The Design of a Smart Lower-Limb Prosthesis Supporting ...

1. Introduction

Amputation of the limb or extremity of a limb, either from the upper extremity amputation (UEA) or lower extremity amputation (LEA) of the human body, affects people&#;s quality of life. Globally in , the highest number of trauma amputations was in East and South Asia, followed by Western Europe, North Africa and the Middle East, increasing in North America and Eastern Europe [ 1 ].

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In a 28-year study (&#;) on the incidence of lower extremity amputations in 19 countries (EU15+) by Hughes et al. [ 2 ], significant geographic and temporal variability was observed. According to this study, Australia had the highest incidence of LEA in women and men during the study period. However, this incidence decreased steadily in the Netherlands and the USA, and a higher percentage reduction is found in the USA. Another recent study examined Germany&#;s LEA incidence from to [ 3 ]. According to this study, in , compared to , the incidence of major amputations decreased by 7.3%, while the incidence of minor amputations increased by 11.8%, and there was also a decrease in the incidence of women to men.

In terms of the causes that led to the amputation of the lower limbs, demographically, there are many differences between developed and developing countries. For example, compared to developed countries where most amputations are due to disease processes such as diabetes, the causes of amputations are more related to environmental factors, living conditions, or wars in developing countries [ 4 ].

Individuals who have had lower limb amputations face many other physical challenges that can compromise their health and mobility. Hence the need for a technical replacement (prosthesis) that restores the biomechanical function of the amputated element and the body&#;s integrity. Management of lower limb prostheses for these individuals is a complicated issue. Unfortunately, the candidates who want to benefit from the usefulness of a prosthesis are a heterogeneous group with distinct ages and needs. In addition, the choice of the perfect candidate depends on the following factors: the aetiology of limb loss, the level of amputation, comorbidities and health, the postoperative stage, and the state of rehabilitation. Lower limb prostheses can be classified into three types of devices: passive, semi-powered or powered. For example, individuals with transtibial amputation (the term transtibial indicates that the amputation occurred between the knee and the ankle) are usually prescribed a prosthesis for storage and return of passive elastic energy, made of carbon fibre and works as an arc without the ability to generate energy again or to articulate. Most ankle and foot prostheses available on the market until the early s were completely passive. The simplest solution for transtibial amputations is a solid prosthesis of the foot without an ankle joint [ 5 ]. As a result, the mechanical properties did not adapt to the user&#;s walking speed and terrain type. Individuals with transtibial amputation often adopt compensatory gait strategies. These can lead to significant changes in gait dynamics, the joints loading and working, and the muscular activity of the affected and unaffected leg [ 6 ]. In the last three decades, approaches in prosthetic technology have led to significant advances, especially regarding biomechanical and user comfort [ 7 ] and in walking symmetry and energy cost [ 8 ]. An excellent example of a marketable passive prosthetic foot is the C-Walk [ 9 ], equipped only with passive components but combined suitably. As a result, it is more effective from an energy point of view compared to other prostheses in this category.

The first electrically powered ankle-foot prosthesis was built in and was pneumatically operated [ 10 ]. Subsequently, from until now, studies have focused on designing and developing autonomous energy supply systems [ 11 18 ]. The main factors considered for the design of prostheses are both the mechanical properties [ 19 20 ] and the length of the prosthesis [ 21 ]. Another factor that should not be overlooked is the weight of the prosthetic components [ 22 ]. A higher weight also increases the stress on the socket&#;the residual connection of the limbs, which is one of the most critical elements in the prosthesis [ 23 ]. In addition, most studies in the literature have been conducted on the evaluation of kinematic and kinetic gait [ 24 ] and foot plantar pressure [ 25 26 ].

Magnetorheological fluids (MR) were successfully introduced into prosthetic devices after . In , a patent was published [ 27 ] for a variable torque magnetorheological knee prosthesis produced by Ossur Inc, Los Angeles, CA, USA [ 28 ]. Herr and Wilkenfeld [ 29 ], in , presented a magnetorheological knee prosthesis that automatically adjusts the cushioning of the knee to walking amputated using only local detection of the knee, torque and strength position. In , a study related to [ 27 ] was carried out, which was intended to be part of a project to create models with finite elements of the knee [ 30 ]. Another invention patent [ 31 ] was published in generally relating to powered human augmentation devices, such as lower-extremity prosthetic, orthotic, or exoskeleton apparatus, and/or humanoid robotic devices designed to emulate human biomechanics. Among the most current studies is [ 32 ], which analyzes the energy consumption of a magnetorheological active knee actuator that has been designed for transfemoral prostheses. The system was developed as an operational motor unit consisting of an EC motor, a harmonic drive, and a magnetorheological clutch (MR) parallel with an MR brake.

By analyzing the above literature, it can be said that significant advances have been made in the research and development of prostheses for the lower limbs, which has led to an increase in the function and quality of life for many people with amputations of the lower limbs living in developed countries. However, one downside of this new research and development is that many potential users live in developing countries and cannot benefit from this new technology. This fact is due to multiple causes: cost, durability, maintenance or access to these prostheses. Under these conditions, research needs to focus on designing and developing cost-effective foot prostheses that meet economic, environmental and physical standards to cope with unfavourable climates and working conditions. So far, many cheap prosthesis projects have been done to support the lower limbs, such as [ 33 35 ]. Our team aims to design and implement a low-cost prosthesis to support people with lower limb amputation (especially transtibial amputation). In the first phase, two goals were set: to design the smart ankle prosthesis and implement a solution to determine the weight distribution on the sole. The smart ankle prosthesis is intended to be developed as a passive one (from the articulation actuation point of view) and controllable (by using a magnetorheological fluid and controlling its properties to obtain a controllable damping effect inside the articulation). For the weight distribution on the sole, in this stage of our research, we will propose an alone sandal with eight pressure sensors. The first objective we set for the current study is to propose a smart ankle prosthesis design; the second objective is to design, develop, and validate a solution to determine the weight distribution on the sole; the third objective is to conduct a series of measurements which allow us to test the data acquisition system firstly and to compare the acquired data against other systems presented in the literature, and secondly to create a dataset which will be used to design a future algorithm which to detect the gait phases. With these parameters determined, it is possible to control the optimal position of the prosthesis joints, depending on the phase and the type of movement. The determinations were made for people without amputated limbs. The appropriate values for an amputated limb can be determined by mediating their values. This simplified and optimized system can be integrated into a prosthesis for its configuration in real-time, regardless of the phase or type of movement.

Our Prosthesis Design

The research effort in this field focuses on improving the characteristics of the artificial ankle to closely simulate the human ankle&#;s functionality. The design of an artificial ankle involves many scientific and technical areas such as medicine, robotics and mechatronics, biomechanics, material science, mechanical engineering, electronics, and others. The challenge of the ankle prosthesis design is to find the means to achieve the functions of an intact ankle, especially the role of power generation.

This study presents an innovative solution for a smart ankle prosthesis based on smart fluids that will simulate the functionality of the human ankle for both walking and running activities.

The mechanical structure consists of the mechanical elements of a standard prosthesis ( Figure 1 ). The innovative element will be a spherical joint based on smart fluids (class 4), which replaces the human ankle joint. The spherical joint allows two rotations, corresponding to the up and down movement and the lateral rotation of the foot. For each rotation, the spherical joint consists of two concentric hemispherical shells between which there is a magnetorheological fluid. The volume between the two spherical shells is divided in two by a fixed belt. Also, a spherical cap rotates between the two spheres. It is rigidly attached to the prosthesis elements, rotating with them and generating the rotational movement of the ankle. Angle 0 divides the fluid into two equal volumes for the relaxation position.

At the rotation between the two hemispheres, the fluid is circulated from one space to another through a magnetorheological stop valve (outside the joint). Due to the incompressibility of the fluid through the control of the stop valve, the control of the rotation of the spherical cap between the two hemispheres is obtained, so implicitly, the control of the rotation of the joint. For the second axis of rotation, proceed similarly. The joint is shown in Figure 2 . Its detailed description is presented in the works [ 36 ]. Also, the mechanical system contains the reconstruction of the leg components that have been amputated (ankle, leg, etc.).

The actuator system: The prosthesis uses elastic elements that maintain the foot&#;s position in the relaxation position. Also, the ankle joint allows rotation (lateral and vertical) under the action of body weight (support on foot, walking, running). A stop-valve controls both movements of the joint with rheological fluid. After the cessation of the effort (due to the move), the elastic elements bring the paw to the position of relaxation.

The sensorial system: The sensory system provides information about the position of the articulation of the prosthesis and the force exerted on it due to the body&#;s movement (size, direction). The information is provided to the control system. It consists of incremental rotation sensors (associated with the spherical joint) and force sensors (associated with the foot paw). In addition, the value of the working pressures for the stop valve is given by pressure sensors.

The control system: Prosthesis control systems must accomplish multiple tasks, such as recognizing the amputee&#;s intended movements (high-level control), applying an appropriate control law based on the amputee&#;s intent (mid-level control), and using local feedback to command the actuation systems within the prosthesis (low-level control). The control system will be capable of controlling the ankle joint across various ambulation modes (level-ground walking, ramp ascent/descent, stair ascent/descent, running); however, these control strategies are highly sophisticated.

There is a known ankle prosthesis that solves this problem through two constructive solutions, namely:

(1)

The most used solution is the prosthetics leg for normal daily activities (upright position, walking, etc.). Generally, they are designed strictly for one person (weight, dimensional) and a spherical joint of class 5 that allows vertical movements of the foot. Most of these prostheses are passive, and the movement control is performed (strictly mechanical) by elastic elements or hydraulic/pneumatic cylinders. These have the disadvantage of the need for design strictly reported to a beneficiary. They also allow only one type of activity (e.g., walking) [ 37 ].

(2)

Another solution is the prosthetic for particular activities (sports activities: running, jumping). They are generally built from a single elastic body without containing the rotating joint. Therefore, they are dedicated only to sports activities, designed only for certain types of requests, strictly for one person. To switch to daily activities, it is necessary for this person to change the prosthesis [ 38 ].

The classical spherical joints do not control the movement of interconnected elements, having only the role of a passive kinematic couple.

Our spherical joint based on smart fluids was proposed in a national patent application: Spherical joint based on intelligent fluids&#;A// [ 39 ] and was a gold medalist at Euro Invent .

The rest of the paper is structured as follows: Section 2 presents the design of the prosthesis and the sensory system, as well as the data validation of the sensory system; Section 3 shows the results obtained from the simulations; Section 4 presents the challenges associated with the development of such systems and their potential solutions, as well as a discussion about the future research perspectives are given; finally, Section 5 is devoted to the conclusions.

A total of 18 eligible participants were approached by letter, of whom ten agreed to participate. On the day of the focus group, two participants unfortunately cancelled. Furthermore, two participants ultimately did not meet all inclusion criteria, as one had a transtibial amputation and the other had an osseo-integration. They did participate in the focus group, but their quotes were not included in the final analysis. The group consisted of 6 male and 2 female participants. The mean age was 60.6 years old (range: 40&#;78 years; ).

The participants agreed with the seven themes of the pre-final framework but had 14 suggestions for additional factors. Since four had a clear overlap with existing factors, eventually ten factors were added to construct the final framework ( ).

Themes and factors

Theme 1: Prosthesis related

This theme contains factors related to the characteristics of the prosthesis.

Meta-synthesis

The appearance of the prosthesis was often mentioned as an important factor [19,29,33,35,37,41]. While most of the participants preferred the prosthesis to blend in and not be noticed easily, some participants did not mind about the appearance of the prosthesis as long as it was functional.

&#;After it happened to me and I had got the leg, this monstrosity of a thing with hinges and everything&#; You think oh my God look at that thing. But then you start to move and you realize that you are up and moving again. [&#;] I didn&#;t give a damn who was looking at me, I just wanted to get out and about&#;

[29]

The appearance of the prosthesis in combination with clothing was also discussed a number of times, since clothing can often conceal the physical impairment [19,29].

Participants mentioned that the wearing comfort and the fit of the prosthesis, specifically the socket, can have a great impact on their prosthesis use and satisfaction with the prosthesis [19,29&#;31,35&#;37]. It was reported that an improperly fitted prosthesis was the most common cause of stump pain [29].

&#;It is very frustrating. Sometimes you can get them and you can walk for miles and they will be grand. The next day you could put on the limb and it will start cutting you&#; It is the most annoying part.&#;

[29]

Three articles mentioned the importance of reliability and the frustration that comes with malfunctioning prostheses [29,30,33]. A malfunctioning or broken prosthesis left the users immobile and dependent on others [29].

&#;It happened to me at work one day when the knee went on it [knee buckled]. I just couldn&#;t move. Two fellas had to carry me out into another fella&#;s car to give me a lift home. The thing broke and you couldn&#;t move.&#;

[29]

The durability of the prosthesis can have an effect on a person&#;s work, activities and number of visits to the prosthetist for repairs [30,33,40]. Therefore all participants who mentioned this factor expressed an interest in durable prostheses.

Focus group

While discussing this theme, participants mentioned that reliability is an important factor to them. The prosthesis can sometimes act unpredictable or break down suddenly, which results in potential hazards and immobility for the user. Participants also mentioned that the fit of the prosthesis influences their prosthetic use and satisfaction. Fluctuations in the residual limb were mentioned as a reason for changing the fit of the prosthesis. Changes in the weather and temperature were discussed as possible explanations for these fluctuations.

&#;Everything depends on the socket. As soon as the socket doesn&#;t fit correctly, you are continually slowed down.&#;

[P3]

The participants also discussed the weight of the prosthesis. It was mentioned that the weight is not only an issue while wearing the prosthesis, but also when it is taken off.

&#;To me, the weight is not only decisive when I&#;m wearing it, but also when I&#;m not. With cleaning and things like that, I do think mine [prosthesis] is very heavy.&#;

[P3]

One of the participants also mentioned that even though the weight of the prosthesis is roughly the same as a healthy leg, it does feel heavier.

Lastly, the ability to change between multiple types of shoes, as well as the properties of the shoes were discussed, which resulted in the addition of the factor &#;shoe options&#; to the final framework. It was discussed how the weight, stiffness of the sole and height of the heel could influence the wearing comfort of the prosthesis. Furthermore, female participants expressed the desire to be able to change the heel height of their prosthesis in order to wear heels.

&#;I find it annoying that you can&#;t buy the shoes you want. They can&#;t be too slippery and I always have to do something about the heels.&#;

[P1]

Theme 2: Rehabilitation, costs and prosthetist

The theme consists of factors that are related to each aspect of rehabilitation after an amputation, receiving a prosthesis and the additional costs.

Meta-synthesis

Some participants experienced the rehabilitation program as an inadequate or insufficient resource [31]. However, the majority of the participants expressed their satisfaction about their rehabilitation program. It was a way to learn new skills and train with their prosthesis [30&#;34,36&#;39].

&#;Rehabilitation is important because it is helping me to return to my daily life and most importantly to walk again! I have hope in the prosthesis! It will help me become a different person and leave the wheelchair.&#;

[31]

Participants also had contradictory opinions about the expertise of guidance they received. Whereas some were enthusiastic about the rehabilitation staff others expressed that they felt like their prosthetist did not listen or lacked proper training [30].

&#;Rehabilitation has been very helpful for me&#; I am able to walk alone again! The staff has been lovely and I&#;m feeling like another person!&#;

[31]

Focus group

Throughout the focus group meeting, one factor that kept coming back into conversation was the health insurance procedure. Participants expressed a lot of frustration about rejections for certain prosthetic components and in one case being denied a trial period to test a specific prosthetic knee for a few weeks.

&#;Something that was missing for me was the ability to test [different components/prostheses]. I think it is essential. You can want all kinds of things, but if you notice it isn&#;t possible or it does not suit you&#;&#;

[P3]

Another participant mentioned that he was given one type of knee and had no other options.

&#;It was clear that I could just get this knee. It did not come up that anything else was possible. They [health insurer] thought I managed well enough on this mechanical knee.&#;

[P8]

Overall, the participants expressed the desire to have a clear, transparent communication between them and the rehabilitation team. The opinions about the user involvement in the process of choosing a prosthesis were mixed. Other participants did not recognise such experiences and explained that they were involved in the process by the rehabilitation team. They also felt supported in their &#;battle&#; with the health insurance company. Further along in the conversation, the importance of having a good relationship with the prosthetist was emphasized.

&#;Well, the most important thing is to have a prosthetist who understands what you need and how to go down those paths. But in addition to that, you have to have a health insurance company that grants it to you, because it&#;s just a grant-factor&#;&#;

[P5]

Something that the participants felt was missing, was available information about different types of prostheses and prosthetic components. They have to rely on the information they receive from the rehabilitation team, since the information online is very limited and subjective.

&#;I mentioned it from the beginning, you [rehabilitation team] can tell me what I need, but how am I supposed to know? I have to believe what you tell me, because there is no information available. The problem is that there&#;s not enough information to find about this [prostheses]. &#; Yes you can find a lot about the C-leg or Rheo knee, but that&#;s it.&#;

[P5]

Theme 3: Social

This theme consists of factors related to a person&#;s social relationships, their position in society and the associated reactions.

Meta-synthesis

Having a good support system in place can help prosthesis users with several aspects of life; for example: processing the amputation, dealing with finances and helping with tasks in and around the house. Receiving support from friends and family was often discussed, however not all participants specified what support they received. Friends and family mainly supported the prosthesis user with the acceptance of their situation [29&#;34,36,38].

&#;My family is the main reason for my recovery! They have been giving me a lot of support, helped me to walk again and to cope with this situation.&#;

[31]

Being able to talk to other persons with a lower limb prosthesis also had a positive influence on the participants. The presence of peer support was a good experience for the participants. Those who did not experience it during their rehabilitation phase expressed missing this, since the rehabilitation team can help but does not understand the full situation [29,32&#;34,38].

&#;I feel support groups are extremely important. Doctors and therapists are also important, but they cannot understand the frustrations an amputee goes through unless they are an amputee.&#;

[33]

Most participants mentioned a fear of getting negative reactions in public, or having experienced this in the past [19,29,31,32,34,35,39,41]. One participant mentioned being torn between wanting people to know about the prosthesis and not wanting to tell them.

&#;Yeah, but I am always more comfortable if people know. I have been in so many situations for example in pubs where people might slap my leg and say Jesus what is that. So I would be more comfortable if people knew. At the same time I don&#;t go broadcasting it.&#;

[29]

Many participants expressed a desire to fit in with other groups and be the same as others [19,29,34,35,38,39,41]. They find it hard to accept that they stand out and want to belong and &#;be normal&#;, which often means wanting to be the same as persons without lower limb loss.

&#;I can ambulate quite effectively on it and I don&#;t feel so cut-off or left out of what everybody else is doing. And that&#;s really a big thing for me, because I felt like I didn&#;t belong or that I was substandard somehow as everyone moved about freely and around me. And that was difficult to accept, it was hard on me.&#;

[41]

Focus group

At first glance, the factor &#;advertisement&#; was not clear to all participants. Even after a further explanation, one of the participants still did not relate having any influence on his prosthesis use or satisfaction to this factor. Others mentioned that the information on the internet was often focussed on the more expensive prostheses.

&#;When you are looking for information, you only find the very expensive prostheses to which the health insurance companies say no.&#;

[P5]

Subsequently, the participants discussed the different reactions they get from others in public. The experiences varied from positive to negative experiences.

&#;I&#;m in shops more often now and often I have the mobility scooter with me, because I can&#;t walk a good distance yet. I notice that people find me very annoying, or I&#;m too slow, or you hear a sigh&#;I find it difficult.&#;

[P3]

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Anonymity was a topic that was shortly discussed and the opinions varied. Whereas a few participants did not mind showing their prosthesis in public, others did not feel comfortable doing so and preferred not to be noticed.

&#;Other people just walk around without any clothes on [covering the prosthesis] and have no problem with that; I don&#;t have that (or I don&#;t feel that way). The sound [of the prosthesis] was also annoying to me. Basically I just want to be unobtrusive.&#;

[P1]

Most participants also mentioned a variety of reactions they had received from friends and family, ranging from prejudice about their abilities to problems with acceptance. This could sometimes lead to unwanted help and frustrations. One participant mentioned that it sometimes felt like his family had a harder time accepting his amputation than he did. Since the participants felt that these experiences did not fit in any of the factors on the pre-final framework, the factor &#;reactions from friends/family&#; was added.

Wearing a prosthesis can have an effect on someone&#;s ability to perform specific roles, such as being a parent.

&#;When my daughter was born, I was like: you can&#;t walk around with this [prosthesis] anymore. You can&#;t hold a baby and risk collapsing. So then I got a C-leg and I am very happy with it.&#;

[P1]

It can also influence the way they interact with their loved ones.

&#;I feel like a different person when I&#;m wearing a prosthesis. It may sound a bit crazy, but I feel more complete when I am standing up. Life is so much more fun standing up. Being able to hug your husband or looking someone in the eyes.&#;

[P3]

Lastly, one participant noticed the absence of the factor &#;sexuality&#;. Other participants agreed that this was an important factor, but it was not discussed any further. Therefore, &#;sexuality&#; was added to the final framework.

Theme 4: Activities and participation

Factors included in this theme are related to a person&#;s personal tasks and activities, as well as their participation in society.

Meta-synthesis

Being able to participate in leisure activities, such as sports, are often mentioned as a positive influence on participants&#; life [29,31,32,34&#;36,38&#;40]. Furthermore, the use of a prosthesis can help with other aspects as well, like returning to school or work and self-care [29&#;32,34&#;36,38&#;40].

&#;Today I&#;m a new person! I returned to school and to work! I bodyboard! My life is not the same but it [amputation and prosthesis] is already a part of me! I adjusted my life to it, but I haven&#;t stopped doing my favourite hobbies or meeting my friends.&#;

[31]

Participants also discussed the fact that the use of a prosthesis can sometimes force them to prioritize certain activities over others, in order to preserve their energy or because of discomfort [32,34&#;36].

&#;First of all, you [do] less activities than you would normally because, say like you planned to go to the mall or you planned to go to the beach or something and you are having a bad day or in pain with your stump. Of course you wouldn&#;t do it that day and you would be a little grouchy, you know, because the pain is irritating and you would be less active in your normal day.&#;

[36]

Focus group

One of the participants mentioned that he felt that the rehabilitation team and prosthetist should pay more attention to leisure activities. Other participants agreed with this statement and spoke up about the desire to partake in sports. Some of them felt held back by the rehabilitation team, since they were told they could no longer do certain sports or would have to rely on a wheelchair to do so.

&#;What I miss very much about this is that, in practice, hobbies are not considered at all. In fact, I want to do a lot of sport, but in my case they said, yes, do that in a wheelchair. So I do indeed miss that, if you want to, you just don&#;t get the opportunity. That hobbies are looked at&#;I think as a luxury&#;

[P3]

Prioritizing activities was something all participants agreed on. Due to the use of the prosthesis, they had to make decisions about which activities they could or could not do. The main concern was running out of energy faster.

&#;If I choose to go for a walk, just to train myself, then that is a choice. I will put my energy into that and afterwards I need some time to recover.&#;

[P1]

Overall, most of the participants agreed that they shared the desire to be able to do things the way they used to before their amputation.

&#;I want to be able to do the things I would normally do [before amputation] with my prosthesis. I want to be able to walk a bit faster with my children and just do my daily things in a normal way.&#;

[P5]

Theme 5: Physical

This theme includes all factors that are related to the body of the prosthesis user.

Meta-synthesis

Participants had mixed opinions about the physical abilities and restrictions that are connected to prosthesis use. While some where happy to be able to walk and have some mobility, others highlighted some physical restrictions they experienced as limitations such as not being able to walk up the stairs or to run.

&#;My biggest problem was teaching my daughters about riding a bike and running alongside them for a long distance &#; I could run a few feet, but wasn&#;t running a block or anything like that.&#;

[36]

The occurrence of skin irritation was a problem for many prosthesis users [29,33&#;37]. One participant acknowledged some limitations, but opted not to focus on these:

&#;Yes, there are limitations, even though I choose not to focus on them. I don&#;t have the same endurance I once did. I can&#;t run as fast as I would with a real leg. Sometimes, I still get blisters, or lose my balance. But I look at it from the perspective that everybody has bad days. Everyone sits down and cries once in a while. And that&#;s okay.&#;

[35]

Focus group

One of the first things that was mentioned when this theme was discussed was the factor &#;gender&#;. At first it was not clear to all participants what this factor entailed, but two participants described gender-specific problems they experienced while using their prosthesis. For women this entailed having to cope with menstruation. For men the experience of getting one&#;s testicles stuck in the brim of their socket was discussed as a negative gender-specific problem.

The next topic that was discussed, was the sensibility of the stump. Scenario&#;s that normally would not hurt, suddenly felt excruciating. Since this topic did not fit any of the existing factors, &#;stump sensibility&#; was added.

&#;The other day when I was running the fan in the summer, it felt like my whole leg was on fire.&#;

[P5]

In addition to stump sensibility, skin irritation was discussed as an issue that can have an impact on the prosthesis use.

&#;I&#;ve been walking with a prosthesis for 40 years and since a few years I have had problems with my skin. It was never an issue, but now it is and it bothers me. I can no longer walk as much as I want.&#;

[P1]

Subsequently, the participants explained that the factor &#;phantom sensations&#; was missing from the overview, since this was very different from phantom pain. Therefore, &#;phantom sensations&#; was added to the final framework.

Theme 6: Mental

The factors in this theme are all related to the prosthesis user&#;s thoughts and feelings.

Meta-synthesis

Regaining independence after amputation and not having to rely on the help of others was an often recurring factor of interest [19,29&#;34,38,39]. One study mentioned that independence should not be observed solely as a functional outcome, since it also is related to psychological aspects.

One participant explained the effect of being dependent on others:

&#;I can&#;t accept this situation because it&#;s revolting being like this&#; without driving, walking, working&#; it&#;s very sad depending on others. &#;

[31]

Undergoing an amputation and becoming dependent on others can also have an impact on someone&#;s self-image.

Today I can&#;t do many things, I became more dependent on others, with less autonomy and I changed myself! Today I&#;m a more nervous and explosive person&#; I liked reading and today I don&#;t&#; many things changed for me.

[31]

The use of a prosthesis can have a positive effect on a person&#;s independence.

&#;Until I started using the prosthesis, I was more dependent on others&#; However I still need a lot of help.&#;

[31]

The last factor that was mentioned several times, was the importance of having a positive attitude [19,29&#;33,35,36].

&#;First, you must have a good attitude, otherwise, you won&#;t use the device. We should do the best with what we&#;ve got and have faith.&#;

[30]

For some it was hard to have a positive attitude, since they had a hard time coping with- and accepting their amputation and prosthesis use [29&#;35,37&#;39]. On the other hand, there were also participants who had accepted that even though they might no longer be able to do everything, they were at least going to try.

&#;If I was given a challenge I would try anything, I would never say no I can&#;t do that or I won&#;t do that. I would try it to the best of my ability, if I can do it I will do it, if I can&#;t, I can&#;t. I will try it and maybe I can&#;t go this far, it might be only to go that far but at least I will try it.&#;

[32]

Focus group

The factor &#;need for prosthesis&#; was discussed first and most participants agreed that while they technically could do without their prosthesis, they felt less comfortable if they did not wear it.

&#;Still, I think it&#;s an interesting point, because if I don&#;t put it on one day because it bothers me too much [stump sensibility], then I don&#;t like it. Then I think that, um, not only does it make it harder to move around the house, but it just bothers me. So yes, in that sense, I can&#;t do without them.&#;

[P1]

Finally, a participant mentioned that a number of emotions was already represented in the overview, but that he missed the factor &#;emotions&#;. Other participants agreed that this theme should include emotions.

&#;Sometimes I get extremely annoyed about my leg and that actually just makes it worse&#; (Angry emotions).&#;

[P8]

Theme 7: Walking

This theme consists of factors related to walking with a lower limb prosthesis.

Meta-synthesis

Fear of falling was the most often mentioned factor and a lot of participants mentioned that this fear influenced their daily life activities [19,29,30,34,36,39]. They were aware of the fact that if they did fall, it would have a large impact on their health and mobility. Participants also mentioned that they always have to focus on the surface they walk on, as this is more difficult when using a prosthesis [30,36,40].

&#;My first priority is always know where I&#;m stepping. [Amputees] tend to walk a little slower and damn straight. If we don&#;t, we find [we fall] more often than we like to claim.&#;

[36]

Focus group

Due to the focus group, four factors were added to the theme &#;Walking&#; in the final framework. One participant immediately noticed that walking distance was missing. Other participants agreed that it should be added. The next factor that was discussed was running and the need for a special sports prosthesis. One participant mentioned he ran on his regular prosthesis once.

A following factor was &#;steps&#;; the ability to go up or down small obstacles or stairs. The researcher asked whether this was the same as the walking surface, but participants said it was a different factor and it should be part of the final framework.

&#;To me, it is essential to be able to go up and down steps while walking.&#;

[P3]

Subsequently the participants discussed natural movements and walking confidence. Even though a few participants mentioned that a natural looking gait was important to them, one participant said walking confidence was more important to her.

&#;When you are confident when you walk, it doesn&#;t matter if you can walk very neatly or with a limp. As long as you feel good (about it).&#;

[P5]

Fear of falling was something that was an issue for a few of the participants. One of them expressed he constantly had to focus not to fall while walking.

&#;I would like for once to be able to walk without having to focus all the time; without a fear of falling.&#;

[P8]

The final factor that was added to this theme, was the (in-)ability to walk backwards.

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