Developing Transfemoral Cycling Prostheses for a Cross-Country Journey
In this edition of Shop Talk, The O&P EDGE shares a prosthetist's creative solution for adapting lower-limb prostheses and a bicycle for his patient's cross-country journey.
I met Rob Jones in 2010 while I was the chief prosthetist at Walter Reed National Military Medical Center (WRNMMC), Bethesda, Maryland. He has a left knee disarticulation and a right transfemoral amputation, the result of injuries sustained during his deployment to Afghanistan with the U.S. Marine Corps Reserve. After Jones transitioned from using prosthetic shorties to using definitive prostheses with microprocessor-controlled knees (MPKs) independent of assistive devices, he decided he was ready for a new physical challenge: cycling. His challenge was also my challenge-it would test my skill in providing appropriate prosthetic devices.
In 2011, around the same time that Jones decided to pursue cycling, I was working with two other patients with bilateral transfemoral amputations who were getting back into cycling. One of them, a Marine like Jones, also had bilateral upper-limb amputations, and we decided that a recumbent bike would be most suitable for him-for safety's sake when mounting and dismounting the bike. For Jones and the other patient, a Navy Seal and former triathlete, we opted for upright bicycles.
Each of their prosthetic designs incorporated subischial sockets for comfort around the seat; Leftside Industries' Bartlett Tendon Universal Knees (BTKs) for strong and durable extension assist; and custom, non-split Össur LP Vari-Flex® carbon fiber feet with recessed pedal cleat attachments and soling material glued directly to the bottom for reduced weight, improved power to the pedal stroke, and ease of clipping in and out. To check the functionality of the prosthetic designs I had chosen, I mounted the bikes to stationary trainers and assessed each patient's ability to pedal. For all three, pedaling backward was easier than pedaling forward, which perplexed me.
This was such a source of frustration for me that in the evenings after work, I sketched out possible solutions and even made a mechanical model out of LEGOs® and rubber bands. It took me a couple of months, but I was sure I had found a solution, so I called Brian Bartlett, inventor of the BTK, and told him my idea. About two weeks later, he was in my office helping with my three patients, and we solved the problem of pedaling backward. What I realized was that a person with a transfemoral amputation does not have the quadriceps function to extend the knee beyond the 12 o'clock position in the pedal stroke. The solution was to limit flexion past 90 degrees and "bump" the knee back over the top. Brian and I did this on each BTK by inserting a special bolt with a urethane bumper insert. On Jones' left knee disarticulation socket, I used a piece of an extra Bartlett tendon band as a 90-degree bumper. This worked for all three men, and we thought we had discovered something that could change transfemoral cycling biomechanics.
Shortly after discovering this breakthrough, I started working more closely with Jones, who had received a new bike from Ride 2 Recovery (R2R). Ray Clark, R2R program manager, was instrumental in adjusting the bike to Jones' needs. He changed the road bike handlebars to flat bars with ergonomic grips to allow for an upright position. The gear ratio on the back cassette was lowered, making it easier to pedal. Crank arm shorteners were added, and the seat post was replaced with a remote-release telescoping post, which allows up and down motion of the seat height from a push button on the handlebars.
Jones' current prosthetic designs incorporate bilateral subischial trim lines with a transfemoral double-wall socket on the right leg, and a suspension sleeve knee disarticulation socket on the left leg. The right knee is a BTK with a modified flexion stop and the left is a design that uses Ottobock external hinges and a Bartlett tendon band stretched across the socket to below the knee with 90-degree stop. We put Speedplay pedals on the bike because they proved to be the easiest to clip in and out of.
I felt good about conquering the biomechanical conundrum. However, transitioning from riding a bike affixed to a trainer to a freestanding bike was another obstacle. WRNMMC's rehabilitation facility is equipped with a circular Solo-Step ceiling-mounted track system and harness that Jones used to practice mounting and dismounting the bike in a controlled environment. At one point during that session, the pulley got caught in a kink in the track, and Jones actually flipped over backward. Although he wasn't hurt, he was a little shaken up. By the end of our second practice day, however, he was not only able to mount and dismount, but to start and stop by himself. At this point, he picked up his bike overhead and we thought he'd achieved enough to have fulfilled his goal-looking back, I was completely wrong.
Clark and I took Jones out on some ten- to 15-mile training rides on the weekends. Although we had to wait for him, especially after going up a hill, he persevered and maintained his balance. As his comfort level on the bike increased, we were invited to participate in a mini triathlon hosted by the Center for the Intrepid, San Antonio, Texas, in conjunction with the Challenged Athletes Foundation. In September of that year, Jones returned to Washington DC, and competed in The Nation's Triathlon.
Jones finished his rehabilitation, left WRNMMC, and spent time pursuing another of his athletic ambitions, Paralympic rowing. Along with his rowing partner Oksana Masters, he won a bronze medal in the 2012 Summer Paralympic Games in London, England, in mixed double sculls. After having attained that goal, he returned to cycling with another goal in mind: to ride across the country-from Maine to California-and raise money for nonprofit organizations that provide aid to veterans and had aided him in his recovery, including the Coalition to Salute America's Heroes, the Semper Fi Fund, and R2R.
His goal was to cover about 30 miles a day and complete the trip in less than six months-and he succeeded. (Editor's note: Jones began the cross-country ride in Bar Harbor, Maine, on October 14, 2013, with his brother, Steven Miller. They arrived in Camp Pendleton, California, on April 12, having cycled nearly 5,300 miles. You can learn more about Jones' journey at www.robjonesjourney.com)
As Jones embarked on his journey, I worried about how well his prosthetic legs would hold up, and it turned out I was right to worry because his trip was not without some hiccups. In Pennsylvania, WRNMMC sent Jones a new Bartlett band via express service; in Missouri, he needed screws for his Ottobock hinges; he broke a BTK in Kansas; and then he broke his backup knee in Utah. Bartlett drove from Seattle to surprise Jones and to ride with him in Utah, supplying him with a repaired knee. I made a last-minute trip to San Francisco, California, to replace the external Ottobock hinges damaged by rust and bearing loss just 550 miles before the end of his trip.
When I met Jones in San Francisco, we decided to try removing the left 90-degree flexion stop. The stop on the right side had already broken off and he felt he didn't need it. He also wasn't using the shock on the BTK. I replaced the hinges and we tested the configuration without the stops. He said his pedal stroke felt smoother. I am once again perplexed about the need for the 90-degree stop. Perhaps Jones has developed an efficient pedaling technique that no longer requires the mechanical assist getting over the top of the pedal stroke.
I've talked to Jones about his possible interest in training for paratriathlon with an eye toward the 2016 Summer Paralympic Games in Rio de Janeiro, Brazil. He seems interested. While I still would like to deepen my understanding of the biomechanical intricacies of transfemoral cycling, through my experience with this project and subsequent exploration, I have learned a few things:
- The knee center should fall closely to half the distance between hip center and pedal center.
- Seat height is critical. For a person with bilateral transfemoral amputations, lower seat height makes mounting and dismounting the bike easier; however, it can cause a tendency to pedal backward. Thus, a hydraulic seat post is a good option.
- An upright bike geometry is preferable to an aero position.
- Clip-in pedals, and perhaps prosthetic feet without shoes, are ideal.
- A flexion and extension assist, using a material such as the BTK, may be beneficial to pedal stroke smoothness and efficiency.
- Never underestimate a Marine! This doesn't apply to all transfemoral cycling of course, but it definitely applies to Jones.
Zach Harvey, CPO, is the managing CPO of the Denver, Colorado, branch of Bulow Orthotic Prosthetic Solutions location. He was previously the chief prosthetist for Walter Reed National Military Medical Center, Bethesda, Maryland, and has served as an adjunct professor in the physical therapy program at George Washington University, Washington DC.