Use of Overground Supported-Stepping Devices for Non-Ambulant Children, Adolescents, and Adults with Cerebral Palsy: A Scoping Review

: Individuals with cerebral palsy functioning at Gross Motor Function Classiﬁcation System (GMFCS) levels IV and V are unable to use hand-held walkers and require supported-stepping devices with trunk and pelvic support to allow overground stepping in natural environments. This scoping review explored what is known about the use of supported-stepping devices with individuals functioning at GMFCS IV or V. Comprehensive database and hand searches were completed in December 2022. Of 225 unique citations, 68 met the inclusion criteria: 10 syntheses and 58 primary studies including randomized, non-randomized, qualitative, observational and case study designs. Primary studies included 705 unique individuals functioning at GMFCS IV or V, aged 9 months to 47.7 years, while surveys and qualitative studies included 632 therapists. No new experimental studies have been published since previous reviews, however, lived experience and descriptive data suggest that upright positioning and mobility in supported-stepping devices have psycho-social signiﬁcance with positive impacts on individual self-esteem and autonomy, as well as inﬂuencing the perception of others. Improved head and trunk control, use of hands, stepping and independent mobility may promote ﬁtness, functioning, fun, friends, family and future, although environmental and physical challenges may limit use in adolescence and adulthood. Further research on all aspects of supported-stepping device use with individuals at GMFCS IV/V is warranted.


Introduction
Cerebral palsy (CP) is the most common cause of life-long disability and is diagnosed based on clinical symptoms. All individuals presenting with non-degenerative disorders of posture and movement due to disturbances in the fetal or infant brain fall under the umbrella definition of CP [1], with genetic and other diagnoses included [2]. The Gross Motor Function Classification System (GMFCS) classifies those with CP according to their mobility function and need for assistive devices in different age groups. School-aged children functioning at level I walk without aids as their primary method of community mobility, while those functioning at level V have very limited abilities to maintain or change position independently. They may achieve independent mobility in some environments using power mobility with complex adaptations [3,4].
Children, adolescents, and adults functioning at GMFCS IV and V are considered nonambulant as they are primarily dependent on wheeled mobility (with or without physical or powered assistance) [4]. They are more likely to experience secondary musculoskeletal impairments, pain, and functional limitations [5], and young adults functioning at GMFCS IV and V spend most of their day in lying and sitting positions [6].
Asymmetrical lying and inability to change position is associated with windswept hips and scoliosis [7,8]. The need to reduce sedentary behavior in individuals with CP is increasingly recommended, but engaging in physical activity is challenging for those who are non-ambulant [9]. Individuals functioning at GMFCS V may receive the fewest evidence-based interventions [10]. In this paper, the phrase 'individuals/those/children at GMFCS IV/V' refers to individuals with CP functioning or classified at GMFCS IV/V. The Prechtl General Movement Assessment Motor Optimality Score and the Hammersmith Infant Neurological Exam can be used to identify children at greatest risk of being classified at GMFCS IV or V within the first 12 months of life [11,12]. Early identification can help target management and intervention strategies appropriately. Early upright positioning and mobility experiences increase children's activity and participation, and promote overall cognitive and social development [13]. Increasing opportunities for position change and movement throughout the day may facilitate adaptive behavior and help prevent secondary impairments such as contractures, thus enhancing motor function for children with non-ambulant CP [5].
Supported-stepping devices (referred to hereafter as SSDs or stepping devices) may be used by those with non-ambulant CP to promote active movement and mobility. They are most commonly used by children, but some non-ambulant adults have been reported to use gait aids [14]. Stepping devices provide trunk and pelvic support in an upright position and are individually prescribed for use in typical home and community settings for 'walking' or stepping. They are transportable (at least in a mini-van) and this distinguishes them from institutional-type devices that are designed for use in a therapy setting by multiple individuals. Stepping devices are also known as gait trainers or support walkers and are affordances for active, overground supported stepping. The term supportedstepping device is now preferred over gait trainer, since they are not used to 'train gait' for individuals at GMFCS IV/V. Those with non-ambulant CP are not expected to progress to independent walking without the device. The term 'support walker' also implies that individuals use the device for walking, while active upright positioning and stepping may be a more accurate description for many users.
The first systematic review of supported-stepping device outcomes [15] included children up to 18 years of age with any type of disability. Outcomes were divided by International Classification of Functioning, Disability and Health (ICF) categories of body structure and function (BSF), activity, and participation [16]. Several positive findings were reported, including statistically significant impact on mobility level and bowel function and an association between increased intervention time and bone mineral density. Descriptive evidence supported a positive impact on activity (primarily stepping) and participation with others [15]. Most participants were classified as GMFCS III or IV, while only two studies specifically identified some participants as GMFCS V [17,18]. Children at GMFCS III typically use stepping devices at younger ages and progress to using hand-held posterior walkers by school age [19].
The purpose of this scoping review is to describe the outcomes and use of supportedstepping devices for individuals with non-ambulant CP. A scoping methodology was chosen [20][21][22], and the search expanded to include all ages, grey literature, supporting evidence, reviews and expert opinion as well as any qualitative or quantitative studies.
The overall question is: What is known about the use of supported-stepping devices with children, adolescents or adults with CP and classified at GMFCS IV or V?
Sub-questions articulate the scope of the enquiry as follows: • What BSF, activity, and participation outcomes from supported-stepping device use have been reported?; • Are there any data available regarding: rates of use; costs; abandonment; adverse effects; contraindications; or equipment type in relation to age, desired outcomes or GMFCS levels?; • Do experiences of stakeholders differ in regard to supported-stepping device use?; • What are the barriers and facilitators of supported-stepping device use?
A supported-stepping device is defined as a wheeled 'walking' frame or support walker that provides trunk and pelvic support and has a soft strap or solid seat. Stepping devices may provide upper limb support through a tray or arm troughs, or may be handsfree. They may support the individual from behind (posterior) or in front (anterior). Some posterior wheeled walkers that are typically considered hand-held walkers are convertible to a stepping device with the addition of trunk and pelvic supports, a sling seat, and they may also have arm troughs [19].
All study types providing data or recommendations for stepping device use with individuals at GMFCS IV/V were included: reviews, guidelines or opinion; intervention studies from randomized controlled trials to case studies; qualitative or survey studies including parents of individuals at GMFCS IV/V and/or educational staff, medical personnel or physical/occupational therapists having experience using stepping devices; and data describing use, tolerance, benefits or harms of stepping device use with individuals at GMFCS IV and/or V.

•
Studies including mainly individuals classified as GMFCS I-III or those able to walk independently or use hand-held walkers; • Studies using robotic devices, exoskeletons or mechanical stepping devices with external power sources, stationary systems (confined to parallel bars or treadmill), ceiling suspension systems or institutional-type gait trainers (e.g., LiteGait) too large to be used in a home or classroom environment; • Where overground gait or ambulatory training was the comparison intervention, studies were included only if a supported-stepping device was the main comparison and not used in combination with partial body-weight supported treadmill training or other powered intervention(s).

Data Extraction and Appraisal
Included studies were appraised independently by both reviewers, and extracted data (participants, intervention, and results/findings), study design, themes and findings agreed upon through discussion. Where details were unclear, study authors were contacted for clarification. Study design was defined using Mixed Methods Appraisal Tool (MMAT) [26] criteria. Study quality was appraised for randomized and non-randomized group studies to allow comparison of study conduct. Since lived experience was a focus of this review, quality rating was also completed for qualitative and mixed-method studies. Remaining studies were descriptive and reported in a wide variety of formats, making comparative quality rating inappropriate.
Numbers of unique individual participants classified at GMFCS IV, GMFCS V, and GMFCS IV/V were totaled, without weighing for differences in study type, publication type or study quality. For longitudinal studies where the same population was measured more than once, only numbers from the original or largest n report were included in these calculations. Only those using a stepping device were counted in comparative group studies or in studies where only some individuals used a stepping device. Outcomes of stepping device use were grouped according to the ICF categories of BSF, activity, and participation. The number of therapists reporting agreement in surveys plus the number of expert opinion authors agreeing were totaled for each outcome. The number of unique non-ambulant participants reported for each outcome was totaled, with outcomes reported from a large clinical/commercial dataset counted separately so as not to skew findings.
The F-words [27] have expanded our understanding of the ICF and how these concepts apply to childhood development. Findings from lived experience and descriptive data were classified according to the F-words to allow for a deeper analysis of environmental factors from the family perspective and a consideration of Future which is not specifically included in the ICF. Fitness relates to the ICF component of BSF. Functioning is closely aligned to the ICF component of activity and Friends is related to the ICF component of participation. Fun is related to the ICF concept of personal factors and also participation, while Family represents the major environmental factor influencing the development of children [27].
In this analysis, inclusion in school or preschool activities, being eye-to-eye with peers, a sense of belonging, and social interaction, were considered to relate to Friends. Parent satisfaction with devices and services, the impact of interventions on family and other environmental factors such as the supports and attitudes of caregivers, schools, and therapists were included under Family. Future included interventions designed to impact future functioning, health, and well-being [28].

Results
Database searches yielded 698 citations and a further 48 citations were identified through hand searching. Once duplicates were removed, 225 citations remained. Following title and abstract review, 89 full-text articles were retrieved. Following a full-text review, 68 articles met the inclusion criteria and 21 records were removed for the following reasons: not retrieved [29][30][31]; not GMFCS IV/V [32][33][34][35][36][37][38]; not a stepping device or not a stepping device only [39][40][41][42][43][44][45][46][47]; no data [48]; and duplicate data to included study [49]. See Figure 1. data were classified according to the F-words to allow for a deeper analysis of environmental factors from the family perspective and a consideration of Future which is not specifically included in the ICF. Fitness relates to the ICF component of BSF. Functioning is closely aligned to the ICF component of activity and Friends is related to the ICF component of participation. Fun is related to the ICF concept of personal factors and also participation, while Family represents the major environmental factor influencing the development of children [27].
In this analysis, inclusion in school or preschool activities, being eye-to-eye with peers, a sense of belonging, and social interaction, were considered to relate to Friends. Parent satisfaction with devices and services, the impact of interventions on family and other environmental factors such as the supports and attitudes of caregivers, schools, and therapists were included under Family. Future included interventions designed to impact future functioning, health, and well-being [28].

Syntheses and Guidelines
Syntheses of evidence related to stepping device use included two clinical guidelines [55,56], an overview of intervention efficacy [53], a systematic review and metaanalysis of functional gait training interventions [52] and a scoping review of early interventions [57]. Other than a review completed as part of an undergraduate degree in Germany [51], remaining reviews were previously completed by both authors [15,19,25,54]. See Table 1 for details. Syntheses are listed chronologically, identified by first author and reference number. Overground more effective than partial body-weight supported treadmill training to increase walking distance for GMFCS IV/V. SSDs used for inclusion and well-being rather than functional mobility.
COI: conflict of interest.

171
Apart from the thesis, syntheses authors declared any conflict of interest, and studies were either unfunded or funded by independent grants with no input on study design, conduct or reporting. No synthesis reported funding for their included studies. Where conflict of interest or funding were reported for primary studies, these are noted in Table 2. In one study [60], the device distributor had input into study design and conduct. Three descriptive articles [77,86,110] were written and provided by the device distributor.

Sources of Evidence According to Supported-Stepping Device (SSD) Type
Studies related to the David Hart or NF-walker ® (hereafter referred to as a hands-free orthotic stepping device) were the most numerous of any specifically identified stepping device, and may speak to grant funding availability. The non-randomized two-group design [17], pre-post [18,61], and qualitative [64] studies were cited in the previous systematic review [15]. Additional studies included: a pre-post study [60] from Switzerland; a conference paper [77]; a dataset describing hands-free orthotic stepping device use in Spain between 2010 and 2022 [86]; a longitudinal study by independent researchers with a small sub-set of children from this dataset [81,82]; a mixed-methods study from Finland [66]; a protocol for selection of device candidates [76]; and three case reports [103,105,106].
Mobility Opportunities Via Education (MOVE ® ) traditionally involves the use of an anterior or front-leaning stepping device with arm support for non-ambulant children. In addition to the non-randomized two-group study [59], multiple baseline design [67], and the single case report [101] cited in the previous systematic review, two observational group studies [79,83] described in conference abstracts and three case reports [97,104,107] were added.
Remaining studies included use of various stepping device types. Two recent qualitative studies explored stakeholder experiences [63,65] while two surveys explored therapist impressions, one from the UK [87] and one from the US [88]. Stepping device use data was provided by two other surveys [14,89]. A new pre-post pilot study examined the effect of short-term intensive power training during physical education on walking speed, distance, and heart rate [62]. Previously reviewed case series [75] and single case reports [93,101] were supplemented by case reports identified from reference [92,94,98,99] and periodical searches [90,100]. Expert opinion on use of stepping devices was found in two other periodicals [109,111]. Five book chapters [91,95,102,108,112] contained either case studies or recommendations specific to stepping device use with GMFCS IV/V.

Use and Introduction of Supported-Stepping Devices (SSD) According to Age and GMFCS
Studies reported or examined the use of stepping devices with 235 individuals classified at GMFCS IV, 288 at GMFCS V, and 182 identified as either IV or V. A significant proportion (105 at GMFCS IV and 180 at GMFCS V) are from the Spanish dataset [86] that includes participants from other citations [77,81,82]. In addition, 632 therapists with experience using stepping devices with those classified at GMFCS IV and V participated in survey and qualitative studies. The most common stepping device use pattern reported was 30-60 min, 5-7 days a week, with a range from 10 min to 4 h daily. Survey and longitudinal studies suggest that the average duration of use may be 5-7 years, but it ranges from 6 months to >10 years.
Excluding the unpublished dataset [86], individuals classified as GMFCS IV ranged from 9 months to 22 years, while those at GMFCS V ranged from 9 months to 17 years with an average age around 7 years. Those classified only as IV/V ranged in age from 3 years to 47.7 years. When the adult ages were removed (four aged 19.2, 34, 42.2 and 47.2 years), the average age was around 9 years. The 122 current users in Spain are 2 years to 34 years old, with an average age of 13 years. Of 47 adults, 9 began using their hands-free orthotic stepping device over 18 years of age, while 36/285 continued use into adulthood [86].
Therapist recommendations for age of introduction range from 9 months to 2 years. Two recent studies from the UK [63,87] highlight a divide between therapists who support early stepping device use to promote stepping and participation, and those who wait until it is clear that the child will not be able to walk any other way, fearing that stepping device use will increase independence at the cost of typical movement patterns. No clear trends were identified regarding stepping device type or orientation in relation to age or GMFCS level. No differences in use or introduction were identified in relation to specific outcomes.

Contraindications and Benefits of Supported-Stepping Device (SSD) Use
Studies were primarily observational or descriptive, and few harms were reported. Contraindications included pain, lack of head control (that cannot be addressed with head or neck support), flexor withdrawal response to weight on the feet, behavioral issues, lack of caregiver support and significant lower limb contractures (orthotic stepping devices only). Benefits reported include increases in physical health, physical activity, stepping ability, motivation, participation, emotional well-being and self-esteem. See Table 2 for details. Studies are organized in alphabetical order by first author within study design groups. Publication source is noted, as well as conflict of interest and funding, if reported.

Expert Opinion
Expert opinion results support the introduction of stepping devices between 1 and 2 years of age to promote upright positioning, self-esteem, physical activity, physical development and social inclusion for children at GMFCS IV/V. Decreasing sedentary behavior and promoting play, participation, and independent mobility may be more important than typical gait patterns for this population. See Table 3.

BSF, Activity and Participation Outcomes
Outcomes were divided according to ICF categories of BSF, activity and participation. Increased stepping, walking speed, distance or mobility was reported for the greatest number of individuals (303). In addition, (a) hand-use, (b) maintaining head control or standing positions (c) motivation, happiness, confidence and self-esteem and (d) participation with peers were reported for 118, 89, 67 and 76 individuals, respectively. See Figure 2a. An additional 285 individuals were reported to have improved head and trunk control, and increased self-esteem, while 245/285 were able to take steps in the stepping device with or without assistance [86].

Lived Experience of Supported-Stepping Device (SSD) Use
For studies reporting qualitative data from parents and caregivers [64][65][66]104], findings were reported according to the F-words for childhood development [27]. See Figure 3. Under the F-words analysis, there are some differences in how findings were Although improved hand function in hands-free stepping devices was reported in one synthesis [51], no experts commented on improved hand-use or transfers. Opinion was more evenly distributed between other outcomes, with impact on physical fitness most reported. See Figure 2b.

Lived Experience of Supported-Stepping Device (SSD) Use
For studies reporting qualitative data from parents and caregivers [64][65][66]104], findings were reported according to the F-words for childhood development [27]. See Figure 3. Under the F-words analysis, there are some differences in how findings were classified in comparison with the ICF analysis. Impacts on individual self-esteem and autonomy and impacts on societal or others' attitudes were included under Future, as these factors may influence future opportunities and individual potential along with influences on physical health and overall development. Happiness, enjoyment and motivation were included under Fun which combines aspects of personal factors and participation.

Discussion
In the eight years since the original systematic review [15], little has been published specifically investigating stepping device interventions. In order to explore the topic indepth, we sought out case studies, descriptive and grey literature for all ages and confirmed that successful use of stepping devices has been reported for over 700

Discussion
In the eight years since the original systematic review [15], little has been published specifically investigating stepping device interventions. In order to explore the topic in-depth, we sought out case studies, descriptive and grey literature for all ages and confirmed that successful use of stepping devices has been reported for over 700 individuals classified at GMFCS IV and V across a wide range of countries. This finding suggests that stepping device use is feasible for individuals with non-ambulant CP and may be considered standard-of-care in some settings.

Outcomes and Use of Supported-Stepping Devices (SSD)
Families, caregivers and therapists reported benefits on all components of the ICF and influencing all F-words for those classified as GMFCS V as well as GMFCS IV. Benefits were also reported for those with limited abilities to step without assistance. Introduction was demonstrated to be feasible from 9 months, in line with the call for provision of developmentally appropriate 'ON-Time' mobility [117]. Although challenges were reported in adolescence with increasing size, changed physical abilities and difficulties with transfers, this review identified at least 80 adults aged 18-47.7 years who used stepping devices. Since evidence continues to be primarily descriptive, conclusions as to efficacy of stepping device interventions are unchanged from the previous systematic review [15]. The remainder of the discussion is structured according to study aims; followed by clinical practice suggestions; and research recommendations based on the significant evidence gaps identified.

Use of Supported-Stepping Devices (SSD) for BSF, Activity, and Participation Outcomes
One included study measured a trend towards increased bone mineral density for children who spent more time weight-bearing in either a stander or a stepping device [17]. In a review of supported standing interventions for individuals at GMFCS IV/V, the strongest evidence was found for impact on bone mineral density and prevention of contractures [24]. In children with CP, differences in muscle are seen starting as early as 12-15 months when compared with children who are typically developing [118], and bone mineral density is lower in those who are non-ambulant [119]. Although no included studies examined impact on muscle length, prevention of contractures or hip stability, the benefits of stepping device use for these outcomes were reported by both therapists and parents. Early introduction of weight-bearing and promotion of upright positioning and supported stepping through adolescence into adulthood may help maintain muscle and prevent premature ageing and loss of mobility, as has been proposed for individuals with ambulant CP [120]. Parents and therapists reported benefits for bowel function following the use of stepping devices in qualitative, descriptive and survey studies, but only one study [17] measured decreased constipation for children using stepping devices in comparison to those using standers.
Physical fitness was the most highly reported benefit in the expert opinion analysis, but, until recently, no studies had examined this outcome. A small pilot study [62] measured statistically significant positive change in cardio-vascular exercise response, walking speed and distance following short-term intensive school-based physical training for children at GMFCS III and IV. Separate analysis of results for those classified as GMFCS IV only also revealed positive change, although this was greater across all measures for the younger children. The 10-11-year-old children showed minimal improvement or stable response to walking speed tests and heart rate measurement, although they were able to walk further at a self-selected walking speed on the 6-min walking endurance test. These preliminary results support use of stepping devices to increase physical fitness for children at GMFCS IV when incorporated into age-appropriate and meaningful sports activities with peers.
As in the systematic review, increased stepping, walking speed, distance or independent mobility outcomes, classified within the ICF domain of Activity, continue to be reported most frequently and were noted for 588/705 individuals in this review. However, improved head and trunk control, ability to maintain position, increased arm and hand use, improved transfers and participation in activities of daily living outcomes were also reported for large numbers of individuals across different study and report types. Although increased mobility was the primary reason for therapists prescribing a stepping device in one survey [88], physical fitness and participation outcomes may be as, or more, important.
A guideline [56], likewise, recommends that stepping devices should be used for inclusion and physical well-being rather than functional mobility for individuals at GMFCS IV/V. Case study results confirm that while children used stepping devices for participation and to reduce sedentary behavior, they relied on power wheelchairs for functional mobility and to keep up with peers over longer distances [90,91,95]. Mobility experience in stepping devices and power mobility may have reciprocal benefits. Stepping device use was not reduced, and even increased for some, following power mobility introduction in a group of young children [78]. In another study, a parent reported the benefits of increased spatial understanding from stepping device use, as it increased their child's success with power mobility [61].
In the systematic review, increased social function and improved participation were reported in only one study reporting qualitative [64] and quantitative results [61]. In contrast, increased peer participation was reported for 97 individuals across the wider range of studies in this review. In addition, therapists indicated that the use of stepping devices increased family and peer participation and enhanced child autonomy, engagement, initiation, inclusion and sense of belonging. They reported an impact on these items at a similar rate to the impact on stepping, contrasting with the focus on mobility outcomes in intervention studies.

Use of Supported-Stepping Devices (SSD) According to GMFCS Level
Little has been published regarding options to increase physical activity and decrease sedentary behavior for individuals at GMFCS V [55,56,121,122]. However, although the majority of studies in this review demonstrated that individuals at GMFCS IV can achieve independent indoor and possibly outdoor mobility in stepping devices, some at GMFCS V were also able to walk more than short distances, at least on level surfaces [60,67,76,103]. Other studies suggested that there are physical health benefits from the upright positioning and active movement opportunities. These, along with psycho-social benefits and enhancement of inclusion and participation opportunities, were reported for individuals at GMFCS V who had more limited independent stepping abilities [77,85,100,102,105].
Although no clear trends were identified in regard to GMFCS, some recommendations were made in hands-free orthotic stepping device studies. Two studies reported that individuals at GMFCS V were the typical users [81,105]. These studies include participants from the clinical/commercial dataset [86], reporting a total of 180 individuals at GMFCS V and 105 at GMFCS IV. A protocol recommends both GMFCS IV and V and suggests that cognitive and social developmental level may influence stepping [76]. Another report on a subset of 137 users from the Spanish dataset suggests that this stepping device is not beneficial for individuals at GMFCS III who may be more functional in less supportive stepping devices at younger ages and transition to posterior hand-held walkers by schoolage [77]. However, the longitudinal study from Canada [61] suggests that a number of children classified as GMFCS IV/V on study entry benefitted from the stepping device to develop trunk and upper limb control. These children (who used the stepping device daily for many hours at home, school and in community settings) progressed to using posterior hand-held walkers and were subsequently classified as GMFCS III (personal communication, Virginia Wright, 5 January 2023).

Use of Supported-Stepping Devices (SSD) in Relation to Equipment Type and Orientation
No clear trends were identified regarding stepping device type or orientation in relation to age, GMFCS or other factors. In the two surveys, anterior arm support style stepping devices were most reported. The 2011 US survey [88] suggests that the Kaye suspension system was also highly prescribed which seems unlikely. Therapists may have been reporting the prevalence of the posterior Kaye walker use rather than the addon suspension system specifically. The more recent availability of solid seat stepping devices that can be used in either reverse hands-free orientation or anterior support-arms orientation is evident in the UK survey [87]. Posterior hands-free stepping devices were prescribed at a similar rate to the anterior-posterior option in this survey in comparison to the limited use reported in the US 2011 survey. Descriptive results and clinical experience suggest that different use patterns in North America may be identified if a contemporary survey was conducted.
Although no clear trends were identified overall, some different patterns of device use were reported from different locations worldwide. Although a comprehensive longitudinal study on the hands-free orthotic stepping device took place with 20 children in Canada [18,61,64], its ongoing use in North America was very limited, likely due to the funding environment. In contrast, a number of studies were completed in Europe, with the largest dataset reported from Spain [86]. Studies including anterior support-arms stepping devices are more commonly reported in the US, likely influenced by the MOVE ® program, although MOVE ® studies were also reported in the Netherlands [59] and India [123].
More recent studies from the US report use of hands-free stepping devices with younger children at GMFCS IV and V [80,85,90,95,102], as well as different anterior styles [100]. A descriptive study found that more young children at GMFCS V used hands-free posterior stepping devices in comparison to anterior support-arm styles, while the reverse was true for GMFCS IV [78]. A recent qualitative study from Spain described the physical and psycho-social benefits of a lower-cost charity-provided hands-free walker [65], while the use of hands-free stepping devices within a US special school program was associated with a variety of developmental gains for young children at GMFCS III-V with severe visual and communication disabilities [85].
In India, commercial hands-free stepping devices are generally not available, and one study reported modifying a posterior hand-held walker with the addition of a sling seat and trunk support. This low-cost modification was acceptable to parents and provided opportunities for the children to move hands-free, increasing participation in play and activities of daily living [84]. Stepping device costs, availability and the funding environment vary widely with location influencing opportunities to use different stepping devices. No studies comparing costs or cost-effectiveness were identified in this review.

Stakeholder Experiences of Supported-Stepping Device (SSD) Use
Two surveys of pediatric therapists were completed 10 years apart; the earlier one in the US [88] and the more recent in the UK [87]. US therapists reported that 50% of children using stepping devices progress to independent walking, with 6 months the average duration of use. This suggests that stepping devices were widely used for children with developmental delays and ambulant CP who required more support in early childhood, but went on to use hand-held walkers or to walk independently.
In contrast, UK therapists reported less than 20% of children using stepping devices progressing to hand-held walkers or independent walking. While some therapists believed that early use of stepping devices could facilitate walking progression, others feared that children would learn incorrect patterns. Similarly, UK physiotherapists participating in a qualitative study [63] were divided between prioritizing child function and participation versus quality of movement. Current recommendations suggest that child and family goals for inclusion, participation, engagement and physical well-being should be prioritized over typical gait patterns for those at GMFCS IV/V [56,111,124].
In the UK qualitative study [63], parents of children at GMFCS II-IV focused on the long-term physical and social benefits of walking while children (all GMFCS II/III) prioritized having fun, playing and keeping up with friends when choosing between using their walker or wheelchair. Ambulant children may focus on Fun, Family and Friends while therapists traditionally focus on Fitness, Function and Future [124]. These perspectives have been highlighted in other studies: children see walking as exercise rather than mobility [125], adolescents prioritize safety and efficiency depending on environmental and social demands [126], and children who use mobility aids to facilitate participation in school may prefer floor mobility or assisted mobility at home [127]. These perspectives may differ for children who are unable to move even short distances without assistive devices; however, few studies report views of those at GMFCS IV/V. Since cognitive, developmental and communication difficulties are more prevalent in this group [128], parent-proxy views are more commonly reported, but may differ from the child's perspective.
Parent satisfaction was evaluated in two included studies [66,84] using the Quebec User Evaluation of Satisfaction with Assistive Technology (QUEST 2.0) [129]. Scores ranged between 4 (satisfied) and 5 (very satisfied). A study-specific satisfaction scale used in a longitudinal pre-post study [18,61] reported similar satisfaction levels.
A longitudinal study from Spain [81,82] used the children's version of QUEST 2.1 [130], which scores in the opposite direction with 1 representing the highest score and 7 the lowest. This difference in scoring, and the fact that QUEST 2.1 was designed to be more specific to satisfaction with computer technology, makes it challenging to compare parent satisfaction across studies. It is surprising that in the initial study [81], mean parent device satisfaction was 4.29 indicating mixed satisfaction, while in the 10-year follow-up study [82], a mean of 3.12 indicates parents were mostly satisfied, although only one adolescent/young adult out of 19 was still using the hands-free orthotic stepping device.
QUEST 2.0 developers suggest that ratings ≥ 4 represent acceptable satisfaction for mobility devices [131]. Studies exploring parent satisfaction with children's use of power mobility devices have reported similar ratings [132,133]. However, a survey including parents of mobility device users in Iceland [134] reported that only 57% of wheeled walker users were satisfied or very satisfied with their device features. This difference may relate to ongoing use of a range of assistive devices, in comparison to the relatively recent introduction of a novel device that may have changed the child's functioning and participation [66,84,132,133]. Continued satisfaction with a stepping device that the child could no longer use [82] may relate to the psycho-social significance of the upright position in society [64,125] and parents' memories of a time of increased participation for their children.
Parents reported least satisfaction with ease-of-use for a hands-free orthotic stepping device [66]. Difficulty with transfers into this style of stepping device is confirmed by other included studies [17,18], particularly as the child got bigger [61,64,75]. However, one descriptive case study reports a modified transfer method that allowed continued use into adulthood with one caregiver [103].

Barriers and Facilitators of Supported-Stepping Device (SSD) Use
Few harms were discussed in included studies, other than the need to ensure safety and the potential for instability or falls as children's height increases. Participants in one qualitative study commented on the stability of the stepping device used and that no falls had occurred [65]. Another study reported that two children had tipped over on uneven ground without sustaining injuries and no other harms were reported [18,61]. Transfer difficulties were the most common barriers reported overall. Other commonly reported environmental factors that could be barriers or facilitators were adequate space for use and caregiver support and supervision.
Hip, knee and ankle contractures are contraindications primarily for stepping devices with orthotic components. Increasing deformity and poor health, including contractures, hip subluxation and scoliosis, was the major reason reported for discontinuation of the hands-free orthotic stepping device [82]. In the total cohort of 285, this was also the case with the accompanying loss of ability to step, most commonly around 12-13 years of age [86]. It is not known if this would also hold true for other stepping device types. Setting up a stepping device for those with body structure or alignment differences, without increasing deformity or causing pain, may be influenced by the adjustability of the stepping device, the availability of accessories and therapist expertise. The value of the stepping device in promoting inclusion and engagement in meaningful and age-appropriate activities may also influence continued use into adolescence and adulthood.
Case series [80] and reports [96] suggest that transfers into, and stepping with anterior style stepping devices may be easier for older children. However, a variety of stepping device models have lift assistance built in and transfer aids are often used for older children. The anterior or front-leaning positioning may facilitate stepping for some children [114] and was recommended within the MOVE ® program that started with the inclusion of older children who had not been given the opportunity to move at younger ages [107]. However, angled forward positioning to facilitate stepping can also be achieved with hands-free stepping devices [135].
Outgrowing the stepping device was reported as the primary reason for discontinuation or changing to another stepping device style by parents who were motivated to continue using it with their adolescent child [64]. As the child grows taller, the device needs to be significantly wider in order to remain stable, and safety concerns at older ages have been reported [64]. Larger models suitable for adolescents and adults have been developed for some stepping devices, but they are used much less than those for younger children. The increasing width may prevent them from fitting through standard doorways, and transportation difficulties may limit use in different settings.
The recent pilot study [62] combined games activities, e.g., basketball with high intensity interval training including short bursts of speed with and without increased weight. The incorporation of the training within a supportive school setting, along with other children who had similar abilities likely contributed to the high level of adherence achieved in this study. This emphasizes the importance of inclusion and participation in meaningful and age-appropriate activities with peers as a facilitator of stepping device use in children and young people with non-ambulant CP.

Recommendations for Clinical Practice
There is still limited research that clinicians can use for clinical decision making around stepping device prescription and training. No clear trends were identified in regard to stepping device prescription and use in regard to age, GMFCS level or outcomes, and device selection may be highly influenced by availability, funding and support for use of different devices in different locations. Individualized assessment and prescription are therefore essential, and detailed case studies and single-subject research designs would add to the literature. Prescription of individual stepping devices should take into account multiple factors, including: need for postural support; positioning and support needed to allow stepping; type of transfer and equipment or support required for transfers; space for use; context and environment where the device will be used e.g., indoors or outdoors; transportation; caregiver support; and opportunities for participation and inclusion with others.
The Gross Motor Function Measure (GMFM-88) [136] has been used in research to measure the significant difference in standing or walking function, with and without the stepping device [18,61], and it may be helpful for clinicians to demonstrate the impact of a stepping device to funders or providers. The Top-Down Motor Milestone Test [137] has no composite or summary score [123], and individuals may make progress on several sub-items without changing independence level. One study modified scoring to achieve a summary score [59], but this did not account for changes in sub-items. As a result, this measure may be helpful for clinicians to record individual progress in independence within functional tasks, both with and without the stepping device, but is less suited for analyzing change in group intervention studies. Individualized goal setting measures such as the Canadian Occupational Performance Measure [138] may also be useful in clinical practice for identifying meaningful goals and measuring change for individual children. Goals varied according to GMFCS level in a recent study investigating outcomes of intensive robotic-assisted gait training. Parents of children at GMFCS III set functional mobility goals such as increasing walking speed, distance and stepping pattern, while parents of children at GMFCS IV and V set goals focused on increased independence, physical activity within the stepping device, participation in dressing and increased weightbearing during transfers [45]. This suggests that, for individuals at GMFCS IV and V, therapists should focus on outcomes that extend beyond mobility and stepping, and even beyond activities occurring while in the stepping device.

Recommendations for Future Research
Studies on all aspects of stepping device use, benefits, and development are warranted, as evidence to date is primarily descriptive and there are significant evidence gaps in every area. Accurate classification of GMFCS level is essential for future experimental studies. While GMFCS has been shown to be stable [128], there are challenges at younger ages and reclassification after age 2 years is recommended [139]. Children at GMFCS II-IV are more likely to have their level overestimated under 6 years, leading to reclassification to a lower functional level at older ages [140]. GMFCS is a continuum and children should be classified based on usual function rather than on capacity [3]; however, GMFM-66 centiles [141] may assist in classifying, particularly younger children, more accurately for research purposes. The GMFM-88 can be scored with the child using assistive devices [136] but, as yet, centiles are not available for this measure.
Using a stepping device to break up long periods spent in sitting and lying positions reduces sedentary behavior. This may impact BSF or Fitness (including hip stability), as with other postural management interventions [54], and positively influence the sleep-wake cycle [122], outcomes that have yet to be measured in experimental studies. Improvements in bowel function have only been measured in one comparative group study, and further studies are warranted. Further studies investigating exercise response to use of stepping devices with individuals at both GMFCS IV and V are also needed. The recent pilot study suggests that inclusion in sports activities with a comparable peer group may be a significant facilitator of stepping device use to increase physical activity [62] and this merits further exploration both qualitatively and quantitatively. Interventions to help prevent musculoskeletal impairments and influence societal perspectives also fall under the F-word of Future [28]. A stepping device may help to increase activity or functioning in areas such as stepping and mobility, transfers and activities of daily living, or improving head, trunk, and upper limb control. Stepping devices may also impact participation and engagement or Friends. Each of these outcomes of a stepping device intervention require different types of outcome measures.
Outcome measures suited for individuals at GMFCS IV/V to measure stepping device outcomes continue to require development [25,142]. The Canadian Occupational Performance Measure [138] has been used successfully in a robotic-assisted gait training experimental study and results suggest that wider health outcomes and health-related quality of life should be measured in future research [45]. QUEST 2.0 has also been used successfully in stepping device studies [66,84], and may be useful in comparing parent satisfaction with different stepping device types or features in relation to child and environmental factor profile.
For individuals with non-ambulant CP, no significant benefits have been found for robotic-assisted gait training in comparison to partial body-weight supported treadmill training combined with overground training [45], and overground training may be essential if the goal is to improve overground walking [58]. Studies comparing intensive overground stepping device training directly with these other technologies is warranted. Incorporating use of stepping devices in real-life activities and environments following participation in intensive training also merits investigation.
A recent scoping review on the development of individuals with CP confirmed a lack of studies exploring the impact on participation and environmental factors over time [143] and longitudinal studies of the impact of stepping devices on development are needed. Numerous studies and expert opinion comments noted the impact on emotional and psycho-social development and studies evaluating these outcomes quantitatively and over time are warranted. For individuals at GMFCS IV/V the focus for research regarding stepping device use should be less on stepping and gait pattern, and more on physical fitness, overall health and participation, engagement and quality of life outcomes.

Limitations
Although extensive hand searching was undertaken, it is challenging to search within the grey literature. Unknown researchers and unpublished studies may have been missed. Three articles were not retrieved. Results of two were described in an included study [60] and suggest improved gait pattern [30], hand function, and participation [29] for children using hands-free orthotic stepping devices. These findings are supported by other studies in this review. The remaining thesis [31] compared partial body weight-supported treadmill training and overground gait training and reported positive benefits for both, but it is unclear from the abstract whether studies included non-ambulant or ambulant CP. The comparison between partial body-weight-supported treadmill training and overground gait training has been addressed by other included syntheses [52,55,56].
This review included primarily descriptive evidence, some of which was only reported in conference abstracts. Some case reports were described in book chapters and magazine articles, and the level of detail and quality of reporting varied. A quality rating tool was therefore inappropriate for the majority of included studies, and only used to allow comparison between the group intervention and qualitative studies. Conflict of interest and influence of funding sources was mainly reported in peer-reviewed studies. Although only one article reported that the funder and device distributor had input into the planning and conduct of the study [60], it is possible that this may have been the case in other included studies, but was not noted due to differing reporting and publication standards.
In synthesizing results for visual presentation, no allowance was made for the relative quality of different studies, and a simple count of participants for each outcome was calculated. The unpublished longitudinal data from Spain [86] came from a commercial source and was collected in clinical practice rather than in the context of a research study. It included 40% of the total participants at GMFCS IV/V and therefore outcomes were reported separately to avoid skewing overall findings with data from a non-peer reviewed source, a single location, and reporting a single stepping device type. However, interestingly, that dataset did confirm three of the five major outcomes (improved head and trunk control; emotional development; stepping and mobility) drawn from all included studies.
Although higher quality evidence was not identified since the previous systematic review, this review provides a more in-depth exploration of outcomes and the lived experience for individuals functioning at GMFCS IV and V. The significant number of participants included from a wide range of ages, settings, and countries may increase the credibility and transferability of the findings.

Conclusions
Use of supported-stepping devices is feasible for children, adolescents, and adults functioning at GMFCS IV and V, with introduction as young as 9 months of age. Benefits include impact on emotional and psycho-social development, improved head, trunk, and upper limb control, communication, inclusion and participation with others. Minimal harms have been reported other than the need to ensure safety and stability as children increase in size. Contraindications include pain and flexor withdrawal response to weightbearing. Adequate family or caregiver support is essential to ensure safety, inclusion, engagement and participation in meaningful activities and routines.
Increased ability to step was reported for most users, although stepping devices are primarily prescribed to enhance physical fitness and participation for individuals functioning at GMFCS IV and V, rather than for functional mobility. Although there are challenges with the continued use of stepping devices into adulthood due to increasing physical limitations, a lack of appropriately sized devices, and transfer difficulties, feasibility for some has been demonstrated. Evidence for stepping device use continues to be primarily descriptive, but the significance of upright positioning and mobility cannot be overstated for reducing sedentary behavior and positively impacting self-esteem and participation, and positively influencing the perceptions of others for individuals with non-ambulant CP.
Author Contributions: Conceptualization, R.W.L. and G.S.P.; formal analysis, R.W.L. and G.S.P.; writing-original draft preparation, R.W.L.; writing-review and editing, G.S.P. and R.W.L. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Data Availability Statement:
The data supporting the findings of this study are mainly available within the article and its supplementary materials. Any additional data is available from the corresponding author upon reasonable request.