greater depth than is currently available. Practitioners today hope for documented scientific-based prescription rationales. In other words, I think there is a increasing desire for more science in orthotics and prosthetics.


The fields of orthotics and prosthetics today are similar to many other areas of rehabilitation. They lack a scientific basis for much of what is practiced. This makes practitioners in these fields not unlike the cathedral builders of the twelfth and thirteenth centuries. The master masons and their assistants were able to construct beautiful cathedrals–great works of art–but if they designed a new structure, they couldn’t be sure if it would stand or not. The cathedral in Siena, Italy is an example. When the builders tried to build a new and much larger nave, with the older nave as the new transept, they were unable to accomplish their task. This was, at least partly, because they had no structural science on which to make their building decisions. Builders today still learn from experience but because of science and engineering modern structures do not have to be built in order to find out if they are going to be safe and effective. Science and engineering should be able to do similar things in prosthetics and orthotics.

Another analogy can be made with the aircraft industry. The Wright brothers were able to build their first airplane largely from empirical knowledge. Many aircraft designs followed that were designed by the “seat of the pants.” It was not until aerodynamic theory, jet turbine theory, hydraulic control theory, electromagnetic radiation theory, and other theories were well developed and well advanced that we were able to fly across the Atlantic at supersonic speeds. Multiple theories, applied to various aircraft systems, have been able to have a profound influence on aircraft design. Again, empiricism and creative intuition still enter in, but there is little guess work associated with modern airplane design.


My contention is that science is needed in prosthetics and orthotics if these fields to advance as rapidly and as orderly as they should. Kuhn (1970) would say that an accepted paradigm needs to develop in order for science to actually be practiced in these fields. Two examples of paradigms in science follow. I do not believe we can currently identify an accepted paradigm in prosthetics or orthotics. This is not to say we should look for one. An accepted paradigm should naturally evolve.

One example of a readily understood paradigm in science can be seen in the field of Geology. Since the 1960s, the field has been operating under what could be called the “plate-tectonic” paradigm. It may be a bit difficult for the external viewer to realize that it is only in the last generation that our understanding of geological processes has been based on the ideas of plate tectonics. Before plate tectonics there was the “geosyncline paradigm,” a paradigm most of us would not recognize or understand. This situation does not mean that concepts related to plate tectonics did not exist before the 1960s. Continental drift was proposed as early as 1920 and Francis Bacon had noticed in the 1600s that the continents of Africa and South America more or less fit together like pieces of a puzzle. Nevertheless, scientists before the 1960s did not use plate tectonics as a paradigm to guide their work. Today, virtually all scientists in geology work under this paradigm.

The field of astronomy is fertile for paradigms and instructive with respect to the development of science. When the paradigm had the earth at the center of the cosmos it ultimately became increasingly difficult for observers to match planet positions with predicted locations. Copernicus suggested a new paradigm (The Greeks had this notion much earlier) with a sun-centered system and this was eventually accepted. Still, it remained for Kepler to accurately describe planetary motion and he could not have done it without Tycho Brahe’s observations (data). King Frederick of Denmark gave Brahe one of the first government grants and Brahe demonstrated what funding can do. He also demonstrated the importance of excellent instrumentation and accurate measurements in science. As an aside, it is interesting to note, particularly for people in prosthetics, that Brahe had a prosthetic nose made of gold and silver.

Brahe’s experimental data led to Kepler’s mathematical descriptions of planetary motion–and what Kepler thought was understanding of the music of the spheres. These results were the foundation upon which Newton developed the theory of gravity, which for most practical purposes explains and predicts motion in the heavens. Of course, it was Newton’s new paradigm that has allowed us to transport men to the moon, to place instruments on Mars, and to fly instruments near or into other planets. Theories are not just intellectual tinsel, they often produce results of the most practical sort! This is why I believe the development of a theoretical component is so important to prosthetics and orthotics. It is the natural progression for fields like P&O, where empiricism is strong.


I might point out that I view motion analysis data as being similar to the observational data of the planets some 500 years ago. Much data was collected by many observers with varying degrees of accuracy, and it was difficult to put the measurements together in a coherent and unified fashion. Kepler, through mathematical descriptions, and Newton, with the theory of gravity, were ultimately able to bring the information together in an understandable and relatively simple way. I think the same thing will be done with human locomotion.

As pointed out earlier, science has been applied to prosthetics and orthotics, principally through engineering. From a mechanics viewpoint, all people studying prosthetics and orthotics work under the paradigm of Newtonian mechanics. Other paradigms relate to the theory of structures, theory of machines, electrical circuit theory, and the like. Scientific paradigms may cover large or small areas. Smaller groups, studying specific aspects in the P&O field, may work under what could be called sub-paradigms (e.g., theory of elasticity). It may be that many paradigms in prosthetics and orthotics will develop.

We might speculate about various paradigms that might develop specific for prosthetics and orthotics or for closely related areas. A few may be: a theory of walking, running, and aided ambulation; a theory of human tissue control and loading; a theory of prosthetics and orthotics alignment and load bearing; a theory of appropriate prescription and fit (comfort, function, appearance); and a theory of subconscious control of multifunctional limbs. Childress (1985, 1989) has suggested a general paradigm for prosthetics and orthotics, which his own laboratory more or less uses to guide its studies and development work. The formulation of this paradigm was stimulated by the prosthetic arm design work of David C. Simpson (1974) and by an examination of general methods that seem from experience to work best in prosthetic and/or orthotic fittings. Other paradigms may already exist for the field; for example, I wouldn’t be surprised if some of the concepts of Nickolai Bernstein (1967) might be of this nature. However, most paradigms will likely come about as a result of continued development of the fields.


Science appears at this time to be immature in the fields of prosthetics and orthotics. It has been applied to the fields mainly through engineering approaches. If prosthetics and orthotics are like other fields that were at one time primarily empirical in nature, it is likely that a scientific component will evolve in these fields to augment their empirical aspects. It is predicted that this science, when interdigitated with experience, will have a profound influence on the practice of prosthetics and orthotics during the early years of 21st century.


This editorial was originally presented at the NCMRR Conference on Prosthetic/Orthotic Research for the 21st Century in Bethesda, MD, U.S.A. on July 23–25, 1992. This version of “Applying Science to Prosthetics and Orthotics” has been updated and prepared by the author, D.S. Childress, PhD, as a discussion point about science in prosthetics and orthotics, with permission from the National Institutes of Health, Bethesda, MD, U.S.A.


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                          © 2014 by the American Academy of Orthotists and Prosthetists.