ACADEMY SOCIETY SPOTLIGHT: The Biology of Physical Restoration and Rehabilitation Science

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By Michael Wilson, CPO, LP, FAAOP


athletes stretching

Assessing outcomes for extracorporeal orthotic and prosthetic clinical and technological intervention may seem fairly straightforward. However, the resulting subjective interpretation might not fully capture or accurately reflect the underlying biological issues involved in the physical restoration and rehabilitation of individuals with desensitized or missing limbs. Further, such subjective inquisition does not represent "hard" science, and the results of this method of inquiry are likely to be less than convincing to third-party payers. Thus, there is a need to develop a reproducible, consistent-and most importantly-a predictable method to scientifically test or prove that a specific intervention modality is preferable to another. To do this, we need to find answers to the following questions: What are the underlying biological issues involved in physical restoration and rehabilitation? What makes a mechanical device biological, and how can clinical efficacy of a biomechanical device be physically measured? The answers to these questions lie in understanding how applied biomechanics and neural mechanisms interact to facilitate the correlation of sensory perception skills with normal body imagery skills and to acquire sensorimotor skills to control and manipulate the orthotic, prosthetic, or robotic device.


Physical restoration and rehabilitation of individuals with desensitized or missing limbs is a complicated issue that involves, among other disciplines, mechanical engineering, neuromechanics, biomechanics, neurology, neuropsychology, psychophysiology, clinical and developmental psychology, as well as innumerable medical and therapeutic intervention modalities. Linda Resnik, PhD, PT, director of public health research at Brown University, recently expressed a profound concern regarding the validity and reliability of current clinical outcome assessment modalities. I share her concern because subjective interpretation of physical rehabilitation clinical outcomes is inherently problematic. Furthermore, other than the mechanical measurements, the data being presented for subjective analysis is itself subjective.

All conscious human endeavor is ultimately interpretative and analytical, and thus a personal and subjective experience, but information leading to subjective observation and interpretation must be held fully accountable to the scientific method to the greatest extent possible. The O&P profession is not currently providing this type of objective information.

If we choose to take a biocentric approach to physical rehabilitation, we need to define the essential biological issues involved.

Simply stated, an individual who is successfully physically rehabilitated should conceive of him or herself as whole and normal, perceive or experience the physical sensations of normality, and acquire sensorimotor skills that allow him or her to purposefully, meaningfully, and voluntarily interact with the environment. Body imagery of wholeness has a direct influence on sensory perception. The extent to which an extracorporeal orthotic, prosthetic, or robotic device meets these criteria is the extent to which the mechanical device is indeed biological. In other words, the primary biological purpose of a biomechanical device is to facilitate a sense of wholeness and normality, while the primary mechanical purpose of the same bioengineered device is to effectively support or replace a desensitized or missing limb. Please keep in mind that this is not a strictly, or even primarily, psychological issue. Rather, these issues are manifest in neuromechanical and biomechanical functions. If we were cosmetic surgeons, intervention modalities would inevitably entail psychological issues because the patient not only wants to feel whole and average, he or she wants to feel interesting.

amputees hiking in rugged terrain/mountains

Without conscious perception or acquired conceptualization skills, the subject cannot optimize voluntary interaction with his or her environment when using the orthosis or prosthesis.

Clinical O&P is usually not burdened with this potentially adverse psychology because most O&P patients would like just to feel whole and normal again. (There are exceptions to this rule as pointed out by Mark Geil, PhD, in his scientific presentation titled "Idiopathic Toe Walkers.")

The question then arises: How do we physically measure how well the O&P device facilitates the essential role of biomechanics in physical restoration and rehabilitation? To answer this question, we need to understand the associative and acquisitive interaction between body imagery skills and sensory perception skills. A six-minute YouTube video illustrates how perceptual awareness of our environment is acquired. (Author's note: To view the video, visit

To summarize the video, the subject learns to perceive the physical nature of the objects held in her hand by physical control and manipulation of those objects with her fingers. As she manipulates the objects, she experiences sensations that imply certain features and characteristics of the objects. These sensations are referred to as "implicit sensory experiences," as described by O'Regan et al. in their 2005 paper, "Skill, Corporality and Alerting Capacity in an Account of Sensory Consciousness." These implicit sensations remain at the perceptual level of consciousness until the subject learns to predict or anticipate the interactive relationship between the object's image and what the object feels like. When we associate an image with a sensation, we can think about this as reverse correlation. This interaction has been most recently defined as "Bayesian exploratory skills" by researchers at the University of Southern California, who I spoke with recently. The instant the subject can predict or anticipate how the object's image will be affected by tactile input and how sensory input will be affected by manipulation of the object is the exact moment that the subject acquires a conceptualized or "explicit" sensory awareness of the object, what neural scientists commonly refer to as "conscious perception." In other words, the sensation is experienced as a fully formulated, developed, conceptual, and accurate kinesthetic event. However, in physical restoration and rehabilitation, it is preferable to correlate sensory input with a preconceived notion of wholeness and normality.

At this point you might ask yourself, "What does this have to do with technical and clinical O&P?" It is the correlation of sensory input from the O&P device with imagery that lets the user conceive of him or herself as a whole and normal person. Without conscious perception or acquired conceptualization skills, the subject cannot optimize voluntary interaction with his or her environment when using the orthosis or prosthesis.

skiing amputee

"To really push the [distributed sensing and intelligence] area of medicine, we need to merge body with machine to create an intimacy between the human body and the prosthetic device." -Hugh Herr, PhD

In essence, what the subject learns is neural correlation of sensory emanation biomechanically engineered into the supportive or replacement rehabilitation device with normal body imagery skills or sensations. The primary determinant of neurocorrelation is anticipation of neuromechanical and biomechanical activity. Marcus Raichle, MD, a professor of radiology, neurology, neurobiology, and biomedical engineering at Washington University School of Medicine, St. Louis, has determined that a large fraction of the overall brain activity-60 to 80 percent of all energy used by the brain-is dedicated to predictions about one's body and its relationship to the environment in anticipation of paltry sensory input reaching it from the outside world.

Terry Sejnowski, PhD, an investigator with the Howard Hughes Medical Institute, Chevy Chase, Maryland, uses the phrase "parsimonious energy consumption" rather than "paltry sensory input" to describe basically the same thing: the timing of electrical spikes to encode information and rapidly and efficiently solve neurocorrelation problems. This concept of anticipatory input or timing is corroborated with the "raise to threshold" theory recently postulated by researchers at the Stanford University Department of Neuroscience. In other words, if we can physically measure how well the subject can correlate perceptional skills of sensory information emanating from the O&P device with able-bodied body imagery skills or sensations, we can physically measure rehabilitation efficacy in terms of neurocorrelation coefficients. These "hard numbers," or coefficients, can then be compared with associated monetary expenditure to determine rehabilitation productivity efficiency accurately.


In a 1994 scientific presentation, Deanna Fish, MS, CPO, FAAOP, stated that the dispensation of an O&P device is only 10 percent of what we need to do for O&P clients, and that the remaining 90 percent remains to be done. She made this statement with the assumption that the mechanical properties and characteristics of the device are optimized and that, mechanically speaking, the O&P device provides adequate support for, or replacement of the user's limb. In a subsequent presentation, she also noted that the ensuing 90 percent of clinical care is equally important and significant to the optimization of mechanical design and function. As a profession, we are trained in the mechanical science of O&P. We are proficient in mechanical design and engineering, kinetics and kinematics, and how to couple engineered mechanisms with the mechanical characteristics of the human body. We understand how to control force and motion. But we can also be compared to an electromechanical engineer trying to develop a microprocessor-controlled knee (MPK) with little or no regard for sensory input or how sensory input is processed and used for motor control. The human body acts very much like an MPK knee. Michael Merzenich, PhD, a professor with the University of California, San Francisco, School of Medicine, stated that "we can make smarter prostheses when we are smarter about integrating neuroscience with engineering and medical science," during the National Academies Keck Futures Initiative in his presentation, "Exploring Assistive Devices for the Body and Mind." "Researchers cannot overestimate the capacity of the human brain to restore function, to be trained, to make up what's been lost in extraordinary ways, and with the help of orthotic and prosthetic devices, sensory information can continue to flow into the brain from the peripheral system. Research shows that the brain will learn to use that information for motor control," he further stated.

smiling man running

"[T]he primary biological purpose of a biomechanical device is to facilitate a sense of wholeness and normality...."

In a 2004 lecture, Hugh Herr, PhD, head of biomechatronics at the Massachusetts Institute of Technology Media Lab, identified "distributed sensing and intelligence" as a key area for the future of prosthetics research. "Advances in muscle-like actuators, neuroprostheses, and biometric control strategies are necessary to increase the merging of body and machine to create an intimacy between the human body and prosthesis. It's our thesis that such intimacy will create a paradigm shift in this area of rehabilitation. To really push this area of medicine, we need to merge body with machine to create an intimacy between the human body and the prosthetic device." I have termed the newly proposed rehabilitation science of training, measuring, and recording the subject's ability to anticipate sensorimotor function "neurocorrelagraphy." The development and clinical implementation of this science is not going to be a solo act, but rather a concentrated effort where work and reward are shared by many dedicated and gifted individuals and institutions. I encourage all people involved in physical restoration and rehabilitation to become more interested and aware of, and to participate as much as possible in, this area of rehabilitation science. This is within the professional scope of clinical O&P, and this concept should be more closely associated with and integrated into the O&P profession. There is much to be gained by differentiating between the inherent physiological and biomechanical efficacy of the O&P device (applied technology) and the user's ability and willingness to benefit from this technology (training).

Clinical O&P is an emerging rehabilitation technological specialty, and as such, our profession has the opportunity and ethical responsibility to successfully and effectively incorporate these neuropsychological technologies into our daily clinical practices, especially when these technologies are generated from within our own profession.

Michael T. Wilson, CPO, LP, FAAOP, received a bachelor of science degree in P&O from New York University in 1970, his certification in prosthetics in 1971, and in orthotics in 1972. He has 40 years of experience as a clinical prosthetist and has been an owner/operator of an independent prosthetic clinic in the Houston area since 1984. Wilson holds 24 patents in biomedical, mechanical, and extracorporeal prosthetics and industrial art.

Academy Society Spotlight is a presentation of clinical content by the Societies of the American Academy of Orthotists and Prosthetists in partnership with The O&P EDGE.

Suggested Reading

  1. Haugland, M., and T. Sinkjaer. 1999. Interfacing the body's own seeing receptors into neural prosthetic devices. Technology and Health Care 7 (6):393-99.
  2. O'Regan, J. K., E. Myin, and A. Noë. 2005. Skill, corporality and alerting capacity in an account of sensory consciousness. Progress in Brain Research 150:55-68.
  3. Wilson, M. Sensory substitution/multisensory correlation in physical rehabilitation science.