Powered up: Bionic foot 'natural' for Iraq War amputee
MEMPHIS, Tenn. — Sometimes Greg Mirdo tells people he's one-quarter Terminator. Probably because of the little green light and battery pack attached to his bionic foot.
For five years, the Collierville native who lives in Hot Springs, Ark. has tested several new technologies in prosthetics and is the second amputee in Tennessee — and among only 300 worldwide — to be fitted with the first fully microprocessor-controlled or "bionic" foot.
It's called the BIOM. And it uses robotics to replicate the lost function of calf muscles and the Achilles tendon. It's the only prosthesis in the world that doesn't require the amputee's energy. Instead, it propels the person forward.
"They powered it on, and it felt like my foot was back," said Mirdo, 41, who lost his left leg below the knee to a roadside bomb in Iraq.
"It almost felt natural. It was the most natural I'd felt since I got injured."
The wars in Iraq and Afghanistan have led to a greater population of young amputees who were otherwise healthy and active at a time when research in robotics, biomechanics and other computer technologies were rapidly advancing. The federal government spent millions of dollars on new developments in these areas to help spur the creation of better prostheses for veterans. There have been advances in prosthetic knees, arms and hands as well as feet.
On Jan. 10, 2007, the same day former President George W. Bush announced he was sending 21,500 additional U.S. troops to Iraq, Mirdo was working as a convoy commander with private defense contractor KBR. He'd been there roughly two years delivering everything from fuel to ammunition to troops.
A mile before he got to what was one of the most dangerous roads in Iraq, an alternate supply route called Sword, superheated copper from a roadside bomb blew a hole the size of a soda can in the passenger side door of his armored vehicle.
He never heard the bomb but felt his legs lift in the air. He reached down and felt his right leg. It was sticky. When he tried to move his left, the sensation was like bone scraping the bottom of the cab. He used the mic cord of his radio to tie his own tourniquet but didn't look at the wound.
An ambulance took him to a military hospital where doctors stabilized him before he was flown to the Green Zone. A surgeon there suggested amputation.
"My grandfather was an iron worker during the depression, and he shattered his shin bone," Mirdo said. "They put a rod in his leg, and he was miserable his whole life. That kind of gauged my thinking in the one or two minutes I had to decide yes or no. So I told them to go ahead and take it, and I don't regret it."
That decision — and plenty of physical therapy — led Mirdo to half a dozen different types of prostheses. He started with the most basic, a pipe with a rigid foot that's akin to walking on a board with a little bow in it. Then came one with a spring in the foot and then others with simple pivots at the ankle and finally more complicated ones. Each was more sophisticated than they last, but Mirdo still had to lift the dead weight, which drained his energy.
Then he tried on a BIOM, a $55,000 to $60,000 prosthetic foot that's the most sophisticated ever made. The difference was so pronounced he was willing to lose 30 pounds to meet the weight requirement to qualify for it. It looks like something out of a sci-fi movie.
Mirdo's residual limb fits inside a sophisticated socket made of plastic and carbon fiber material, which attaches to his body through suction. Aluminum and titanium connectors join the upper part of the prosthesis to the BIOM ankle/foot system, which is a combination of steel magnesium and other alloys.
Inside the small, four-and-a-half pound BIOM are four microprocessors and an inertia measurement system that knows its position in space. As Mirdo walks, it senses his movement — backward, forwards, up, down — how much pressure he puts on the device and how quickly he's moving.
To start, it's programmed with basic thresholds that mimic the movement of a normal human leg. Mirdo's prosthetic heel hits the hardwood floor and starts to roll forward. As it gets closer to the toe, a motor that can spin at up to 6,000 RPM. kicks in and propels him forward. When he lifts the prosthesis, the motor powers down, and the process begins again.
The key is to find the sweet spot, which takes some fine tuning. If it's too slow, Mirdo can feel the weight of the prosthesis.
"If it's too fast it feels like it wants to take off and leave me," Mirdo said. "But when it's right, what happens is you forget it's there. The only time I notice that power is when the battery dies and I don't have it."
Dr. Hugh Herr, director and principal investigator of the biomechatronics group of MIT's Media Laboratory, invented the BIOM. He is also founder and chief technology officer of the company called iWalk, which manufactures the prosthesis.
Unlike other bionic technology, which is sales driven, iWalk has limited the number of clinics that are certified to offer the BIOM because the company wants to have control over clinical outcomes. The prosthesis isn't for everyone.
CFI Prosthetics and Orthotics is the only company in Memphis to offer the BIOM. Ted Snell, a certified prosthetist and owner of CFI, has been working with Mirdo to fit the prosthesis since late August.
Snell's family has been manufacturing prosthetics and orthotics in the area for more than 100 years. The technology has come a long way since he started in the business more than three decades ago.
"When we used to adjust the alignment on a leg — I mean I started when they were wooden legs — it was a matter of going to the band saw and cutting it in two, changing angles and gluing things back together," he said.
Now, Snell uses Allen wrenches to pivot the artificial joints but also connects the BIOM to a computer and interprets streams of data that tell him how well it's working. Snell will meet with Mirdo several more times before it's just right.
For Mirdo, whose insurance covered the cost of the prosthesis, the technology has improved his life. His gait looks so natural that if he's wearing long pants people don't know he lost his leg. He's faster, more mobile and doesn't limp, he said. His back hurts less because he isn't overcompensating. And he doesn't get as tired. He has started hiking again.
"I've always been their guinea pig, hoping that anything they learn from this can help somebody else get this foot because it's a great foot," he said.
"It's Terminator technology, I'm tellin' ya."