Molding Miracles

Dave Sisson has been designing prosthetics for over four decades, providing amputees and other clients with a very precious gift: freedom.

From the pages of In Business magazine.
Article By Jan Wilson | Photographs by Sarah Maughan

David Sisson of Sisson Mobility

Dave Sisson makes body parts.

As macabre as this sounds, his three-person company, Sisson Mobility Restoration Center in Madison, fabricates prosthetic parts and braces for patients missing limbs due to natural causes, disease, or accidents.

Sisson, a Chicago native, is not a doctor. He was introduced to prosthetics in high school after landing a part-time job as a technician. He went on to study prosthetics and orthotics (supportive braces) at the City College of Chicago and worked for many years at the world-renowned Rehabilitation Institute of Chicago (RIC) — now the Midwest Regional Spinal Cord Injury Center — as a senior staff prosthetist, where he worked on some of the most difficult cases, including a trans-lumbar (pelvis) amputee.

While there, his youngest patient was still in the womb when doctors discovered she was missing an arm.

He also fitted a 10-month-old child with a myoelectric (sensor-based) movable arm. She adjusted to the device in just 15 minutes by reaching for a toy held in front of her. “You can work with an adult for weeks and never get to that point,” Sisson marvels. “All that intelligence can get in the way.”

But since opening his Madison business in 2000, his work has focused mostly on lower-extremity prosthetics, either above or below the knee. His patients tend to be over 45 and missing one leg below the knee due to diabetes or vascular disease.

Upper-extremity amputees (arms, hands) are less common, Sisson says, although a lot of people are missing fingers. “Typically they’re glued back on.”

Sisson and a technician make everything in house. The art is in casting the perfect fit, he says, especially when it comes to weight-bearing areas.

Temporary legs can cost between $4,000 and $7,000, while permanent versions run between $5,000 and $50,000 on average. Insurance coverage, Sisson reports, “is a pendulum that swings back and forth.”

Extremity Makeover

Sisson Mobility In the company’s laboratory, dozens of feet — or temporary walking aids — in various sizes, shapes, and levels of flexibility are displayed on shelves. At a worktable in the middle of the room, an outstretched arm reaches outward as if begging for a handshake while several detached leg molds are in various stages of production.

“This business is about mold-making and inverse 3-D images,” Sisson says. “I have a pretty good mind for imagining things turned inside out because I’ve done this for 44 years.”

Over a series of fittings, molds are taken of a person’s residual limb to create a perfectly fitted plastic socket. For a prosthetic leg, a gel liner slips over the patient’s skin to create suction. The patient pulls a sock over the liner and inserts their residual limb into the socket. A coupler and metal pin fit through the bottom of the socket, locking the prosthetic leg in place. Aluminum pylons are used so length and fittings can easily be adjusted as a patient grows or shrinks.

Sisson can make a leg in about a week, but fine-tuning will take multiple visits.

A “foot,” measured in centimeters, is attached at the bottom for stability and its placement relative to the patient’s center of gravity is crucial. Twenty-seven centimeters equals a size-10 shoe.

There are artificial legs for everything — riding a bike, swimming, skydiving, and blades for running — but walking, Sisson explains, should be a subconscious activity. “If you change the equipment, you have to think about every step, which is too much effort, in my opinion. Nobody needs that anxiety.”

Function and fit is his first priority. “My personal bias is toward things that don’t require a lot of maintenance, don’t fail catastrophically, and don’t make noise.”

Protective covers made from moldable, flesh-colored foam can be added as a last step in the process to give a metal prosthetic more of a human form, and decorative skins (stars and stripes, John Deere, Harley-Davidson, for example), can also be added on request.

From peg leg to C-Leg

​Sisson says his job is more sculpture than science. Technology has changed immensely since legs were made out of wood and secured to the body with leather straps or waist belts. As recent as the mid-1970s, the only way to adjust a wooden prosthetic was to cut it in half with a band saw, make the adjustment, and glue it back together.

Sisson Mobility

Sisson Mobility

Sisson MobilityMicroprocessors changed the game, providing weight-bearing stability and making real-time adjustments that give patients more natural movement and freedom.

In the late 1990s, Sisson was one of the first in the country to fit a patient with a C-Leg, a device for above-knee amputees. C-Leg’s computer chip actually does the thinking for a patient, he explains, anticipating their next move. “It knows that if X, Y, or Z aren’t happening, it’s not safe for the knee to unlock, which gives a patient stumble recovery and buys them just a few seconds to adjust.” A bent mechanical knee, by contrast, can cause a patient to fall.

All are not created equal

Depending on the patient, an amputation can be more of an inconvenience than a handicap, Sisson says, and every patient is unique. Despite TED Talks to the contrary, there is no one-size-fits-all device. A patient’s age, health, lifestyle, or weight must be taken into account. Some people sweat more than others, for example, which can affect how their skin may react to a liner, some are more active, some can wear a prosthetic all day, while others just a few hours a day.

Rarely does a prosthetic limb last a lifetime.

“The vast majority of patients can wear prostheses all day reasonably comfortably,” he states. “It doesn’t make your life any easier, but you get a lot of your life back.”

Just then, a patient arrives for a scheduled fitting on a myoelectric arm. Wishing to remain anonymous, the gentleman explains that he lost his arm below the elbow in an accident and has been using an electric prosthetic since 1976. His current model is about six years old and powered by a lithium ion battery. It will last three to four days on a single charge, he reports, better than his smartphone.

Illustrating its use, he shuts the battery off at the touch of a button and removes the prosthetic just below the elbow.

Inside the socket, sensors press against his skin to detect electrical impulses fired from his muscle movement. He reconnects the arm and demonstrates as the thumb and forefinger open and close on demand.

Sisson nods approvingly. “There’s a variety of different hands available. Individually motorized ‘Luke Skywalker’ fingers may cost about $50,000 or more. This one costs about $12,000 but has gauges built into the fingertips that will automatically grip an object if it senses that it’s slipping.”

The patient says the technology has given him the freedom and dexterity to do something as simple as tie his shoes. “It holds a beer really well, too.”


Thank you to In Business Magazine for this informative article.
From the pages of In Business magazine.
Article By Jan Wilson | Photographs by Sarah Maughan

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