Bioengineering- Blueprint for Progress
Augustus Thorndike M.D. *
The limbs of man move in space and time,
in response to systems of internal and external forces, and in accordance with
the laws of mechanics. To restore to any satisfactory extent the functions lost
through amputation of an extremity therefore requires intimate knowledge not
only of the structure, form, and behavior of the normal limb but also of the
techniques available for producing complex motions in substitute devices
activated by residual sources of body power. Since adequate replacement of a
natural limb with an artificial one requires successful integration of the human
mechanism with a toollike device, the biomechanical features of the stump and
the physical characteristics of the prosthesis must be wedded as nearly as
possible into a single, functional entity.
Two-sided as this problem would now
obviously appear, it is only in comparatively recent years that the medical
sciences of surgery, anatomy, and physiology and the physical one of engineering
have been brought together in a unified attack upon the whole problem of amputee
rehabilitation. Until recently, surgeons, with few exceptions, had little or no
understanding of engineering problems. And heretofore the design and
construction of artificial limbs has been conducted mostly by artisans who,
however ingenious they may have proved to be, were mostly without formal
education in engineering or anatomy. Besides this, except in isolated instances
the two worked separately and alone. All of which no doubt accounts for the fact
that, as late as World War II, the available artificial limbs fell far short of
the standards of accomplishment attained in other fields of research and
invention.
In the research program coordinated by
the Advisory Committee on Artificial Limbs, National Research Council, there
have been brought together in harmonious working relationship the individual
skills of surgeon and engineer in a sort of mutual bioengineering to produce
truly functional artificial limbs. As a result, there has been in the field of
prosthetics perhaps more progress during the past decade than in all the
preceding 2000 years of limb-making.
Because the lower limb is more essential
to human activity than is the arm, and also doubtless because the basic
functions of the leg are easier to replace than are those of the arm, progress
in artificial arms and hands has from the earliest times always lagged far
behind developments in artificial legs. This circumstance was reflected in the
fact that, when the Artificial Limb Program was established in 1945, much more
had already been accomplished in replacements for the lower extremity than in
those for the upper. And consequently developments in the ACAL program to date
have been most noticeable in upper-extremity prosthetics, despite extensive
engineering studies of normal and amputee locomotion and refinements in the
techniques of lower-extremity fit and alignment.
In any case, the development of
prosthetics had necessarily to follow the pattern of developments in surgery,
and conversely the surgeon's philosophy with regard to "sites of election" and
other matters was necessarily dictated by the character and availability of such
prostheses as there were. Since the science of amputation surgery and the art of
limbmaking proceed as one, the standards and practices in one field dictate
standards and practices in the other, and vice versa. That each of these has now
been brought to understand more fully the problems of the other may be looked
upon as a major achievement in the art of prosthetics.
In the following pages of this issue of
Artificial Limbs is to be found substantial evidence that the engineering
profession, working with the amputation surgeon, has provided new thoughts, new
ideas, and new approaches to the problem of providing adequate functional
replacements for the limbless. In the whole Artificial Limb Program there exists
no better example of cooperation toward progress than is demonstrated here. In
the first of two articles, a surgeon and an engineer collaborate in describing
the latest devices and techniques arising from systematic research and the
influence which these developments ought rightly to exert upon the philosophy of
modern amputation surgery. In the second, an engineer outlines the methodology
required in investigation of the normal limbs and in the design of useful
replacements. Only through such teamwork in biomechanics can truly great
advances in the field of prosthetics be expected. The development of the thirty
Veterans Administration and other civilian orthopedic and prosthetic appliance
clinic teams has resulted in the better distribution of new knowledge toward
improved fitting and alignment of artificial legs and in the design and
construction of improved artificial arms.
The program of research coordinated by
the Advisory Committee on Artificial Limbs involves the participation of
government, university, and industrial laboratories. The Veterans
Administration, the Army, and the Navy provide the necessary funds for the
operation of their own establishments, while the VA provides the contractual
authority with the funds necessary for work in the universities and in
industrial laboratories. Out of this cooperative effort there have come within
recent years improved functional prostheses for almost every level of
amputation, particularly for those special amputee cases heretofore considered
unsuited for an artificial limb. With the mutual cooperation of surgeon and
engineer, there has resulted a cross-fertilization of ideas and a new set of
modalities in the rehabilitation of amputees.
Nevertheless, the presently
available devices, though anthropomorphoid in form, are far from
anthropomorphoid in function. Unfortunately, no artificial limb, however
elaborate, can ever serve as an ideal substitute for a natural member unless it
incorporates some of the features of sensory and muscular control characteristic
of the limb it replaces. Therein lies the challenge of the future- to devise
mechanisms which not only simulate the motions and the functions of normal limbs
but which also provide appropriate feedback of information such as occurs in
natural arms and legs. In our present state of knowledge, the ultimate goal of
the limb designer is still a long way off. Further progress depends largely upon
the continued cooperation of surgeon and engineer, of prosthetist and therapist,
and of the amputee himself.
|
