The effects of ground-irregularity-cancelling prosthesis control on balance over uneven surfaces

Abstract

Over half of individuals with a lower-limb amputation are unable to walk on uneven terrain. Using a prosthesis emulator system, we developed an irregularity-cancelling controller intended to reduce the effect of disturbances resulting from uneven surfaces. This controller functions by changing the neutral angles of two forefoot digits in response to local terrain heights. To isolate the effects of the controller, we also programmed a spring-like controller that maintained fixed neutral angles. Five participants with transtibial amputation walked on a treadmill with an uneven walking surface. Compared with the spring-like controller, the irregularity-cancelling controller reduced ankle torque variability by 41% in the sagittal plane and 64% in the frontal plane. However, user outcomes associated with balance were mostly unaffected; only trunk movement variability was reduced, whereas metabolic rate, mediolateral centre of mass motion, and variabilities in step width, step length and step time were unchanged. We conclude that reducing ankle torque variability of the affected limb is not sufficient for reducing the overall effect of disturbances due to uneven terrain. It is possible that other factors, such as changes in step height or disturbances to the intact limb, play a larger role in difficulty balancing while walking over uneven surfaces.

Legged locomotion over irregular terrains: state of the art of human and robot performance

“…The total surface was 8 m long and 1.5 m wide. Chiu et al [111] used a prosthesis emulator system to try a new controller whose aim was to reduce the effect of the disturbances caused by uneven terrains. The uneven terrain proposed to validate this new controller consisted of a treadmill with wooden rectangles placed at three different heights.…”

“…We classified the different studies involving robots according to the number of robotic legs: 18 studies focused on hexapods [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]; 32 studies focused on quadrupeds ; 34 studies focused on bipeds [4, . We also included five studies involving robotic prostheses [108][109][110][111][112]. Nine studies were grouped together and classified as 'other', such as those including salamander-like [113,114], modular [115], multi-legged [116,117], snake-like [118][119][120] and tread robots [121].…”

“…In 2021, two studies [111,112] focused their work on studying the improvements of their controllers over uneven terrains. Chiu et al [111] observed a reduction of ankle torque variability in the sagittal and frontal plane but concluded that this was not enough to overcome the disturbances produced by the terrain irregularity.…”

“…In 2021, two studies [111,112] focused their work on studying the improvements of their controllers over uneven terrains. Chiu et al [111] observed a reduction of ankle torque variability in the sagittal and frontal plane but concluded that this was not enough to overcome the disturbances produced by the terrain irregularity. Jang et al [112] concluded that their prosthesis was able to adapt to the ground in the coronal plane, maintaining stability while walking through uneven terrain.…”