University of South Carolina

Each year the University of South Carolina's engineering college sponsors a university-wide essay and art contest that promotes the integration of engineering and the humanities. "Designs in Motion" was the 1997–98 contest theme, and the winning essay was submitted by Albin Johnson, Jr., at the time a junior in electrical engineering. In July 1994, Johnson was in an auto accident and suffered permanent injury to his left leg. His winning essay, which follows, talks about the engineering behind the artificial leg he now uses. 

Alexander Pope once wrote, "What mighty contests rise from trivial things." The statement presumably invites one to reflect on how conflicts have arisen from matters that, in retrospect, seem petty compared to the struggles they seek to justify. But if the 20th century is any indication, another interpretation could be that many things once considered trivial have gone on to inspire efforts greater and more laudable by far than the seeds of their inspiration.

Take the transistor. In 1947 two Bell Labs scientists assembled some semiconducting material, gold foil, and a paper clip, and managed to control the flow of electrons in a way that revolutionized computer technology—an industry that pervades every aspect of our society today. Within 20 years Fairchild Semiconductor found the ideal substrate for integrated circuits in commonplace sand, solving a frustrating thermodynamics problem and opening the way for large-scale microprocessor production. These discoveries are said to be important steps in shaping modern technology, but in my opinion it is the mundane topic of the "step" itself that has inspired some amazing feats in technology today. I'm referring to the physical act of taking a step.

Most anyone can relate to the simplicity of walking. It is that redundant ambulatory routine that separates us from lower life forms and is so forgettable that we somehow learn it at an age when our brain isn't even fully developed, then relegate it to the reflexive corners of our behavior. Yet it is the result of millennia of evolution, a design process that has engineered thousands of delicate synergistic mechanisms working together with the crude medium of bone and sinew to create a fluid art form. It is a process we too easily take for granted, both for its usefulness and complexity.

A Sudden Halt
My first lesson in studying this underappreciated art form came in July 1994 when an auto accident permanently devastated the engines of my motion below the knees. The left leg was deconstructed all the way to its supporting structure of bone; the other lost 15 percent of its muscle tissue and most of its nerve connections. Suddenly a highly efficient design was compromised beyond all hope of repair, and the original architect behind it had left no plans for its restoration. Enter prosthetics.

In few other areas of science do matters of life and technology meet so intimately or as deliberately as in prosthetics. The field of ergonomics tends to overuse the term "human engineering" to describe machine designs accommodating human form. Compared to the scope of engineering involved in physically marrying human and machine, this is trivial. Prosthetics, quite simply, is the machine design simulating the human form in all its complexities. It can be argued that it is the true human engineering. I would come to learn this firsthand.

My first year and a half after the accident was spent salvaging what function remained in the shattered mechanisms that had been my birthright. The right leg, in spite of the failure of electrodes to stimulate it back to life, repaired itself to some extent. Vital motor and feedback connections of the nerve cells branched out along a new route near my knee. The tattered, gutted remains of the muscle bodies in my calf were so dynamically interwoven by design that a new, albeit improvised, workhorse emerged to power the foot and knee.

The left leg, however, would never recover. Pounds of muscle were requisitioned from other parts of the body to shore it up, bone grafts to buttress the massive fractures, and sheets of skin to seal in a system too devastated to even produce its own covering. What resulted was a poor imitation of the original and one that worked in form only. A brace was prescribed. Heavy metal struts running along the outside of my leg, from my knee to my ankle, and ending in a large boot, struggled to do the work that a few centimeters of bone that wouldn't grow back used to do. Function was limited to halting steps, improvement was doubtful, and the solution seemed worse than the problem. It was time to think outside the circle.

An irony pointed out to me was that amputees enjoyed far better mobility with artificial limbs than I ever would with my salvaged original one. I couldn't believe this at first. How could anything man-made replace a member of my body that technically was still functional?  The gestalt of the human form that I held, that we all hold as human beings, couldn't approve the price of sacrificing my "greater whole" to gain mobility from a separate part. Yet, there it was. A solution to almost all my problems, only a single psychological hurdle away. One of the most important steps I ever took, figuratively or literally, was signing the paper to have the ruined machinery removed.

Renewed Accessibility
What awaited me was a world of possibilities. Far removed from preconceived notions of peg legs and crude hooks, today's artificial limbs benefit from decades of improvements in structural engineering, alignment, socket design, strength of materials, and componenture. The "Space Age" produced unexpected side benefits for the field of prosthetics. High-impact polymers replaced expensive metal parts that can't form flexible seals; carbon fiber laminates became crosswoven and cast in a variety of shapes for load distribution of any limb residual; and titanium replaced steel and aluminum for its light weight and durability. Add to that the power of computers to simulate the load-bearing and alignment of the leg as it moves, which led to the preflexing socket and the adjustability it lends as the patient moves.

My trip to the 1996 Summer Paralympics in Atlanta, the handicapped corollary to the standard Olympic games, was an epiphany. I saw amputees functioning in a way that shattered every stereotype I held about them. There were sprinters soaring down the track atop keel feet, struts of titanium curved like a recurve bow. The curvature absorbs enormous pressure when weight is thrown onto it and, unlike an old wooden leg, has a resilient flexion design that stores the energy of every step and returns it like a spring as the runner vaults into his or her next stride. Sometimes the energy return can be even greater than that of a normal foot.

Other events showcased the more conventional Dynamic Response Foot. Its ankle has several degrees of rotation to simulate a normal foot, a marked improvement over the traditional uni-actual Sach foot used only by beginning amputees today. A hydraulic knee module can control the weight tolerance of the leg if designed for amputees that have no knee. And for high-impact activities, vertical shock pylons can be added, which again use hydraulics to absorb the shock of impact without wasting the energy from the step.

What impressed me most as the premier accomplishment of leg prosthetics in the computer age, however, had to be Endolite's Intelligent Prosthesis (IP). Amputees without a knee have little control over foot placement, having to "throw" their leg forward to return the foot to ready position for the next step. The IP leg has a motor for returning the lower leg and is attached to a microprocessor-controlled sensor linked to the patient's thigh muscles. When the muscles flex, as they normally do when taking a step, the motor is activated and the foot brought forward automatically. A remote control can be used to program the leg's resistance level, raising and lowering it based on the user's activity level.

As I soon learned, I had less to fear from my new life than I thought. I adapted quickly to my artificial limb and now enjoy near-perfect gait. Every step I take is a study in kinetic and mechanical principles once taken for granted, a synergistic contest powered now by the sophisticated engine lent to me by another architect, the collective mind of all the engineering that went before it. Not so trivial after all.


In Brief

As a sign of its commitment to study-abroad experiences, Worcester Polytechnic Institute (WPI) is giving all incoming freshmen a voucher for a free U.S. passport. Robert Voss, WPI executive director of admissions and financial aid, says the new offer is part of the school's efforts to "attract students who understand that having a global perspective and experiencing cultural diversity is important."

A retired Intel Corporation circuit fabrication operating line is getting a second life as a teaching tool at the University of Illinois at Urbana-Champaign (UIUC). Electrical and computer engineering students use the donated $1.4 million operating line to fabricate circuits on silicon wafers. The laboratory is one of only four undergraduate instructional silicon wafer labs nationwide, according to George Bourianoff, Intel's manager of U.S. academic relations.

return to PRISM online; or October PRISM online