A Call to Improve Advanced Science Content: Part II

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Editor's Note: "The capabilities of any technical profession are highly dependent on the quality of the science underlying it." With this thought in mind, Edward S. Neumann, PhD, issued a call to expand and improve the advanced science content of O&P curricula in an article published in the July issue of The O&P EDGE. In this issue he provides an in-depth examination of four of the seven areas in which he feels upgrading and expansion are needed. A discussion of the last three areas, along with Dr. Neumann's recommendations and conclusions, will be published in the September issue.

Biomechanical Tissue Factors

Biomechanical tissue factors of importance include the engineering properties of tissues, their composition, strength, requirements for nourishment, and most important, how they respond to load.

In my opinion, the development of classroom materials on tissue properties and behavioral characteristics is one of the most urgent needs in prosthetics education. The O&P practitioner purposely applies external loads of a magnitude great enough to potentially cause discomfort and necrosis to areas of the body that were not designed to carry such loads. All practitioners should have knowledge of the basic biomechanical concepts associated with, and scientific work that has been conducted on, tissue loading and its consequences.

With the proliferation of socket liners, materials, and suspension technologies available in today's market, the practitioner's ability to ask suppliers the right questions and to develop informed judgments depends upon a basic understanding of tissue biomechanics and physiology. Socket fit challenges created by redundant tissue, edema, shrinkage, scar tissue, skin grafts, and invagination should be analyzed from a biomechanical perspective utilizing tissue property concepts. The relevance of the concepts of shear force and the coefficients of friction associated with different materials should be presented.

Candidate sources of content include: the classic book by S. W. Levy, on Skin Problems of the Amputee; the series of articles by L. Bennett on the effects of shear stress and the more recent work by J. E. Sanders on this topic; the tissue properties and finite-element modeling studies conducted by D. Childress, B Silver-Thorne, S. G. Zacharia, W. M. Vannah, A. F. T. Mak and Y. P. Zheng; and the classic studies on friction blisters undertaken for the military. The biomechanical parameters, experimental methodologies, and findings that appear in these studies, as well as their limitations, should be distilled and presented to the student.

The science of osteo-periosteal bone bridge techniques would also fall within this category. Knowledge of tissue biomechanics will become essential if prosthetic limb osseointegration techniques are introduced in the United States. Radiography, the most recent addition to the National Commission on Orthotic and Prosthetic Education (NCOPE) requirements, might fit in the tissue biomechanics category as well.

Theoretical models of socket pressure distributions for the family of lower extremity prostheses were developed by C. W. Radcliffe, and every student should be familiar with them because they indicate locations within the socket where tissue tolerances are most likely to be exceeded. Although a lack of reliable and inexpensive socket pressure measurement systems for many years limited research into socket biomechanics, a number of studies were undertaken and published. Usually these studies examined tissue properties. Recent advances in the state-of-the-art socket pressure measurement may facilitate new studies that could expand upon the earlier theoretical work and make pressure measurement a useful everyday tool for the clinic. The tissue biomechanics category offers considerable potential for advanced science courses.

Biomechanical Gait Factors

Biomechanical gait factors concern the effect of pathology and component design characteristics on the kinematics and kinetics of gait. Most curricula currently contain information on the analysis of gait derived from research conducted by V. T. Inman, J. Perry, and others during the last five decades. However, a significant number of scientific studies have been conducted more recently using sophisticated human motion analysis systems to examine the effects of different prosthetic and orthotic component designs on gait. These studies have been published in both the O&P journals and medical and rehabilitation journals. Collectively, these articles describe the state-of-the-art in gait measurement and assessment in the context of O&P science and form a universe of relevant concepts, research hypotheses, and conclusions from which a subset could be extracted to serve as the basis for educational materials.

A thorough review of these studies that points out the differences among them with respect to variables controlled for, variables researched, and findings, could lead to improved research hypotheses and perhaps ultimately to better clinical tools for assessing patient needs and characterizing the components being marketed. Gait-related biomechanical factors also involve the challenges created by level of amputation and limb length.

Physiologic Factors

Physiologic factors are related to the constraints created by underlying pathologies, which may be the reason for amputation and may also limit the activity levels of individuals via circulatory, metabolic, or respiratory insufficiencies.

Some pathologies and the treatments for them create fitting challenges by causing major volume fluctuations in the residual limb, changes in blood chemistry, or a lack of sensation. Components which require higher energy expenditures can conflict with the physiologic limitations of patients who have circulatory or respiratory disorders. A number of articles have been published in the rehabilitation literature on the comparative energy costs of different component designs, as well as the comparative energy costs of different levels of amputation.

Students should be aware of the energy cost implications of both amputation level and component selection, because they can influence outcomes among geriatric patients as well as highly active individuals. The published articles are a good source of information on the relevant concepts from exercise physiology, the variables involved and their relationships, and the magnitude of the impact that can be expected from alternative component designs.

Psychophysical Factors

Psychophysical factors involve the neurophysiologic mechanisms by which sensations are produced and evaluated to form judgments of discomfort.

Important subjective phenomena include sensations of pressure, tightness, heaviness, temperature, moisture, and pain. Knowledge of the neurophysiology underlying pain and pressure sensation can help the clinician to better interpret the discomfort symptoms of patients, and should therefore be viewed as essential to clinical practice.

Although psychophysical phenomena have been overlooked in O&P research, the patient is very much aware of their importance. Ergonomic science has established that psychophysical phenomena underlie many of the judgments individuals form with respect to the maximum amount of applied force and level of exertion they can tolerate; frequently these subjective judgments do not agree with tolerance levels predicted purely by biomechanical or physiologic models. O&P science should introduce the student to the basic concepts and measurement methods of psychophysics, and indicate its relevance to clinical practice.

Edward S. Neumann, PhD, PE, CP, professor of Civil and Environmental Engineering at the University of Nevada, Las Vegas (UNLV), is currently involved in efforts to establish a degree program in biomedical engineering at UNLV. He is developing and teaching courses in prosthetic systems, assistive technology, and ergonomics.

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