Effects of an exoskeleton-assisted walking program on bone strength in wheelchair individuals with spinal cord injury: A preliminary study using imaging and serum biomarkers

Abstract

BACKGROUND: Lower extremity weight bearing is a key determinant in maintaining bone density and strength. Approximately 60% of individuals with chronic spinal cord injury use a wheelchair long-term as their primary mode of locomotion—leading to a substantial reduction in lower extremity weight bearing. Unfortunately, this contributes to the development of severe sub-lesional osteoporosis, particularly at the femur and tibia, with fragility fracture rates twice those reported among the general population. Overground exoskeleton-assisted walking programs provide a novel opportunity to increase lower extremity weight bearing and mobility which may strengthen bone and mitigate fracture risks and associated complications. OBJECTIVES: To measure the immediate effects of an exoskeleton assisted walking program on lower-extremity bone strength and serum bone biomarkers in individuals with a spinal cord injury who use a wheelchair as their primary mode of locomotion. METHODS: Ten participants completed a 16-week exoskeleton assisted walking program incorporating 34 individualized 1-hour sessions, progressing from 1 to 3 sessions per week. Outcomes were measured immediately before and after completion of the intervention (±7 days). Mechanical bone properties (density, mineral content, geometry and strength indexes) were assessed using dual-energy X-ray absorptiometry (left hip, left arm, left leg) and peripheral quantitative tomography (25% left femur, 66% left tibia). Bone turnover biomarkers (bone formation = osteocalcin, bone resorption = telopeptide-c collagen) and 25-hydroxyvitamine D were assessed using fasting blood samples. Wilcoxon signed-ranked tests were used to determine pre versus post differences ( p<0.05) in outcomes and standardized effect sizes (ES) were computed. RESULTS: At the femur, statistically significant increases in cortical bone mineral density (ES=0.652) and stress-strain index (ES=0.889), as well as decreases in cortical bone mineral content (ES=0.889), cortical cross-sectional area (ES=0.889) and cortical thickness (ES=0.849) were observed. At the tibia, a statistically significant increase in polar moment of inertia (ES=0.790) was observed. Levels of 25-hydroxyvitamine D increased significantly (ES=0.693). CONCLUSION: The completion of a 16-week exoskeleton-assisted walking program elicits promising bone responses. However, due in part to a lack of statistical power, the clinical significance of these findings as well as the ultimate effect on bone strength and fracture risk remains to be confirmed. Larger clinical trials are needed. Longer intervention durations, as well as multimodality interventions (e.g., functional electrical stimulation, pharmacotherapy, dietary) may ultimately prove to be the most effective. This work was supported by the Fonds de recherche du Québec - Santé (FRQS, grant #252532) and the John R. Evans Leaders Fund of the Canada Foundation for Innovation (grant #36243). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.