Introduction

Orthotic gait training is usually considered for spinal cord-injured (SCI) patients during their rehabilitation process to enable them to stand and ambulate. Although the effectiveness of walking with orthoses has been shown in previous studies in this field, the high energy cost of walking with orthoses is reported as the main reason of rejection rate in these patients.1, 2, 3, 4 According to the required compensatory upper limb and trunk motion to facilitate the swing motion of the paralyzed lower limb, SCI patients inevitably require larger energy expenditure for orthotic gait.5, 6, 7 Furthermore, it can be pointed out that the various orthotics options according to joints sections considerably influence the gait function and energy expenditure in SCI patients.

In a recent literature review, Arazpour et al.8 evaluated the walking efficiency during orthotic gait of SCI paraplegics and determined that there is limited evidence, if any, in terms of superiority of powered orthoses on mechanical orthoses. In a review of mechanical and hybrid orthoses of walking in paraplegic patients, Nene et al.9 also noted that mechanical orthoses were used only for exercise purposes. These systems in general were worn for a few hours in a week because of the high rate of energy consumption used during walking with these orthoses.9 In comparison, Karimi noted differences between mechanical orthoses and hybrid orthoses in various kinetic parameters and energy consumption and stated that mechanical orthoses were more effective in providing stability and reducing energy consumption during walking in paraplegic patients.10 In another review, Arazpour et al. reported on the walking efficiency of powered orthoses on walking in paraplegic subjects.11 Although the effect of orthosis options in walking in paraplegic subjects is well reported, it is not clear to what extent the orthosis options for various joints sections influence gait function performance. The aim of the present review was to analyze the different orthosis with and without reciprocation mechanism or another type of exertion mechanism (for example, orthoses that modified hip joints, knee joints and ankle joints) and powered exoskeleton on the improvement of walking in the SCI patients.

Methods

Search strategy

A search was performed using the Population Intervention Comparison Outcome (PICO) method, based on selected keywords and their composition (Table 1). By using ‘OR’, ‘AND’, ‘NOT’ words between the considered keywords, studies were identified electronically in the Science Direct, Google Scholar, Scopus, Web of Knowledge and PubMed databases. Studies were selected by hand searching the reference lists of the electronically identified studies. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method was used to report the results. Assessment of the quality of all articles was performed based on the Physiotherapy Evidence Database (PEDro scale). Studies that follow to the outcome measures were included in the final review. According to the chosen inclusion and exclusion criteria, 29 articles were subsequently chosen for final evaluation.

Table 1 Selected key words using the PICO method
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Inclusion and exclusion criteria

Table 2 demonstrates the inclusion and exclusion criteria in this study. The studies that were considered for inclusion were randomized clinical trials (RCTs), case–control trials, cohort studies, case series studies and single-case studies. Language or year of publication was not considered as restrictions. Studies reporting the effect of all types of mechanical orthoses such as Hip Knee Ankle Foot Orthosis (HKAFOs), Knee Ankle Foot Orthosis (KAFOs), the Louisiana State University Reciprocating Gait Orthosis (LSU RGO), the Advanced Reciprocating Gait Orthosis (ARGO), the Isocentric Reciprocating Gait Orthosis (IRGO), the Parawalker, the Hip Guidance Orthosis (HGO), the Primewalk orthosis, the Walkabout orthosis (WO), the Moorong medial linkage orthosis and powered orthosis (for example, Rewalk, wearable power assist locomotor orthosis (WPAL), the hybrid-assisted limb orthosis (HAL)) designs on paraplegic ambulation were selected for further analysis. Papers were selected from peer reviewed journals, which demonstrated or reported energy consumption, temporal spatial, kinematics and kinetic effects of mechanical orthoses with adding options or alternation in components used in SCI subjects. Studies that included alternative outcome measures, employed ‘body weight support systems with robot-assisted gait', compared primary outcome measures between patients with different disabilities and those that tested orthoses with healthy volunteer subjects (even though the orthoses of interest were utilized in the study) were also excluded. The abstracts and full text of all of the studies found in all databases were compared with the inclusion criteria by two independent reviewers.

Table 2 Inclusion and exclusion criteria utilized to select articles
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Results

The studies identified for those with SCI are either individual case reports or individual subject data from a multiple case series and are therefore classified as poor quality papers (Tables 3, 4, 5, 6). PEDro scores ranged from 1 to 4 across studies, with a median value of 2.

Table 3 The studies that evaluated the effect of modified hip joints on gait parameters in the SCI patients
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Table 4 The studies that evaluated the effect of modified knee joints on gait parameters in the SCI patients
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Table 5 The studies that evaluated the effect of modified ankle joints and foot sections on gait parameters in the SCI patients
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Table 6 Studies investigating the effects of powered orthosis and exoskeleton on gait parameters by SCI subjects
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Studies that evaluated modified hip joints on gait parameters in the SCI patients

Table 3 demonstrated studies that evaluated the modified hip joints on gait parameters in the SCI patients. Twelve studies evaluated the effects of different hip joint options on walking parameters and energy expenditure.5, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 These studies had low level of evidence according to the PEDro score (2/10). Table 3 provides details on the studies evaluating modified hip joints in patients with SCI. As outlined in Table 3, in 4 of 12 studies, functional electrical simulation (FES) with and without RGO was evaluated in comparison with a mechanical orthosis (for example, long leg brace and medial linkage orthosis).5, 12, 17, 19 In 7 of 12 studies, different mechanical orthoses compared with each other, and it has proved that various forms of RGOs have a higher velocity and lower energy expenditure in comparison with conventional and medial linkage orthoses.13, 14, 15, 16, 18, 21, 22 Only one study compared a powered orthosis with two other mechanical orthoses.23

There were three types of mechanical hip joint mechanism (HKAFO, RGO and medial linkage orthosis (MLO)) in orthoses, which were used in walking in SCI patients. A simple hip joint with one degree of freedom generally was used in the HKAFO as the first mechanism of hip joint system. Paraplegic patients use a swing through walking pattern during ambulation with this type of orthosis. RGO, as the second mechanism of hip joint system, were introduced in the late 1960s. The hip joints linked together to provide reciprocal motions of both hip joints that connected two sides KAFOs. Within this type of orthosis, a hip mechanism prevents uncontrolled collapse of the trunk and allows freely upper extremities movement of SCI patients. A modified version of RGOs is referred to as the advanced reciprocating gait orthosis (ARGO) with a one pull–push cable within the pelvic section developed to assist walking performance in paraplegic subjects. A more developed RGO is defined as the isocentric reciprocating gait orthosis (IRGO) and was introduced by Motlock in 1992.24 Another type of mechanical orthosis is MLO as the third mechanism of the hip joint system. There are variations of this type of orthosis, which include the Walkabout,25 Moorong16 and Primewalk,26 the HALO18 and new reciprocating MLO.27

Studies that evaluated modified knee joints on gait parameters in SCI patients

Table 4 demonstrated studies that evaluated the modified knee joints on gait parameters in the SCI patients. Five studies investigated the role of knee joint options on gait parameters and compensatory trunk motion.28, 29, 30, 31, 32 These studies had a low level of evidence according to the PEDro score (2/10). In an identifying paper, it has been shown that adding FES to knee extensor (quadriceps) muscles with the RGO system reduces heart rate and energy expend.

All of the RGOs that are used for ambulation in paraplegic patients hold the knee in a locked and extended position. Combination of these orthoses with external actuators or using mechanical stance control orthosis in this type of orthosis can refine and provide a suitable means of progression of rehabilitation and technology this field. Developments in the mechanical design,29 hybrid orthoses33, 34 active powered knee joints,20, 32 the pneumatic artificial limb in KAFO,35 motorized SCKAFO36 and motorized KAFO37 have been introduced to provide knee flexion during the swing phase of walking by SCI patients.

Studies that evaluated modified ankle joints on gait parameters in SCI patients

Table 5 demonstrated studies that evaluated the modified ankle joints on gait parameters in the SCI patients. Only five studies analyzed modified ankle joints on gait parameters in SCI patients.33, 34, 38, 39, 40 These studies had a low level of evidence according to the PEDro score (2/10). All five studies measured gait parameters and balance with changes in ankle joint from solid to dorsiflexion assist and also adding some changes in shoe such as rocker. In only two studies, energy expenditure was measured.39, 40

Studies investigating the effects of powered orthosis and exoskeleton on gait parameters in SCI subjects

Table 6 shows studies investigating the effects of powered orthosis and exoskeleton on gait parameters by SCI subjects. Nine studies analyzed gait parameters in SCI patients as powered orthoses and exoskeleton.41, 42, 43, 44, 45, 46, 47, 48, 49 These studies had a low level of evidence according to the PEDro score (2/10). Powered lower limb orthoses such as the HAL-5 Type-C (hybrid assistive limb), which has five electric motors45,50 the ReWalk powered orthosis (Argo Medical Technologies),42, 43 the wearable power assist locomotor (WPAL)41 and the e LEGS powered orthosis (Berkeley Bionics) are all examples of commercially developed powered orthoses designed for walking by individuals with paraplegia.

Discussion

Walking with a mechanical orthosis is not ideal for SCI patients because of high loads on upper limb joints and high rate of energy consumption. Some authors have also stated that walking with mechanical orthoses is boring and exhausting.13, 28 Improvement of the mechanical structure of the orthosis and using external power to drive the mechanical orthoses are reported as the two methods that show improvement of gait parameters in paraplegic patients.8 The mechanical orthoses have a simple structure and user friendly design. This type of orthosis, however, has not progressed in development in recent years, as technology of the powered orthoses appears to be the main focus of research in rehabilitation and assisted walking and ambulation in SCI patients.

The influence of the modified hip joint systems on walking in SCI patients

The prescribed option in improvement of walking parameters between mechanical orthoses is the IRGO system. Evaluation of the hip joint mechanism when using the IRGO has been reported to demonstrate improved gait parameters and energy consumption compared with other RGOs, HKAFO and MLOs.51 The difference between walking with optimal mechanical orthoses (IRGOs) with healthy subjects walking is high.23, 52 Recent efforts to improve orthoses for SCI patients have led to systems of orthoses that combine the mechanical orthoses with functional electrical stimulation of selected lower extremity muscles and powered orthoses.5, 10, 19, 53 There are currently only a limited range of powered orthoses, but there is some evidence of an increase in temporal spatial parameters when walking with powered orthoses.54, 55 The results of the reviewed studies suggest positive effects of external power (for example, Rewalk, HAL and WPAL) or improvement of the mechanical structure of the orthosis on gait parameters in paraplegic patients.56 Generally, walking parameters and energy consumption improved with new generation of orthoses.53, 57 The evidence to date suggests that powered orthoses have the capability to improve specific gait parameters when compared with non-powered mechanical orthoses such as the IRGO,11, 54, 58, 59, 60 a conventional HKAFO60 and the ARGO.30, 61

Walking with the IRGO was considered as the higher levels of walking parameters between the RGOs in the SCI patients. The means of speed of walking were reported 0.17, 0.19, 0.22, 0.25 and 0.34 m per second.14, 15, 20, 62, 63 The mean of energy consumption was reported 120±6 to 140±11 beats per min) 144 beats per min.14, 62 In the modified hip joint category in using MLO, the values of this parameter were reported 0.11, 0.14, 0.33 m per second with WO,16, 26 0.13 with Moorong, 0.6 m per second with HALO16, 18 and 0.39 with new reciprocating MLO.21 In using powered hip joint, the mean of walking speed was announced 0.40 m per second compared with 0.16 m per second in using orthosis without hip actuator.30 It shows that adding FES to mechanical orthosis reduced heart rate and improved walking speed during ambulation,19, 28 but using MLO increased the PCI (as the energy consumption predicator) compared with IRGO (155 beats per min, 164 beats per min).16 In wearing new reciprocating MLO, the PCI was reduced in four SCI patients.22

The influence of the modified knee joint on walking in SCI patients

Walking with orthoses that locked the knee in extension demonstrated less gait efficiency compared with the orthoses with provided knee flexion. In addition, an increase in temporal spatial parameters (speed of walking, cadence, step length) was reported with powered knee joints or unlock able knee joint compared with a mechanical orthosis (for example, IRGO, ARGO) in SCI patients.30, 31, 32 In the modified knee joint category in using mechanical linked knee ankle joints, the value of the speed of walking reported 0.14 m per second.29 Using powered knee joint associated with ARGO, IRGO had significant influence. The rate of walking speed reported 0.53, 0.31 and 0.33 m per second.30, 31, 32 Energy consumption was not evaluated when modified knee joint was used in the SCI patients. On the basis of knee extension position in the mechanical orthoses, reduction in compensatory motion is demonstrated by using powered orthosis55 or IRGO with stance control knee joint in SCI patients.64 The reduction in energy consumption is shown related to the reduction in vertical and horizontal compensatory motions in SCI patients.

Gas-powered knee joint is similar to the knee joint used in ARGO, provides stability in stance during walking and aids in standing from a sitting position with orthoses. The results of walking with a stance control knee joint were demonstrated with IRGO in one SCI patient,64 and it was noted that there was poor control of knee joint. It therefore appears that this type of knee joint is not a good option in SCI patients.

Knee flexion during walking is one determinant that was used to smoothing the center of the mass pathway and reduced energy consumption during walking. This parameter is very important especially in patients with double lower limb weakness (for example, paraplegic patients).53, 65 Knee flexion in walking provided less compensatory motion during ambulation66 and during orthotic gait these parameters are thought to increase. It is noted that knee flexion during orthotic gait produced more ground clearance and fewer compensatory motions compared with a fixed extended knee during walking.29 In comparison, it was reported that the lack of knee flexion during the swing phase of gait could be the main reason of rejection and fatigue in paraplegic patients.67, 68

The influence of modified ankle joint and foot sections on walking in SCI patients

The ankle joint has a critical role in facilitating forward propulsion during walking by moving the center of mass forward during push-off, with the ankle plantar flexor muscles performing a pivotal role during this phase. This action can cause a reduction in energy expenditure.69, 70, 71 In other words, to control walking and the alternation, the motor output of spinal motor neurons reciprocating limb loading,72, 73, 74 the afferent feedback from the ankle joint is important.

When using an AFO with dorsiflexion assist in ARGO and using a hip and ankle linked orthosis (HALO) mechanism, the cadence and the speed of walking (ARGO:0.35 m per second, HALO:0.60 m per second) have been shown to improve compared with the ARGO with solid AFO and Primewalk orthosis, respectively.18 The speed of walking reported significantly faster (0.31 m per second) and energy costs reduced in paraplegic patients when the weight-bearing control orthosis (WBCO) was used compared with a previous study in this field.39 The WBCO has a reciprocal gait pattern and a movable foot portion. In all types of mechanical orthosis, the dorsiflexion assist ankle joint should be considered. This type of joint allows dorsiflexion motion in ankle in providing ‘C’ posture and in addition causes foot clearance in the swing phase of gait.

Adding rocker soles associated with the RGO is another option in improvement of walking parameter in paraplegic patients.34,40 A rocker sole provides forward progression of the tibia when sagittal plane ankle motion is restricted. In essence, it facilitates shank advancement over a stationary foot.75 The increase in walking speed (ARGO: 0.36 m per second Primewalk: 0.27 m per second) and step length, and improved sagittal plane hip joint kinematics were reported when rocker sole mechanism was used associated with the ARGO and Prime walk.34, 40 Therefore, using this type of shoe modification has the potential to improve gait parameters in SCI patients.

Quality assessment of related studies

However, from 31 studies, just eight studies have the PEDro scale of 3 and 4 in this review. From 31 studies, just four studies included between-group comparisons.12, 13, 17, 19 Fourteen studies published did not provide data with adequate internal validity, as demonstrated by low scores on the PEDro scale (2/10).The study's flaws included lack of randomization procedures, lack of control group, no masking of examiners and patients and also there was a lack of similarity among groups. These more recent studies have not substantially improved the quality of the research. Some of the proposed interpretations are often based on small sample studies with very heterogeneous participant pools. There is a continuing need for high-quality experimental studies in this area. Future studies should consider stronger designs that can control for confusing factors, such as a case report and single-subject designs. A high-quality RCT provides the best design to control for potential bias, thus offering the strongest evidence of cause-effect inferences between interventions and outcomes.

Subject's individual perception of the exertion associated with walking using an orthoses can be related to the energy consumption (good or bad), as well as having a significant impact on whether they might select to use this orthosis on a regular basis. Spadone et al.76 analyzed the perceived exertion associated with the energy consumption when using the Parastep orthosis during walking by paraplegic subjects.76 Ferguson et al.,77 Marsolais et al.78 and Hardin et al.79 demonstrated that perceived exertion in using the bracing system with FES was ‘easier’ than without stimulation. This point was not evaluated in only mechanical orthoses or powered gait orthoses.

Conclusion

On the basis of the difficulties and limitations of orthotic walking, SCI patients who wish to ambulate should be issued with the most appropriate orthotic system. According to the usage of various orthotic options proposed for walking in paraplegic patients, joint types of the orthosis appear to be critical in the improvement of walking with the orthoses. 'user friendly' orthoses with the appreciative structure (for example, hip joint with reciprocating mechanism, activated knee joint and movable ankle joint with dorsiflexion assist) allow SCI patients to walk in the most optimal of conditions when wearing the system.

These types of orthosis, even the hybrid one with reciprocating and FES, are not enough to provide a functional, efficient gait for the paraplegic patient. Another important issue is the deficit of sensory feedback and proprioception and the high demand to control the whole system with the vision and trunk/upper member’s movement.