Lower Extremity Exoskeleton for Human Spinal Cord Injury: A Comprehensive Review

Locomotion disorder caused by spinal cord injury (SCI) leads to a considerably decreased quality of people's lives. Although there are no known cure methods for SCI, a lower extremity exoskeleton (LEE) has a perspective to restore the locomotion ability of SCI patients. Statistics show that the number of published articles on LEEs has exponentially increased over the past 20 years; however, no reviews have been conducted to summarize these studies comprehensively. To fill up this open gap, a comprehensive review from engineering to clinical standpoint is carried out, which is based on the preferred reporting items for systematic reviews and meta-analyses' methods, including their structural designs, drive forms, control methods, and clinical assessments. A systematic discussion among them is performed while considering the main scientific and technical aspects. The analysis indicates that the actuator configuration, motor selection, state transition, trajectory tracking, transparency implementation, and clinical factor design in exoskeleton development are full of challenges, which should be investigated in more technical efforts in the future.