Estimating upper extremity joint loads of persons with spinal cord injury walking with a lower extremity powered exoskeleton and forearm crutches.

Lower extremity powered exoskeletons with crutch support can provide upright mobility to persons with complete spinal cord injury (SCI); however, crutch use for balance and weight transfer may increase upper extremity (UE) joint loads and injury risk. This research presented the first exoskeleton-human musculoskeletal model to estimate upper extremity biomechanics, driven by 3D motion data of persons with complete SCI walking with an exoskeleton and crutch assistance. Forearm crutches instrumented with strain gauges, force plates, and a 3D motion capture system were used to collect kinematic and kinetic data from five persons with complete SCI while walking with the ARKE exoskeleton. Model output estimated participant upper extremity kinematics, kinetics, and crutch forces. Compared to inverse dynamic biomechanical crutch model studies of persons with incomplete SCI, exoskeleton users walked with more anterior trunk tilt and twice the shoulder flexion angle. Anterior tilt increased forces and moments at the crutch, shoulder, and elbow. Crutch floor contact periods were 30-40% longer, resulting in upper extremity joint impulses 5 to 12 times greater than previously reported. Reducing UE joint loading is important to reduce overuse injuries associated with ambulatory assistive devices. Incorporating a variable assist ankle joint or more experience with exoskeleton walking may reduce UE joint loads, and minimise injury risk. Study outcomes provide a quantitative understanding of UE dynamics during exoskeleton walking that can be used to improve device design, training, and rehabilitation.

Modeling and Simulation of a Lower Extremity Powered Exoskeleton.

Lower extremity powered exoskeletons (LEPEs) allow people with spinal cord injury (SCI) to stand and walk. However, the majority of LEPEs walk slowly and users can become fatigued from overuse of forearm crutches, suggesting LEPE design can be enhanced. Virtual prototyping is a cost-effective way of improving design; therefore, this research developed and validated two models that simulate walking with the Bionik Laboratories' ARKE exoskeleton attached to a human musculoskeletal model. The first model was driven by kinematic data from 30 able-bodied participants walking at realistic slow walking speeds (0.2-0.8 m/s) and accurately predicted ground reaction forces (GRF) for all speeds. The second model added upper limb crutches and was driven by 3-D-marker data from five SCI participants walking with ARKE. Vertical GRF had the strongest correlations (>0.90) and root-mean-square error (RMSE) and mediolateral center of pressure trajectory had the weakest (<0.35), for both models. Strong correlations and small RMSE between predicted and measured GRFs support the use of these models for optimizing LEPE joint mechanics and improving LEPE design.