Amputation at the above-knee level severely impairs the ability of an individual to ambulate. As ambulation requires power generation and active control of movements, the passive nature of most available leg prostheses is a major cause of the observed deficits. Powered prostheses aim to address this limitation using battery-operated servomotors. However, due to the wide ranges of torque and speed necessary to assist ambulation, available powered prostheses are significantly heavier than passive prostheses, which limits their effectiveness and clinical viability. In this letter, we introduce the first fully powered robotic knee prosthesis that matches the weight of state-of-the-art passive prostheses while providing suitable torque and speed to power ambulation on level ground and stairs. Dynamic simulations are shown together with an extended experimental assessment supporting the design of a new actively variable transmission. A preliminary validation is provided by an above-knee amputee subject ambulating on level-ground and stairs.

A Lightweight, Efficient Fully Powered Knee Prosthesis With Actively Variable Transmission

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

This paper proposes a novel semiactive ankle–foot orthosis (AFO) called SmartAFO equipped with an elastic link mechanism. The design of the device is based on the understanding of gait biomechanics for gait assistance against paralysis and other gait abnormalities affecting the ankle joint function. The elastic link at the core of the developed AFO is a 1-degree-of-freedom linear-motion system, capable of regulating its viscosity via a magnetorheological fluid and an electromagnetic coil. The link is also integrated with a compression spring that allows it to store and release energy based on its coil current. This design enabled a semiactive AFO that can mitigate foot slap and toe drag without adversely affecting push-off or other gait phases. We present the development of SmartAFO and the results of experiments conducted on healthy people to verify its support functions compared to a commercial AFO. The results showed that SmartAFO can provide controllable braking torque at the heel contact, avoid ankle motion obstruction during the push-off phase, and support toe lift during the swing phase.

Robotic Ankle–Foot Orthosis With a Variable Viscosity Link Using MR Fluid

Background:Hundreds of investigations examining biomechanical outcomes of various prostheses have been completed, but one question remains unanswered: how much time should an amputee be given to ac

When to biomechanically examine a lower-limb amputee: A systematic review of accommodation times.

The functional level (K level) of prosthetic users is used to choose appropriate prosthetic components, but ratings may highly subjective. A more objective and robust method to determine K level may be appealing. The aim of this study was to determine the relationship between K level determined in the clinic to K level based on real world ambulatory activity data collected by StepWatch. Twelve individuals with transtibial limb loss gave informed consent to participate. K level assessments performed in the clinic by a single treating prosthetist were compared with a calculated estimate based on seven days of real world ambulatory activity patterns using linear regression. There was good agreement between the two methods of determining K level with R 2 = 0.775 (p < 0.001). The calculated estimate of K level based on actual ambulatory activity in real world settings appears to be similar to the treating prosthetist's assessment of K level based on gait observation and patient responses in the clinic. Clinic-based ambulatory capacity in transtibial prosthetic users appears to correlate with real world ambulatory behavior in this small cohort. Determining functional level based on real world ambulatory activity may supplement clinic-based tests of functional capacity.

https://journals.sagepub.com/doi/pdf/10.1177/2055668316636316

Functional level assessment of individuals with transtibial limb loss: Evaluation in the clinical setting versus objective community ambulatory activity.

In this comparative study, three transfemoral amputee subjects were fitted with four different microprocessor-controlled exoprosthetic knee joints (MPK): C-Leg, Orion, Plie2.0, and Rel-K. In a motion analysis laboratory, objective gait measures were acquired during level walking at different velocities. Subsequent technical analyses, which involved X-ray computed tomography, identified the functional mechanisms of each device and enabled corroboration of the performance in the gait laboratory by the engineering design of the MPK. Gait measures showed that the mean increase of the maximum knee flexion angle at different walking velocities was closest in value to the unaffected contralateral knee (6.2°/m/s) with C-Leg (3.5°/m/s; Rel-K 17.0°/m/s, Orion 18.3°/m/s, and Plie2.0 28.1°/m/s). Technical analyses corroborated that only with Plie2.0 the flexion resistances were not regulated by microprocessor control at different walking velocities. The muscular effort for the initiation of the swing phase, measured by the minimum hip moment, was found to be lowest with C-Leg (-82.1±14.1 Nm; Rel-K -83.59±17.8 Nm, Orion -88.0±16.3 Nm, and Plie2.0 -91.6±16.5 Nm). Reaching the extension stop at the end of swing phase was reliably executed with both Plie2.0 and C-Leg. Abrupt terminal stance phase extension observed with Plie2.0 and Rel-K could be attributed to the absence of microprocessor control of extension resistance.

Designs and performance of microprocessor-controlled knee joints

A crossover design study with a small group of subjects was used to evaluate the performance of three microprocessor-controlled exoprosthetic knee joints (MPKs): C-Leg 4, Plie 3 and Rheo Knee 3. Given that the mechanical designs and control algorithms of the joints determine the user outcome, the influence of these inherent differences on the functional characteristics was investigated in this study. The knee joints were evaluated during level-ground walking at different velocities in a motion analysis laboratory. Additionally, technical analyses using patents, technical documentations and X-ray computed tomography (CT) for each knee joint were performed. The technical analyses showed that only C-Leg 4 and Rheo Knee 3 allow microprocessor-controlled adaptation of the joint resistances for different gait velocities. Furthermore, Plie 3 is not able to provide stance extension damping. The biomechanical results showed that only if a knee joint adapts flexion and extension resistances by the microprocessor all known advantages of MPKs can become apparent. But not all users may benefit from the examined functions: e.g. a good accommodation to fast walking speeds or comfortable stance phase flexion. Hence, a detailed comparison of user demands and performance of the designated knee joint is mandatory to ensure a maximum in user outcome.

/pdf/designs-and-performance-of-three-new-microprocessor-3k2kwdzr3f.pdf

Designs and performance of three new microprocessor-controlled knee joints.

A test device for lower limb exoprostheses has been developed at the Department of Medical Engineering of the TU Berlin which is able to apply realistic loads to prostheses. Hence, the gait simulator meets the increasing demands on functional and fatigue testing of microprocessor controlled knee joints (MPK). An exemplary comparison of two MPK was performed to prove that known differences in the functional quality of the MPK can also be demonstrated in simulator tests. Significant differences between the MPK could be found. The MPK could not be tested in their full range of function though. To enable comprehensive functional and fatigue testing, the gait simulator has to be modified to achieve higher walking velocities and step lengths.

/pdf/the-gait-simulator-for-lower-limb-exoprostheses-overview-and-3eok21bj06.pdf

The gait simulator for lower limb exoprostheses - overview and first measurements for comparison of microprocessor controlled knee joints

The prosthesis alignment is of central importance for a harmonic gait, especially for upper limb amputees. Today alignment optimization is based on static measuring and the experience of the orthopaedic technician. To objectify the alignment process a mobile gait analysis system based on 10 inertial sensors and a 6 DOF force and moment sensor was developed at the TU Berlin. The dedicated software adds dynamic gait parameters into the optimization process and guides the necessary changes in the prosthesis alignment. Therefore 19 common alignment changes were analysed based on measurements with 2 subjects fitted with the C-Leg knee. The anterior and posterior displacement of the knee will be the focus of an additional study with 6 subjects.

/pdf/a-mobile-gait-analysis-system-for-optimization-of-prosthetic-470l77d9i3.pdf

Julius Thiele

Papers

Designs and performance of microprocessor-controlled knee joints

Designs and performance of three new microprocessor-controlled knee joints.

The gait simulator for lower limb exoprostheses - overview and first measurements for comparison of microprocessor controlled knee joints

A Mobile Gait Analysis System for Optimization of Prosthetic Alignments