Goal: To provide an overview of control strategies in commercial and research microprocessor-controlled prosthetic knees (MPKs). Methods: Five commercially available MPKs described in patents, and five research MPKs reported in scientific literature were compared. Their working principles, intent recognition, and walking controller were analyzed. Speed and slope adaptability of the walking controller was considered as well. Results: Whereas commercial MPKs are mostly passive, i.e., do not inject energy in the system, and employ heuristic rule-based intent classifiers, research MPKs are all powered and often utilize machine learning algorithms for intention detection. Both commercial and research MPKs rely on finite state machine impedance controllers for walking. Yet while commercial MPKs require a prosthetist to adjust impedance settings, scientific research is focused on reducing the tunable parameter space and developing unified controllers, independent of subject anthropometrics, walking speed, and ground slope. Conclusion: The main challenges in the field of powered, active MPKs (A-MPKs) to boost commercial viability are first to demonstrate the benefit of A-MPKs compared to passive MPKs or mechanical non-microprocessor knees using biomechanical, performance-based and patient-reported metrics. Second, to evaluate control strategies and intent recognition in an uncontrolled environment, preferably outside the laboratory setting. And third, even though research MPKs favor sophisticated algorithms, to maintain the possibility of practical and comprehensible tuning of control parameters, considering optimal control cannot be known a priori. Significance: This review identifies main challenges in the development of A-MPKs, which have thus far hindered their broad availability on the market.

A Comparison of Control Strategies in Commercial and Research Knee Prostheses

Energy storing and return (ESAR) feet are generally preferred over solid ankle cushioned heel (SACH) feet by people with a lower limb amputation While ESAR feet have been shown to have only limited effect on gait economy, other functional benefits should account for this preference A simple biomechanical model suggests that enhanced gait stability and gait symmetry could prove to explain part of the difference in the subjective preference between both feet To investigate whether increased push-off power with ESAR feet increases center of mass velocity at push off and enhance intact step length and step length symmetry while preserving the margin of stability during walking in people with a transtibial prosthesis Fifteen people with a unilateral transtibial amputation walked with their prescribed ESAR foot and a SACH foot at a fixed walking speed (12 m/s) over a level walkway while kinematic and kinetic data were collected Push-off work generated by the foot, center of mass velocity, step length, step length symmetry and backward margin of stability were assessed and compared between feet Push-off work was significantly higher when using the ESAR foot compared to the SACH foot Simultaneously, center of mass velocity at toe-off was higher with ESAR compared to SACH, and intact step length and step length symmetry increased without reducing the backward margin of stability Compared to the SACH foot, the ESAR foot allowed an improvement of step length symmetry while preserving the backward margin of stability at community ambulation speed These benefits may possibly contribute to the subjective preference for ESAR feet in people with a lower limb amputation

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Energy storing and return prosthetic feet improve step length symmetry while preserving margins of stability in persons with transtibial amputation

Introduction Evaluating the efficacy of a lower-limb prosthetic device (LLPD) is a crucial step in the iterative process of redesigning and product development of new generation prostheses. To date, no standardized experimental methodology for the evaluation of LLPDs is available which complicates the comparison of results. Objective This systematic review provides an overview of study designs, tests and outcome measures to evaluate a LLPD. Ultimately, guidelines and recommendations are formulated. Methods Two databases were screened on studies evaluating a LLPD, published between 2009 and 2019. Results 109 articles were eventually included. We identified 43 outcome measures in four main categories: 53% were biomechanical, 26% physiological, 14% physical performance and 7% psychological. Mainly walking tests were included (78%), of which 31% were performed on a slope, followed by stair climbing (15%) and other functional tasks (15%). Conclusion An overview of currently used study designs and experimental protocols is presented, which led to guidelines and recommendations for the evaluation of a LLPD. The main recommendation is to include daily activities in a case-report and in a later stage in a randomized controlled study design. Biomechanical, physiological, physical performance and psychological outcome measures are key for the evaluation of a LLPD.

Guidelines and Recommendations to Investigate the Efficacy of a Lower-Limb Prosthetic Device: A Systematic Review

Background The microprocessor-controlled prosthetic knees have been introduced to transfemoral amputees due to advances in biomedical engineering. A body of scientific literature has shown that the microprocessor-controlled prosthetic knees improve the gait and functional abilities of persons with transfemoral amputation. Objective The aim of this study was to propose a new microprocessor-controlled prosthetic knee (MPK) and compare it with non-microprocessor-controlled prosthetic knees (NMPKs) under different walking speeds. Methods The microprocessor-controlled prosthetic knee (i-KNEE) with hydraulic damper was developed. The comfortable self-selected walking speeds of 12 subjects with i-KNEE and NMPK were obtained. The maximum swing flexion knee angle and gait symmetry were compared in i-KNEE and NMPK condition. Results The comfortable self-selected walking speeds of some subjects were higher with i-KNEE while some were not. There was no significant difference in comfortable self-selected walking speed between the i-KNEE and the NMPK condition (P= 0.138). The peak prosthetic knee flexion during swing in the i-KNEE condition was between sixty and seventy degree under any walking speed. In the NMPK condition, the maximum swing flexion knee angle changed significantly. And it increased with walking speed. There is no significant difference in knee kinematic symmetry when the subjects wear the i-KNEE or NMPK. Conclusions The results of this study indicated that the new microprocessor-controlled prosthetic knee was suitable for transfemoral amputees. The maximum swing flexion knee angle under different walking speeds showed different properties in the NMPK and i-KNEE condition. The i-KNEE was more adaptive to speed changes. There was little difference of comfortable self-selected walking speed between i-KNEE and NMPK condition.

The comparison of transfemoral amputees using mechanical and microprocessor- controlled prosthetic knee under different walking speeds: A randomized cross-over trial

IntroductionMicroprocessor knee analyses to date have been primarily limited to microprocessor knees as a category rather than comparisons across different models. The purpose of the current analys...

https://journals.sagepub.com/doi/pdf/10.1177/2055668320968476

M.R. Prins

Papers

The influence of a user-adaptive prosthetic knee across varying walking speeds: A randomized cross-over trial