Optimal Combination of Minimum Degrees of Freedom to be Actuated in the Lower Limbs to Facilitate Arm-Free Paraplegic Standing

Abstract

Arm-free paraplegic standing via functional electrical stimulation (FES) has drawn much attention in the biomechanical field as it might allow a paraplegic to stand and simultaneously use both arms to perform daily activities. However, current FES systems for standing require that the individual actively regulates balance using one or both arms, thus limiting the practical use of these systems. The purpose of the present study was to show that actuating only six out of 12 degrees of freedom (12-DOFs) in the lower limbs to allow paraplegics to stand freely is theoretically feasible with respect to multibody stability and physiological torque limitations of the lower limb DOF. Specifically, the goal was to determine the optimal combination of the minimum DOF that can be realistically actuated using FES while ensuring stability and able-bodied kinematics during perturbed arm-free standing. The human body was represented by a three-dimensional dynamics model with 12-DOFs in the lower limbs. Nakamura's method (Nakamura, Y., and Ghodoussi, U., 1989, "Dynamics Computation of Closed-Link Robot Mechanisms With Nonredundant and Redundant Actuators," IEEE Trans. Rob. Autom., 5(3), pp. 294-302) was applied to estimate the joint torques of the system using experimental motion data from four healthy subjects. The torques were estimated by applying our previous finding that only 6 (6-DOFs) out of 12-DOFs in the lower limbs need to be actuated to facilitate stable standing. Furthermore, it was shown that six cases of 6-DOFs exist, which facilitate stable standing. In order to characterize each of these cases in terms of the torque generation patterns and to identify a potential optimal 6-DOF combination, the joint torques during perturbations in eight different directions were estimated for all six cases of 6-DOFs. The results suggest that the actuation of both ankle flexionextension, both knee flexionextension, one hip flexionextension, and one hip abductionadduction DOF will result in the minimum torque requirements to regulate balance during perturbed standing. To facilitate unsupported FES-assisted standing, it is sufficient to actuate only 6-DOFs. An optimal combination of 6-DOFs exists, for which this system can generate able-bodied kinematics while requiring lower limb joint torques that are producible using contemporary FES technology. These findings suggest that FES-assisted arm-free standing of paraplegics is theoretically feasible, even when limited by the fact that muscles actuating specific DOFs are often denervated or difficult to access.

Bone Anchors—A Preliminary Finite Element Study of Some Factors Affecting Pullout

“…From the original volume, bone of different densities can be created by modifying the threshold values in the software [26,27]. For this study two densities of bone have been created: one by smoothing a closely approximated geometry of the original bone (lower, Fig.…”

Restoring standing capabilities with feedback control of functional neuromuscular stimulation following spinal cord injury

“…Approaches that identify optimal control structures according to current technological capabilities with specific user actions will advance the current state of the art. Implementation of hands-free FNS control systems have been shown to be plausible with elegant dynamic modeling and laboratory implementation of systems with constrained degrees-of freedom [Vette, Masani et al 59, Kim, Mills et al 60, Vette, Kim et al 61]. Although integrating the actions of the volitional upper-body with the FNS-controlled lower-body poses challenges from a control perspective, novel strategies that enable these two systems to better operate together are needed to facilitate more natural standing function.…”

“…Previous studies employing closed-loop control of FNS in simulation and laboratory experiments have demonstrated the feasibility of achieving and maintaining standing postures and minimizing upper-body support against systematic postural disturbances [Nataraj 42, Nataraj, Audu et al 43, Nataraj, Audu et al 47, Vette, Masani et al 59, Kim, Mills et al 60, Vette, Kim et al 61, Nataraj, Audu et al 74, Jaeger 75, Jaime, Matjacic et al 76, Matjacic and Bajd 77, Matjacic and Bajd 78, Tan, Masani et al 79]. However, clinical implementation of FNS for basic standing is still largely deployed in an open-loop manner.…”

Determination of the One-to-One Correspondence between the Kinematic Screw of the Output Link and the Gradient Screw in a Singular Configuration of a Parallel Mechanism

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“…it was used to reduce the number of DoFs from 12 to 6 in the lower limbs in order to theoretically achieve stable standing (with FES) in paraplegic patients without asking them using their arms [32]. This result can be extrapolated to exoskeletons in order to minimize the number of DoFs for specific positions or movements reducing at the same time the size of the exoskeleton and the power needs. …”