Biomechanic and Energetic Effects of a Quasi-Passive Artificial Gastrocnemius on Transtibial Amputee Gait

Abstract

State-of-the-art transtibial prostheses provide only ankle joint actuation and thus do not provide the biarticular function of the amputated gastrocnemius muscle. We develop a prosthesis that actuates both knee and ankle joints and then evaluate the incremental effects of this prosthesis as compared to ankle actuation alone. The prosthesis employs a quasi-passive clutched-spring knee orthosis, approximating the largely isometric behavior of the biological gastrocnemius, and utilizes a commercial powered ankle-foot prosthesis for ankle joint functionality. Two participants with unilateral transtibial amputation walk with this prosthesis on an instrumented treadmill, while motion, force, and metabolic data are collected. Data are analyzed to determine differences between the biarticular condition with the activation of the knee orthosis and the monoarticular condition with the orthosis behaving as a free-joint. As hypothesized, the biarticular system is shown to reduce both affected-side knee and hip moment impulse and positive mechanical work in both participants during the late stance knee flexion phase of walking, compared to the monoarticular condition. The metabolic cost of walking is also reduced for both participants. These very preliminary results suggest that biarticular functionality may provide benefits beyond even those of the most advanced monoarticular prostheses.

Development and Evaluation of a Powered Artificial Gastrocnemius for Transtibial Amputee Gait

“…Researchers have since attempted to isolate the incremental influence of the AG on metabolism and kinetic measures by comparing an AG-PAFP combination to a PAFP-only condition with identical mass distribution. This study provided preliminary evidence that the inclusion of the AG may, in fact, improve metabolism and influence several kinetic measures, compared to the PAFP-only condition [11].…”

“…Such an active device can provide positive net work, unlike previous quasi-passive counterparts [10,11]. If this net robotic work replaces positive muscle work, we expect to see large reductions in metabolism with the biarticular conditions, as compared to the monoarticular conditions.…”

A Robotic Emulator for the Systematic Exploration of Transtibial Biarticular Prosthesis Designs

“…Recent research has begun to investigate the potential of assistive devices that integrate ankle prostheses with knee-assistance mechanisms, herein referred to as biarticular prostheses (BPs). A range of designs has emerged, encompassing both passive and powered ankle prostheses as well as quasi-passive and powered knee exoskeletons or exosuits [17][18][19][20][21][22], While some preliminary studies report encouraging outcomes, such as enhanced metabolic walking economy and reduced hip compensations [18,19,23], BPs are not currently available for clinical use. In summary, BPs represent an emerging area of research, and additional studies are needed to explore basic questions about their design, control, and potential to improve walking outcomes in PwTA.…”

Lower-limb amputees can reduce the energy cost of walking when assisted by an Active Pelvis Orthosis

“…Exoskeleton solutions on the other hand, have rarely been explored in applications related to amputees gait assistance [8], [9]. Thus far, the assistance of a quasi-passive knee orthosis coupled to a powered ankle prosthesis has been shown to account for 3-5% metabolic reduction in two transtibial amputees [10]. In [6], the authors have hypothesized that, since hip and ankle equally contribute to the average positive power produced by the lower limb throughout the stride [11], hip exoskeletons could outperform active prostheses in improving locomotion efficiency of transfemoral amputees, given their proximal weight distribution; in that study a unilateral hip device was shown to lower the Physiological Cost Index (PCI) in one transfemoral amputee.…”