Background: Walking with reciprocal gait orthoses (RGO) after spinal cord injury is slow and energy inefficient, due in large part to the fixed coupling between hip flexion and extension. Increasing the ratio of hip flexion-extension coupling to 2:1 can reduce energy cost and increase step length. Further increases in walking efficiency can be obtained by allowing the knee joint to flex during swing and the ankle to plantar flex in stance. Adding functional electrical stimulation (FES) to a standard RGO increased walking distance eightfold, reduced energy expenditure by 15%-30%, and improved balance on inclines. A significant reduction in muscle fatigue was achieved with a hybrid orthosis with controlled brakes at the hips and knees when compared with FES-only gait. Combining FES with an advanced reciprocating orthosis that allows variable hip coupling should improve walking velocity and energy consumption by allowing both stride length and cadence to vary while propulsive movements are powered by the stimulated muscles.

Objectives: The primary objective of the proposed research is to design, prototype, and test a new assistive device that will restore the ability to climb stairs and walk to individuals with paraplegia. This hybrid orthosis will combine an instrumented hip knee ankle foot orthosis (THKAFO) with FES. The THKAFO will include a variable coupling hip reciprocating mechanism, locking knee and ankle joints, and variable stiffness thoracic-lumbar jacket. Actions of the brace mechanisms will be coordinated with multichannel implantable FES technology by a controller utilizing sensors to optimize joint locking and stimulus timing to reduce muscle fatigue and metabolic energy consumption.

Hypotheses: The following hypotheses will be tested as part of this research proposal. Hypothesis 1: A reciprocating hip mechanism with variable flexion-extension coupling will allow adjustable step length as the speed of walking changes while maintaining erect posture with minimal forward lean. This hypothesis will be tested in simulation and by repeated measures of kinematic and kinetic variables during walking with and without the new variable hip coupling mechanism. Outcomes to be measured include step length, cadence, walking speed, and energy consumption and efficiency. Hypothesis 2: Active ankle plantar flexion will significantly increase forward progression as measured by longer step length and faster walking as compared to a fixed ankle hybrid orthosis. This hypothesis will be tested in simulation and experimentally by monitoring gait parameters and upper body support during free locomotion with and without active ankle plantar flexion. Hypothesis 3: Incorporation of an adjustable stiffness trunk support will provide rigidity during upright posture and flexibility during sitting to significantly improve flexibility and comfort of the subject. This hypothesis will be tested by performing tasks involving transfers and retrieving objects from the floor as compared to a standard stiff brace and no brace conditions. Hypothesis 4: Combining a reciprocating hip mechanism with variable coupling and active ankle plantar flexion will provide an additive effect on gait with improvements greater than with either mechanism alone. This hypothesis will be tested by monitoring posture, step length, cadence, speed, and energy consumption and efficiency of walking as compared to implementing either mechanism alone. Hypothesis 5: Implementation of sensor-based control will increase walking distance by reducing muscle fatigue and improving the efficiency of hybrid operation. This hypothesis will be tested by repeated measures of kinematic and kinetic variables during walking with sensor-based control compared to preprogrammed hand switch control. Outcomes to be measured include step length, cadence, walking speed and distance, and energy consumption and efficiency.

Study Design: To minimize the need for prototyping and accelerate the design and testing process, we will employ a mechanical model (Working Model 3D) to simulate a person using the THKAFO with different hip reciprocator, ankle control, and thoracic designs. Two software packages, SolidWorks and COSMOS Motion (by SolidWorks Corp), will be utilized to design and test the mechanisms before they will be prototyped. Based on simulation results, the new joint mechanism will be incorporated into the brace. Joint angle and foot pressure sensors will be mounted and threshold values established to set up automatic control of joint locking and preprogrammed stimulus activation for stepping. The mechanisms will be extensively bench tested to assure that they meet the design requirements before they are applied to two able-bodied individuals to establish their safety and function. This will be followed by testing with FES in individuals with paraplegia. Quantitative gait analysis, energy consumption, and energy cost measurements will be used to test the hypotheses.

Relevance: This work is directly applicable to the health and functional independence of the paralyzed veteran. Hybrid systems combining bracing and FES have the potential to postpone or prevent medical complications associated with paralysis and improve functional independence by providing a means to exercise, stand, walk, climb stairs and maneuver in a wide variety of environments during activities of daily lives at reasonable metabolic costs.