A wide variety of prosthetic feet are available to meet the diverse needs of lower-limb prosthesis users.1 Advances in materials science, motors, actuators, sensors, and computerized control systems have led to an increase in the number and variety of foot designs on the market. Prosthetic feet now often feature a variety of potentially beneficial characteristics ranging from energy storage to multiaxial articulation to external power. However, as the number of prosthetic foot options increases, clinicians and researchers are increasingly challenged to assess important differences between feet and build the evidence base needed to guide prescription practices. One potential reason for such challenges is that methods of measurement used to evaluate user outcomes, whether in clinical practice or in research studies, are often selected based on factors of importance to the prosthetist or researcher performing the assessment.
Prosthetic foot comparative effectiveness studies, for example, often include measurement of spatiotemporal,2 kinematic,3,4 kinetic,5 and energetic2,4,6,7 aspects of gait. Many of these assessment methods do not show definitive differences between types of feet, especially in comparisons that include feet with similar characteristics or designs (e.g., different types of carbon-fiber energy-storing feet).8,9 Discrepancies between these biomechanical or physiological outcomes and user perceptions (as measured via self-report or interview methods) highlight the need to reassess research methods and/or constructs of interest in these types of studies.10 Efforts to increase the ecological validity of outcomes selected for comparative effectiveness studies have led to increased use of community-based assessments3,11–13 and self-report outcome measures.13–16 However, these instruments are still often selected by prosthetists or researchers to measure outcomes they deem to be important (e.g., daily activity or mobility) rather than those outcomes that might matter to users. Such a point is relevant, as outcomes of importance identified by users and prosthetists have been shown to differ.17
Qualitative research methods are increasingly employed to help researchers identify outcomes that matter to patients and users.17–19 For example, Schaffalitzky et al.17 engaged prosthesis users and providers to explore important aspects of the prosthetic prescription. Qualitative methods, however, have not yet been used to assess outcomes of importance that may be related to specific prosthetic components, such as prosthetic feet. The purpose of this pilot study was therefore to explore outcomes that matter to prosthesis users who have experience using two different types of prosthetic feet (i.e., an energy-storing foot like the Össur Talux, and a crossover foot like the Össur Cheetah Xplore) using focus group methods and develop a model for subsequent studies. For this study, we defined outcome as a change experienced by a prosthesis user that is attributed to a prosthetic foot intervention.20 A secondary goal was to determine if common or shared experiences described by focus group participants could be used to guide selection of outcome measures suited to assessing the relative effectiveness of prosthetic feet.
A pilot focus group study was conducted to examine how lower-limb prosthesis users experienced wearing different types of prosthetic feet and explore the outcomes users identified as important. People who had used both energy-storing feet (ESF) and crossover feet (XF) in their prosthesis(es) were invited to participate in the focus group. Individuals with experience using these types of feet were invited because a recent study showed that XF users reported a number of significantly improved health outcomes, but demonstrated few changes in performance.13 Thus, we were interested in further exploring outcomes of interest for XF users through qualitative methods that allow for an inductive approach to outcome identification and measurement selection.
Volunteers were recruited from a local prosthetics clinic. Eligibility criteria included 18 years of age or older, unilateral or bilateral lower-limb amputation, at least 1 year experience using a prosthesis, and prior experience with both ESF and XF. Maximum variation purposive sampling was used to identify people who share the phenomenon of interest (ESF and XF use) but vary by other characteristics, such as age, sex, and time wearing a prosthesis. A heterogeneous sample allows for a wide range of perspectives, provides greater insight into the phenomenon, and allows for identification of information-rich cases for the most effective use of limited resources.21 All study procedures were reviewed and approved by a University of Washington institutional review board. All participants were provided with a written information statement and individuals provided informed oral consent. A brief survey was administered before participating in the focus group. The survey included questions related to demographics, health history, and prosthesis use. Survey responses were used to characterize the study sample. Pseudonyms were used in reporting participant statements to maintain anonymity.
A one-time, in-person focus group was conducted. A series of open-ended guiding questions (Table 1) were developed to prompt discussion about prosthetic feet and outcomes most important to lower-limb prosthesis users. Conversation was facilitated though relevant probing follow-up questions. Participants were given guiding questions in advance of the focus group to promote reflection.
The focus group was conducted in-person with four researchers present (i.e., two prosthetist/orthotists a bioengineer, and a prosthetic and orthotic student). One researcher (i.e., a prosthetist/orthotist with formal qualitative research training) moderated the focus group. The focus group protocol22 and guiding questions23 were developed a priori to ensure equal participation and productive group dynamics. The moderator provided introductions and ground rules for conduct, facilitated individual participation, and promoted a focused discussion.22 The other researchers recorded field notes and asked follow-up questions. Several team members had prior experience and training to conduct focus groups of people with lower-limb loss for instrument development.24 Interviews were transcribed by a communications access real-time transcription (CART) reporter to capture word-for-word group dialogue for subsequent analysis.
This study was based in a phenomenological theoretical framework. Phenomenology is the study of the lived experience of a phenomenon through interaction with those who experience it first-hand.25 Identification of a guiding theory such as phenomenology is necessary in qualitative research to provide context to study design, question development, and analyses.26 This study was conducted to examine the lived experience of people with lower-limb amputation who had used two different types of prosthetic feet. In focusing on this specific phenomenon, we applied a rehabilitation lens during study development, conduct, and analyses. Our methodology and analyses were conducted with the purpose of understanding the phenomenon of using two different types of prosthetic feet from the perspective of people with lower-limb amputation.
In addition to a foundation in phenomenology, an adapted grounded theory approach was used for analysis. We did not attempt to develop a theory,27 but rather we applied the systematic data analysis approach of grounded theory to explore the lived experience of using two different types of prosthetic feet. We also followed the systematic coding procedures (e.g., open, axial, and selective coding) commonly used in grounded theory data analysis to maximize reliability in theme development.28
Line-by-line, open coding of the focus group transcript was first performed independently by two researchers (i.e., a prosthetist/orthotist and prosthetics and orthotics student) to develop initial codes. Researchers then met to discuss and reach consensus on the initial codes. Any coding disagreements were arbitrated by a third researcher (i.e., a prosthetist/orthotist). Axial coding and inductive reasoning were then used to identify themes. Inductively arrived at themes were double-checked against study data. Finally, selective coding was used to locate the central themes of the study. Definitions for central themes were developed through consensus of the research team. The central themes were then diagrammed to explore relationships and thematic interactions of the central phenomenon (i.e., the lived experience of using two different types of prosthetic feet). Participant statements were lastly identified to support the central themes and thematic interactions. All coding procedures were performed using Atlas.ti (Berlin, Germany) qualitative software.
Seven participants were recruited for this study; however, two were unable to attend on the specified date. Five participants with lower-limb amputation (4 males/1 female), aged 41 to 59 years (mean age, 45.6 ± 7.7 years), participated in the focus group (Table 2). Three participants had unilateral transtibial amputations. One participant had bilateral transtibial amputations, and another had bilateral involvement with a transtibial and a partial foot amputation. All participants reported daily use of a prosthesis (mean, 15.2 ± 1.1 hours). Self-reported mobility via the Prosthetic Limb Users Survey of Mobility (PLUS-M)29,30 among participants (mean T-score 58.5 ± 6.3) was above average (i.e., 50.0 for people with lower-limb amputation in the PLUS-M development sample).
The following narrative describes the results of this research, detailed through the experiences participants shared during our focus group. Prosthesis users in our focus group identified three key areas related to outcomes: direct outcomes, external influences, and indirect outcomes (Figure 1, Table 3). Direct outcomes were defined as experiences immediately attributable to prosthetic foot design. External influences were relationships participants described that influenced their outcomes but were not directly related to design of the prosthetic foot. Finally, indirect outcomes were experiences that resulted from interactions or combinations of direct outcomes and external influences.
Participants in our study were asked to reflect upon their experiences wearing ESF and XF to identify functional differences between the feet. All participants in this study had previously worn ESF and were using XF at the time of the focus group. Functional improvements reported by participants in balance, gait quality, and naturalness of sensation and movement were described as factors that subsequently led to lifestyle and quality of life improvements.
BALANCE AND STABILITY
The theme of balance and stability was defined as the ability to maintain an upright, controlled posture while standing and walking. All participants identified balance and stability as foundational components for their gait and mobility. Participants in this focus group emphasized the value of standing still with less effort with XF.
“When you talk about the stability, where I noticed it the most is standing still. The old one [ESF] when you stand up, I always feel like it would take me so long to get my bearings… this one [XF] allows me to stand still better, because I’m not constantly searching for that balance.” Geoff
In addition, participants described the relief they felt when they no longer had to compensate for diminished stability in their prosthesis compared with a natural limb. Many participants emphasized the reduction in muscular work required of both their sound and residual limbs during standing in XF.
“The first thing I noticed when I stood up for the first time [with the XF] was it almost felt like there was a platform under my whole foot…. I didn’t have to balance and use every muscle in my body.” Carrie
“It’s not like planting my foot down and having to…use that calf muscle to hold myself from moving one way or the other. The foot [XF] itself allows that give, so I’m not working so hard. My leg and my calf are not working so hard. The foot itself is working.” William
As William and Carrie describe, participants reported that XF reduced their need to compensate with the unaffected limb. When asked to explain this experience, participants described a relationship between flexibility or dynamic movement of XF and a sense of uniform contact with the plantar surface of the prosthetic foot that resulted in a unique feeling of stability.
“The other one [ESF], you know, any time you move, you are on your toe or on your heel, and this one [XF], because of the flex in it, my foot stays planted on the floor, so it really—that really is a big benefit to me.” Geoff
“Before when I had my first prosthesis, I didn’t feel balanced. Like you [Geoff] said, [it’s] the heel-toe action. Because there’s so much give in the [XF], you know, like you said, it’s really stable.” William
“So, when I first put the [XF] legs on, it felt like there was a platform underneath my foot, and it was almost like a diving board, I felt really stable. But then it felt kind of bouncy, like a trampoline, once I did take a step, and after the first five steps I started crying in front of my prosthetist because I knew they [XF] were going to change my life.” Carrie
Beyond standing, participants described how their prostheses provided safety during basic mobility tasks such as navigating obstacles in the community, varying walking speed, and adapting to environmental changes. This improved sense of safety while using XF contributed to an increased sense of confidence during basic mobility tasks.
“I guess that enhancement that [Ben] is talking about is the confidence for me of making me feel more sure of myself, you know, that stability under my feet.” Carrie
“I wouldn’t take a shower unless my wife was home, just because of the…fear is the best thing I can say, of not being stable, and it [XF] takes that away.” Geoff
Improved balance and stability both in standing and walking were foundational outcomes of importance to participants in our study. Improved balance and stability were generally described as benefits first perceived by users as they wore XF. XF then often facilitated changes in other aspects of mobility, including endurance and sustained gait quality.
ENDURANCE AND SUSTAINED GAIT QUALITY
The theme endurance and sustained gait quality was defined as the ability to maintain activity over a prolonged period without excessive fatigue or degradation of walking performance. Participants in this study emphasized not only the ability to be active for longer but to do so with a normal, symmetric walking pattern. They described the challenges of maintaining gait quality when they became tired at the end of a long day.
“When I get tired and cross that line of too many steps [with ESF], I just can’t even keep my gait together. I mean, it goes into kind of a stumble. I mean, I’m not stumbling, but you can tell I have a prosthetic.” Roy
Roy and other participants expressed how XF allowed them to maintain higher gait quality throughout the day because it reduced their overall fatigue. In addition to improved gait quality throughout the day, participants described how this gait quality also contributed to the balance and stability discussed previously.
“And being tired at the end of the day, my knees would kind of roll in, as a bilateral, just to kind of hold myself up, because I was so tired by the end of the day [with ESF], and I have a tendency not to do that anymore [with XF]. I just walk straight and I can think about my hips and not think about balance as much.” Carrie
“It used to be [with ESF] my leg just felt like mush at the end of the day. When it gets that tired you feel like your leg is loose, it just feels like I almost have no control of the other one [ESF]. And with this [XF], I last longer during the day…it gives me more stability.” Geoff
Participants emphasized the importance of their gait patterns both for safety and to prevent unwanted attention. Endurance and sustained gait quality appeared to contribute to a sense of naturalness, due to the ability to maintain an optimized gait pattern throughout the day.
The theme naturalness was defined as the degree to which a prosthesis can mimic a natural limb in motion and provide sensory feedback. Participants described multiple aspects of the experience of naturalness with a prosthesis.
“Out of the four prosthesis I have ever worn, it [XF] feels like a natural foot to me sort of.” Carrie
For some, naturalness was experienced through sensory feedback and the implication that the XF could better “feel” the ground. Carrie, who has bilateral transtibial amputations and is also legally blind, emphasized the importance of this sensation.
“I think because there’s more feedback with the [XF]. You’re able to perceive what you’re stepping on, and so it tells your brain what to do…to be able to react in a different way by having that sensation and that feedback being sent to you, at least for me as a person who relies on feel, would be huge.” Carrie
Others described how both sensation and movement of the foot contributed to a more natural gait.
“I remember when I first put it [XF] on, I got in my car and I sat down. When I put my foot on the floor board, it almost felt like I felt my toes. It kind of blew my mind, because it was just like I got that sensation… I just feel like it’s a lot smoother [than my ESF]. The action, I like the action…heel-toe. It’s just kind of a roll. It’s more natural on the gait.” Roy
Participants also described a normalcy in weight distribution, flexibility, and energy return when using XF. Collectively, these characteristics contributed to a perceived reduction in the effort required to walk.
“But when I pick up my [XF] foot, the weight distribution is so wonderful. It just—my foot doesn’t feel heavier than the rest of my leg, and it picks up just like my leg would have before.” Carrie
“The foot [XF] itself allows that give, so I’m not working so hard. The foot itself is working. That platform is allowing me to walk…with normalcy, instead of putting all my effort into walking.” William
Participants described direct benefits of the XF design and identified those most important in their daily lives. Benefits related to balance and stability, endurance and sustained gait quality, and naturalness were shared among our participants, and seemed to be linked directly to the design of the foot (i.e., the extended carbon-fiber keel and posterior attachment).13 In addition to these foot-related outcomes, participants emphasized the importance of factors outside the prosthesis that positively influenced their outcomes.
In addition to benefits related to prosthetic foot design, participants discussed external influences (i.e., relationships with peers or prosthetists) and the role they played in positively influencing their outcomes. Because all participants in this study received care at the same clinic, and from the same prosthetist, they shared similar experiences interacting with peers and their prosthetist.
Participants expressed appreciation for opportunities to share experiences and learn from others with lower-limb amputation.
“Just being in that environment with all of those other amputees in [my prosthetist’s] office is major.” William
“But the only way I learned anything was sitting in [my prosthetist’s] office—on the couch there. And people said, ‘Do this, do that, do that. You got other people sitting on the couches that you can talk to, and, you know, How do you do this? How do you do that?’ Especially when you are new, you have no idea.” Geoff
In addition to learning techniques and tips for adjusting to life with lower-limb amputation, participants described how interactions with other prosthesis users inspired confidence and a newfound appreciation of their own potential.
“And I think just seeing what other people can do and have the ability to do sells itself.” Ben
“If you were to look at some of the videos [on the prosthetist’s website] and just kind of compare what life is for some and what life can be, what’'s possible. If you can see something as possible in somebody else, then, you know, like [Ben] said, it sells itself.” William
Participants emphasized the importance of their prosthetist, the patient-prosthetist relationship, and having confidence in the prosthetist’s skills. In addition to the many positive outcomes attributed to the foot design, participants acknowledged the prosthetist’s role in creating an optimal device and working with each patient to achieve positive patient outcomes.
“It's the prosthetist. It’s truly a relationship…. It’s the relationship that you have to be able to explain what you’re feeling and how things are fit, so I think that’s far more critical than equipment.” Ben
Participants’ confidence in their prosthetist was often closely coupled with the prosthesis, and confidence they developed in themselves.
“Part of it is also just going in to [my prosthetist’s] office, I met other officers, [wounded] warrior military guys that, you know, he does for softball. You know, there’s a confidence behind his leg just the minute you’re there. He’s got confidence. Psychologically, what can’t you do? I mean, it's not just the leg.” Roy
“And your possibilities are endless if that’s what you want them to be, you know, and that’s to me, that's what [my prosthetist’s] office does.” William
Participants also described how confidence in the prosthetist translated to increased confidence in their prosthesis, themselves, and their ability to try new activities and expand their mobility.
Participants lastly described outcomes that resulted from a combination of direct outcomes (e.g., improved balance associated with the prosthetic foot design) and external influences (e.g., interaction with peer users). These indirect outcomes were interrelated and included increased confidence and subsequent expanded mobility.
The theme increased confidence was defined as enhanced trust in one’s prosthesis and one’s own ability to try new activities. Increased confidence in their prostheses generally resulted from feelings of improved balance and stability, increased endurance and sustained gait quality, and greater naturalness in movement and sensation provided by the foot. Increased confidence to try new activities typically resulted from characteristics of the prosthesis and the effect of external influences such as relationships with peers and the prosthetist.
“It’s stability. Just the stability. We were talking about the [XF] base. The solid base is so comforting.” Geoff
“I mean, just regular activities, like everybody’s been saying …you don’t have to worry so much about what’s under your foot, because you can trust it [XF]. You feel like you can trust what’s under your foot and go for just about anything.” Roy
All participants described increased confidence, both in the XF itself and in themselves and their own abilities. As users’ confidence increased, so did their willingness to try new activities and push their own boundaries.
“I feel like it [XF] gives me more confidence to be able to do the things that maybe I wouldn’t have thought of before.” Carrie
“For me it's the confidence to do those things is just so reassuring that you don’t mind trying stuff. I mean, so many things that you try first, you’re so trepid… and this [XF] just changes that. You don’t have that trepidation going into trying something new.” Geoff
Increased confidence then translated into changes in perceived ability and lifestyle choices characterized by a complex relationship between confidence and expanded mobility.
A combination of increased confidence, improved functional outcomes, and interactions with peers and the prosthetist led to an overall expansion of users’ mobility. The theme expanded mobility was defined as an increase in the diversity and type of activities in which one engages. For some participants, expanded mobility meant trying new sports or recreational activities (e.g., dancing). For others, expanded mobility meant needing fewer breaks during the day at work or allowing them to do activities they had previously avoided (e.g., walking on steep hills). Participants reported increased willingness to try new activities, as well as a sense of limitless potential.
“That confidence is what pushed the drive to do it [try new things]. I would have second-guessed it or I would have tried to figure out another way other than—other than doing it myself. So yeah, it’s the foot [XF] itself that gives that confidence to go ahead and try those things, for me.” William
“I don’t know if I would have thought about that before, without the [XF] legs. I was too nervous [with ESF] …that would have been too much for me kind of thing. And now I feel like my—I don’t have any limitations. Like the sky’s the limit for me with my [XF] legs and what I’m able to do.” Carrie
Expanded mobility was characterized by some participants as their ability to complete their vocational tasks with improved efficiency, endurance, and confidence.
“I find my mobility is dramatically changed. I’m a police officer. I know I’m more efficient and I’m actually faster [in the XF] when I run than I am in a more traditional leg [ESF], and I think the ability to start, stop—just the expectations of my job—come into play too when wearing work boots. I’m on uneven ground all day, in and out of a car, you know, going up and down stairs to people’s homes, and just the daily functions of my job is where I notice my mobility comes more into play.” Ben
“We did the [roof] tear-off in a day, and it was me and five other guys, you know, did the tear-off in a day. Fifty-five 90-pound bags of shingles. I’m up on a ladder. I’m slinging bags up. It was a whole lot better [in the XF]. I wouldn’t have been able to do that in my other leg [ESF] at all. I know I wouldn’t have been able to do it and last as long as I did, you know, all day long, in the rain.” William
Other participants described expanded mobility as improved ability to safely negotiate various obstacles or terrain they encountered in their daily lives.
“I am a kitchen manager at [a casino], and it’s a pretty big place, so I’m running all over. It’s helped a lot. I’m up and down, in and around, and I’m in the kitchen a lot. Slippery surfaces are frightening. It’s [the XF] helped because it keeps my foot planted on the floor better.” Geoff
“Like if I’m going to go walk onto the beach in the sand or walk up a sand hill, I can do those things now [in the XF]. I can walk out into the ocean. I can swim with my legs on or off. I can walk through the snow to go skiing and it doesn’t—sure, I feel a little bit, like, uneasy if it’s really icy, I want to hang on to somebody, but just walking in regular fresh snow, I don’t—I don’t feel uneasy about it at all.” Carrie
Expanded mobility, perhaps the most important and commonly reported outcome for study participants, was experienced in a unique way for each individual person and his or her lifestyle.
Participants in this focus group study described outcomes that mattered most to them when asked about their experiences wearing ESF and XF prosthetic feet. Consistent with questions posed by the researchers (Table 1), many of the outcomes described were related to the design of the prosthetic foot. However, in addition to outcomes related to design, individuals in this study also highlighted the importance of external influences such as relationships with peers and prosthetists. External influences were described as contributing to indirect outcomes, such as increased confidence and expanded mobility. Through focus group discussions, lower-limb prosthesis users in this study emphasized how the outcomes that matter most to them are interrelated and can be influenced by their prosthetic components, interactions with their peers, and relationship with their prosthetist.
Findings from the present study support evidence from previous studies that examined adaptation to amputation and early prosthetic rehabilitation. People with lower-limb amputation have previously identified confidence as an essential component of successful prosthetic rehabilitation31,32 and one that can be derived from both prosthesis characteristics31 and positive interactions with peers.32 Problematic aspects of the prosthetist-patient relationship have also previously been examined.33 However, the potentially positive effect of a strong therapeutic alliance among prosthetists and patients has not been previously explored. Therapeutic alliance has been shown to correlate with increased exercise adherence in physical therapy34 and has been suggested to improve patient outcomes.35,36 Our finding of a positive influence by the prosthetist on patient outcomes suggests a similar alliance, and may warrant further examination.
Our findings also build upon a recent study that explored outcomes of importance to both prosthesis users and service providers. Schaffalitzky and colleagues17 conducted a similar qualitative inquiry with the goal of understanding benefits of prosthetic prescription. Prosthesis users in that study identified balance and safety, independence, and not being in a wheelchair as outcomes of importance. Providers additionally identified improved quality of life and reaching potential as important outcomes for their prosthetic patients.17 These outcomes, although similar to those identified in the present study, were obtained through discussions about the general benefits of prostheses. Our focus group was intended to explore specific outcomes related to specific prosthetic devices and technologies, like the XF. Notably, our sample of lower-limb prosthesis users was both younger and more active than participants in the prior qualitative study. As such, participants in our study described outcomes beyond basic mobility when asked to differentiate between ESF and XF. This was expected, as both prosthetic feet are designed for unlimited community ambulators (i.e., Medicare Functional Classification Level 3 and 4).
Outcomes identified by lower-limb prosthesis users can assist in the selection of measures that better reflect outcomes that matter, as well as those which may be able to measure changes that occur when users transition from one type of prosthetic foot to another. Some outcomes identified by our participants (i.e., balance and stability, endurance and sustained gait quality, and expanded mobility) include constructs that are familiar to clinicians and researchers. These constructs can be measured by performance-based and/or self-report measures with evidence of reliability and validity among lower-limb prosthesis users. Other constructs (i.e., naturalness, peer and prosthetist influences, and increased confidence) are more abstract and lack standardized outcomes measures capable of assessing these attributes. Table 4 provides examples of outcome measures available to assess constructs identified by this focus group. It is important to note that not all listed measures have evidence of validity for use with people with lower-limb amputation. Further, some measures were developed to assess changes in functional impairments, and may therefore not be sensitive enough to detect differences in prosthetic feet or other prosthetic components. For example, Wurdeman et al.12 found that the 6-minute walk (6MWT) test was unable to differentiate between ESF and low-activity SACH feet for moderate-to-high-activity users. The inability to detect differences between feet was thought to be the result of compensatory gait strategies participants adopted to overcome deficits in the less advanced SACH feet.12 Therefore, use of outcome measures to assess both the quantity of an activity (e.g., distance walked, time, energy expenditure) and the quality of the individual’s experience (e.g., naturalness, perceived exertion) may provide a more comprehensive assessment and detect changes that are often undetected. Morgan et al.,13 for example, recently found that, although moderate-to-high level users exhibited no significant differences in 6MWT distance using XF relative to using ESF, standardized survey instruments detected significant differences in perceived mobility, balance confidence, fatigue, activity restrictions, and functional satisfaction.
Participants in this focus group also described outcomes related to endurance and sustained gait quality. Endurance is generally measured with a walking test, such as the 6WMT. Gait quality is similarly measured using spatiotemporal or kinematic parameters. Although these outcomes are appropriate for assessing general walking capabilities in people with lower-limb amputation, participants in this study noticed the most profound differences between XF and ESF in the quality of their gait at the end of the day (i.e., after using their prosthesis for a number of hours). This result suggests that measurement of self-reported fatigue may better capture perceived differences in endurance and sustained gait quality than direct measurement, particularly if measurements are made in the morning when a user’s fatigue is low. Researchers and clinicians may be able to capture meaningful between-foot differences in gait quality among individuals late in the day, or with procedures that intentionally fatigue a participant before measurement.
Standardized measures to assess other outcomes, including naturalness and peer influence are not currently available. Naturalness, similar to quality of life, is a multidimensional construct that may be challenging to measure. Measurement of physiological and biomechanical properties such as energy expenditure, kinematics, and spatiotemporal gait parameters are often used as proxy measures for normal or natural gait. However, participants in this study described naturalness with terms related to sensory feedback, weight distribution, and symmetry in gait. Given the multidimensional nature of naturalness, development of novel self-report measures using established methods70 may be the most practical approach to measuring such a construct. Self-report measures are often developed to assess constructs, like naturalness, that are difficult to observe.71 Peer influence, another concept raised in the present focus group study, is not currently measured in prosthetics but has been identified as an important contributor to prosthetic outcomes.72,73 Development of a self-report measure to assess how an individual’s peers and peer interactions influence prosthetic outcomes could guide efforts to improve support networks and identify individuals in need of peer support. Peer support outcome measures have been developed to assess peer interactions of students74 and may serve as a model on how to assess peer support among people with lower-limb amputation.
FUTURE RESEARCH DIRECTIONS
Future research should include conduct of similar focus groups to assess saturation of themes, as well as further explore and test the framework (Figure 1) presented in this pilot study. In addition, similar qualitative methods can be applied with people who have used other prosthetic devices or technologies (e.g., microprocessor and mechanical knees, adjustable and traditional sockets, myoelectric and body-powered arms) to examine how outcomes of importance vary. Finally, outcome measures should be developed to allow quantitative assessment of outcomes identified in this study that are not well represented by standardized instruments available to prosthetists today.
The results of this focus group study provide insight into outcomes that matter most to lower-limb prosthesis users with experience using different types of contemporary prosthetic feet. Outcomes identified in this study can inform clinicians’ conversations with patients regarding user priorities and expectations. In addition, clinicians can use these results to select measures suited to assessing outcomes important to prosthesis users. Ideally, results of this focus group (and others like it) could help to identify those constructs most likely to change as users move between different prosthetic foot designs. Participants in our study generally agreed upon outcomes of importance, but they also prioritized these outcomes to varying degrees. Variability in priorities between people suggests that outcome measure selection similarly requires individual consideration rather than universal application of outcome measures. For example, individualized measures may be useful to ensure outcome measurement best aligns with individual goals and priorities.75
The results of this study are based on a single focus group of five lower-limb prosthesis users. Participants in this study represent a select subset of people with lower-limb amputation. Specifically, our sample included active adults and unlimited community ambulators who are likely to place importance on different outcomes than those for people with lower mobility. The sample size for this study was relatively small, and saturation of themes could not be assessed with only a singular focus group. It is possible that other themes exist but were not supported by the questions asked by researchers or discussions had by participants in this study. The conduct of additional focus groups along with the use of a saturation matrix would allow researchers to assess new themes and continue recruitment of participants for focus groups until saturation of ideas is achieved. In addition, qualitative research findings are not considered generalizable, but are viewed as individual experiences that can inform understanding of a particular phenomenon. Transferability of findings in this study to others with lower-limb amputation should be made with caution.
The focus group described in the present study is an example of how user engagement through qualitative methods can be employed to identify outcomes that matter to prosthesis users. Outcomes identified through this study were described by people with experience using ESF and XF, two contemporary prosthetic foot technologies. The outcomes identified in our focus group may apply to other prosthetic feet, or even other prosthetic technology. However, further research is required to determine whether results of the current study generalize to other prosthetic components.
Current approaches to assessing and comparing effectiveness of different prosthetic foot designs have often been unable to detect outcomes perceived by prosthesis users. Qualitative methods like the pilot focus group conducted in this study can be employed to better understand specific outcomes that matter to lower-limb prosthesis users with experience using different prosthetic technologies. This study serves as an example of how qualitative methods can guide selection of outcomes most important to people with lower-limb amputation.
The authors wish to acknowledge Dagmar Amtmann, PhD, for her assistance with focus group planning.
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