Increased of stability and security in transfemoral amputees with a knee-ankle synergistic system

Uneven ground, slopes, stairs, sidewalks are constraining situations that must be overcome by transfemoral amputees (TFA). However, most of prosthetic systems do not have ankle mobility, the connection between the prosthetic knee and the prosthetic foot being a rigid part. A certain flexibility is allowed by the energy storage restitution feet thanks to their stiffness. But they do not allow a complete adaptation to daily encountered walking situations, like walking on slopes (ascent and descent) or downstairs [1]. Furthermore, TFA have a high risk of falling, with more than 50% of them reporting falling at least once in a year [2]. This risk is increased by the lack of musculature due to the amputation and the lack of mobility of the prosthetic ankle during the swing phase [3]. The aim of this study was to evaluate whether a microprocessor-controlled knee-ankle system (MPK_NEW) can help improve walking in transfemoral amputees. Eleven TFA with an activity level of d4602 (International Classification of Function, Disability and Health) or higher and wearing a microprocessor knee able to control stance and swing phases (MPK_HAB), for at least 3 months, were included in this study. They wore both prostheses (MPK_HAB and MPK_NEW) for 4 weeks, starting randomly with one or the other. At the end of each period, a quantified gait analysis (level ground, 12% slopes ascent and descent, downstairs) was performed using VICON® optoelectronic system (Vicon Motion Systems, Oxford Metrics, UK, sampling at 100 Hz) with 54 full-body markers-set. Flat Foot Time (FFT, where the ankle angle in the sagittal plane was within ± 1.25° of its orientation at 20% of the gait cycle) and Minimum Toe Clearance (MTC, minimum distance between the foot and the ground during the swing phase) were calculated for both prostheses. Student or Wilcoxon test were performed to assess significance at 0.05. Fig. 1 A shows an increase in flat-foot time for all walking situations with the MPK_NEW prosthesis, which was significant (*,p_value < 0.01) for all situations but the slope ascent one. Fig. 1B shows a significant increase in MTC (*, p_value < 0.01) when walking at level ground and ascent slope with the MPK_NEW prosthesis. Fig. 1. Comparison of FFT and MTC for each prosthesis in different walking situationsDownload : Download high-res image (58KB)Download : Download full-size image The knee-ankle synergy allows plantar and dorsal flexion during the stance and swing phases, increasing FFT (stance stability) and MTC (swing phase security) in various daily situations. This was consistent with the literature observed on transtibial amputees and approaching the behavior of asymptomatic subjects [4–6]. Thus, this new prosthetic system may improve stability and security for TFA [4,7], allowing them to better adapt to their daily environment.