Building a Track-Serviceable Running Prosthesis
March 2009 Issue
|Steven Wilson and Jim Bob Bizzell compete in the 200-meter sprint in Beijing.|
If a NASCAR team built a race car and prepared it for the track, they wouldn't weld the hood shut before they sent it out to the race....The same principle holds true for sprinting prostheses. Why laminate the plate of a sprinting prosthesis?
During the Atlanta Paralympic Games in 1996, I was the prosthetic technician for one of the elite athletes. From that point on, I was hooked. The Paralympic Games have been a big part of my life ever since. However, having attended every Paralympics since Atlanta did not prepare me to be chosen as Team USA's prosthetist for the 2008 Paralympic Games in Beijing. For the first time, I would have the opportunity to stay in the Paralympic Village with the athletes and become a true part of the venue, from the opening ceremonies to closing.
Working with Paralympians in Beijing
As Team USA's prosthetist, I was responsible for ensuring that the athletes were up and ready on time and that their prostheses were in top condition for their competitions. This was no easy task. I worked with the athletes at the track long before their events started and long after their races were run. I was on call constantly to make the necessary adjustments to ensure that the hard work of these athletes, who had been training for years, was not in vain. On television, viewers might watch a race such as the 100-meter sprint and see the event take place in as little as 11 seconds. In reality, however, events like this were taking place from 7 a.m. to 11 p.m., and I, along with the other Team USA staff members, were working at the Bird's Nest or at the adjacent practice track for 15 or more hours every day. For emergency cases, Otto Bock HealthCare had set up a 2,000-square-foot temporary lab with componentry, which was available to me to fix problems for the athletes. But because the lab was located in the Paralympic Village-a one-hour round-trip bus ride/walk from the Bird's Nest-it was difficult to deliver a repaired prosthesis to an athlete in time for his or her event. To make the best use of my time, it became apparent that I should carry most of my tools and supplies with me and only go to the lab when absolutely necessary. This allowed me to help more athletes at the venue where they performed and where the majority of problems could occur.
Addressing Technical Challenges
|Jerome Singleton and Jim Bob Bizzell take a victory lap after winning the 4x100 meter relay.|
Another thing that became apparent to me is the need for a more unified way of designing track-and-field prostheses. On a track-and-field sprinting prosthesis, the foot is typically bolted onto the posterior part of the frame, with two bolts sinking into a plate that has been laminated onto the socket/frame. This is the design I have used ever since Curt Collier, CP, explained to me in the early to middle 1990s how to laminate a Symes plate into the back with two female T-nuts buried into the carbon fiber plate. Then you would laminate the Symes plate in and drill through the exterior lamination to bolt the foot onto that.
That system works very well until you need to adjust the angle of the foot by either turning it in or out, or plantarflexing or dorsiflexing it. If that kind of adjustment is needed, you must unbolt the foot and re-bolt it back in, which increases the likelihood that the bolt will eventually strip at the threads on the inside plate of the lamination. While in Beijing, we had three prostheses' plates strip out on the inside-Jerome Singleton's, Brian Frasure's, and Marlon Shirley's-two of which were laminated in and inaccessible. When Jerome Singleton's prosthesis stripped out at the female T-nuts on the inside of the plate, the practitioner in charge of prosthetic repair at the Okinawa, Japan, training and warm-up camp wrapped the prosthesis with fiberglass tape, which was the only feasible solution without re-laminating the entire leg. This added a lot of weight to Singleton's prosthesis. Because our team did not have access to a lab at the time of the training camp, we were forced to make quick, extensive fixes. When the same thing happened to Brian Frasure's prosthesis only two days before competition in Beijing, we decided to strip off the whole exterior lamination, cut out the plate, replace the plate, and re-laminate it all back together, which is the way it should have been done. However, it is very risky to completely remake a runner's prosthesis at any competition, let alone the Paralympic Games.
|This drawing shows the trap-door technique used in Scott Sabolich sprinting prostheses.|
The 'Trap-Door' Prosthesis
In my years of dealing with Paralympic prosthetic designs, I've discovered a way of making them more track serviceable. The ideal way to handle this is exemplified by how we fixed Marlon Shirley's sprinting prosthesis when it needed adjustments. Shirley's prosthesis has what we call a "trap door," a common term among Sabolich Paralympic sprinters. Many U.S. prosthetists are unaware of this technique and instead think it is best to do an initial lamination, add the plate, and follow with a second lamination.
The trap-door technique makes a sprinting prosthesis more modular and easier to work on trackside, when time counts the most for athletes. Think of it this way: If a NASCAR team built a racecar and prepared it for the track, they wouldn't weld the hood shut before they sent it out to the race. If something were to break, the repair team would have to cut through the hood just to access the area that needed to be fixed. The same principle holds true for sprinting prostheses. Why laminate the plate of a sprinting prosthesis?
|Sabolich patient Katrin Green competes in the 200-meter sprint.|
To fabricate a trap-door prosthesis, you simply make a "door" larger than the lamination plate you are already adding at the time of your first lamination. We often first pull a thin Surlyn socket over the mold to go right against the liner and to protect it from the carbon fibers of the frame. Laminate the door only and then set it on the Surlyn socket or onto the cast if no socket is needed. Then, build up with plaster onto the door where the plate is. Make the second lamination over all of it, including the plate, and then when you break out the plaster, youll have a trap door that houses the Symes plate. If the Symes plate strips, you can simply pull that plate out, replace it, put the trap door back in, put the socket back in, and you are done.
If prosthetists across the United States built prostheses more uniformly, I believe the prostheses would be much more accessible during the 2012 summer Paralympic Games in London-or at any track and field competition for that matter. The end result could mean more wins for your elite athlete patients and more gold for Team USA in 2012!
Scott Sabolich, CP, LP, is the owner and clinical director of Scott Sabolich Prosthetics & Research, Oklahoma City, Oklahoma. For more information about Sabolich's facility or for guidance on alignment, setup, or design, call 405.841.6800, e-mail: firstname.lastname@example.org , or visit www.scottsabolich.com
Photographs courtesy of Scott Sabolich.