Studies have shown that 52% of community-dwelling amputees will experience at least one fall within the first year of their amputation, and this risk may be amplified for bilateral amputees.

“As I reviewed our laboratory videos of individuals walking with bilateral transtibial amputation, I noticed that they displayed quite exaggerated upper body movements,” Matthew J Major, PhD, research fellow and instructor at the Northwestern University Prosthetics-Orthotics Center (NUPOC), told O&P Business News. “This has been clinically observed, but until out study it was never quantified.”

Especially with the dearth of research about bilateral, transtibial amputees, Major wanted to further investigate how these upper body movements affect gait and balance.

“We started to examine exactly how exaggerated trunk motion might affect their balance and stability. We know that individuals who walk with lower limb prostheses experience reduced sensory mechanisms that negatively impact their upright balance and postural control,” Major said.

Matthew J. Major

Reduced step width

Major and colleagues performed a retrospective analysis of 10 bilateral, transtibial amputees. The participants performed overground walking trials on a 10-meter walkway at three self-selected speeds: slowest comfortable, normal and fastest comfortable. The participants also performed these walking trials with two prosthetic configurations: first while wearing the Seattle Lightfoot II prosthetic foot and again while wearing the Seattle Lightfoot II, Endolite Multiflex ankle and Ottobock Torsion adapter.

“We had each participant walk with two sets of prosthetic components that reflected differences in rigidity,” Major said. “The second set included prosthetic adapters that provided increased motion at the ankle joint.”

After analyzing video footage of the participants walking with the various conditions, Major noted that all of the participants demonstrated exaggerated lateral trunk flexion while walking.

“One of our findings was that these individuals displayed a substantial increase in the range of motion of lateral trunk flexion when compared with able-bodied controls.”

According to Major, the average able-bodied walker exhibits anywhere from 2° to 4° of lateral trunk flexion, but the amputees in this study were averaging 11° of lateral trunk flexion.

“Given this substantial increase, we were interested in identifying how walking speed and also changes to their prosthetic componentry affected lateral flexion,” Major said.

As they analyzed the participants’ gait further, the researchers discovered the participants reduced their step width as they walked at faster speeds, as well as when the prosthetic ankle adapter was introduced.

“An interesting finding was that when the participants reduced their step width, the exaggerated lateral trunk flexion remained invariant,” Major said. “This suggested to us there may be some added benefit to walking with this lateral flexion.”

However, this exaggerated postural sway combined with a reduced step width increases the risk for falls, because the base of support is reduced.

“As these individuals reduce their step width and maintain this large lateral flexion, they are pushing their extrapolated center of mass beyond the base of support,” Major said. “The risk in this case is that as the extrapolated center of mass extends beyond the base of support, these individuals may be more prone to a fall if subjected to an external perturbation, such as a sideways push.”

Active prostheses

Major believes that the exaggerated sway demonstrated by the individuals in this study resulted from their use of passive prosthetic devices.

“This exaggerated movement from side to side seems to provide some benefit in that it unloads the trailing limb and allows them to transfer the weight onto their stance limb and then advances the trailing limb to become the leading limb,” Major said. “We think lateral trunk sway among the individuals in this study may be explained by their use of passive prostheses that contribute no active energy, thus increasing the difficulty of trying to advance the limbs forward.”

Future studies are needed to confirm this, but Major suggested the use of active prosthetic components for this population could reduce postural sway.

“Knowing these individuals have compromised balance and postural control as a result of walking at increased speeds and with certain prosthetic adapters, we recognize what we can do to improve their upright balance,” Major said. “Potentially, this will provide additional insight into prosthetic prescription guidelines.”

These results could also have clinical implications for developing gait training methods to reduce lateral sway.

“In both of these cases, I would like to determine whether effectively reducing this exaggerated trunk motion will allow these individuals to maintain efficient forward ambulation,” Major said. “There is still a lot of work that needs to be done, but the most important objective is to improve functional balance and reduce the high prevalence of falls in this population.” — by Megan Gilbride