Clinical effectiveness and safety of powered exoskeleton-assisted walking in patients with spinal cord injury: systematic review with meta-analysis

Abstract

Background: Powered exoskeletons are designed to safely facilitate ambulation in patients with spinal cord injury (SCI). We conducted the first meta-analysis of the available published research on the clinical effectiveness and safety of powered exoskeletons in SCI patients.

Methods: MEDLINE and EMBASE databases were searched for studies of powered exoskeleton-assisted walking in patients with SCI. Main outcomes were analyzed using fixed and random effects meta-analysis models.

Results: A total of 14 studies (eight ReWalk™, three Ekso™, two Indego(®), and one unspecified exoskeleton) representing 111 patients were included in the analysis. Training programs were typically conducted three times per week, 60-120 minutes per session, for 1-24 weeks. Ten studies utilized flat indoor surfaces for training and four studies incorporated complex training, including walking outdoors, navigating obstacles, climbing and descending stairs, and performing activities of daily living. Following the exoskeleton training program, 76% of patients were able to ambulate with no physical assistance. The weighted mean distance for the 6-minute walk test was 98 m. The physiologic demand of powered exoskeleton-assisted walking was 3.3 metabolic equivalents and rating of perceived exertion was 10 on the Borg 6-20 scale, comparable to self-reported exertion of an able-bodied person walking at 3 miles per hour. Improvements in spasticity and bowel movement regularity were reported in 38% and 61% of patients, respectively. No serious adverse events occurred. The incidence of fall at any time during training was 4.4%, all occurring while tethered using a first-generation exoskeleton and none resulting in injury. The incidence of bone fracture during training was 3.4%. These risks have since been mitigated with newer generation exoskeletons and refinements to patient eligibility criteria.

Conclusion: Powered exoskeletons allow patients with SCI to safely ambulate in real-world settings at a physical activity intensity conducive to prolonged use and known to yield health benefits.

Keywords: Ekso; Indego; ReWalk; SCI; ambulation; orthosis.

Figure 1

PRISMA flow diagram. Abbreviation: PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Figure 2

Ability to ambulate using a powered exoskeleton without physical assistance. Notes: Data represent the proportion of subjects who were able to ambulate using an exoskeleton without physical assistance at the end of the training period. Fixed effects estimates: 76.2% (95% CI: 66.7%–84.1%); random effects estimates: 76.2% (95% CI: 58.6%–90.1%); I²=73%, P<0.001. Abbreviation: CI, confidence interval.

Figure 3

Outcomes of randomized controlled trial comparing powered exoskeleton, reciprocating gait orthosis, and hip-knee-ankle-foot orthosis. Notes: A is PCI, B is 6-min walk distance, and C is walking velocity. *Exoskeleton outcomes superior to RGO and HKAFO for walking velocity (both P<0.001), 6-minute walk distance (P=0.03 vs RGO; P<0.01 vs HKAFO), and PCI (both P<0.001). Abbreviations: HKAFO, hip-knee-ankle-foot orthosis; PCI, physiological cost index; RGO, reciprocating gait orthosis.

Figure 4

Six-minute walk test results with a powered exoskeleton. Notes: Data represent the number of meters walked with exoskeleton at the end of the training period. Fixed effects estimates: 99 m (95% CI: 92–106 m); random effects estimates: 98 m (95% CI: 80–117 m); I²=85%, P<0.001. Abbreviation: CI, confidence interval.

Figure 5

Metabolic equivalents with powered exoskeleton walking. Notes: Data represent the number of metabolic equivalents (METs) required for exoskeleton walking at the end of the training period. METs were calculated as 1 MET per 2.7 mL O₂/kg based on the estimated or measured maximal aerobic capacity values, unless otherwise specified. Fixed effects estimates: 3.9 METs (95% CI: 3.8, 4.0 METs); random effects estimates: 3.3 METs (95% CI: 2.2, 4.4 METs); I²=98%, P<0.001. Abbreviation: CI, confidence interval.

Figure 6

Rating of perceived exertion with powered exoskeleton walking. Notes: Data represent subjective rating of perceived exertion (RPE; Borg 6–20 scale) required for exoskeleton walking at the end of the training period. Fixed and random effects estimates: 10.1 (95% CI: 9.0, 11.3); I²=0%, P=0.97. Abbreviations: CI, confidence interval; RPE, rating of perceived exertion.

Figure 7

Spasticity decreases with powered exoskeleton training. Notes: Data represent the proportion of subjects who reported decreases in spasticity with exoskeleton training. Fixed effects estimates: 36.7% (95% CI: 21.9%, 53.6%); random effects estimates: 37.7% (95% CI: 18.5%, 59.2%); I²=46%, P=0.12. Abbreviation: CI, confidence interval.

Figure 8

Improvements in bowel movement regularity with powered exoskeleton training. Notes: Data represent the proportion of subjects who reported improvements in bowel movement regularity with exoskeleton training. Fixed effects estimates: 57.7% (95% CI: 37.3%, 76.3%); random effects estimates: 60.9% (95% CI: 19.5%, 94.5%); I²=81%, P<0.01. Abbreviation: CI, confidence interval.

Figure 9

Incidence of falls with a powered exoskeleton. Notes: Data represent the proportion of subjects who experienced a fall at any point during the training period. Fixed effects estimates: 4.3% (95% CI: 1.1%, 10.8%); random effects estimates: 4.4% (95% CI: 1.0%, 10.0%); I²=11%, P=0.34. Abbreviation: CI, confidence interval.

Figure 10

Incidence of fractures with a powered exoskeleton. Notes: Data represent the proportion of subjects who experienced a bone fracture at any point during the training period. Fixed effects estimates: 3.4% (95% CI: 0.7%, 9.5%); random effects estimates: 3.4% (95% CI: 0.7%, 8.1%); I²=0%, P=0.98. Abbreviation: CI, confidence interval.