A Muscle-First, Electromechanical Hybrid Gait Restoration System in People With Spinal Cord Injury.

The development of a hybrid system for people with spinal cord injuries is described. The system includes implanted neural stimulation to activate the user's otherwise paralyzed muscles, an exoskeleton with electromechanical actuators at the hips and knees, and a sensory and control system that integrates both components. We are using a muscle-first approach: The person's muscles are the primary motivator for his/her joints and the motors provide power assistance. This design philosophy led to the development of high efficiency, low friction joint actuators, and feed-forward, burst-torque control. The system was tested with two participants with spinal cord injury (SCI) and unique implanted stimulation systems. Torque burst addition was found to increase gait speed. The system was found to satisfy the main design requirements as laid out at the outset.

Walking after incomplete spinal cord injury with an implanted neuromuscular electrical stimulation system and a hinged knee replacement: a single-subject study.

STUDY DESIGN: Single-subject repeated measures study. OBJECTIVES: Neuromuscular electrical stimulation (NMES) can enhance walking for people with partial paralysis from incomplete spinal cord injury (iSCI). This single-subject study documents an individual's experience who both received an experimental implanted NMES system and underwent clinical bilateral hinged total knee arthroplasty (TKA). She walked in the community with knee pain prior to either intervention. Walking performance improved with an implanted NMES system. Knee pain and instability continued to worsen over time and eventually required TKA. This study evaluates the effects of these interventions. SETTING: Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland OH, USA. METHODS: The differential and combined effects of NMES and hinged knee replacement were assessed in terms of walking speed, toe clearance, knee angle, and participant perceptions with and without stimulation assistance both before and after TKA. RESULTS: The combined approach both reduced pain and restored walking ability to levels achieved prior to developing significant knee pain that prevented walking without NMES. There was an interaction effect between NMES and TKA on walking speed. Toe clearance consistently improved with stimulation assistance and TKA prevented significant knee hyperextension. The greatest impact was on endurance. Knee replacement re-enabled long distance walking with the addition of stimulation again more than doubling her maximum walking distance from 214 to 513 m. CONCLUSIONS: These data support further research of combined implantable interventions that may benefit people with iSCI. Furthermore, joint laxity and pain may not necessarily be contraindications to NMES if addressed with conventional clinical treatments.

Oxygen Consumption While Walking With Multijoint Neuromuscular Electrical Stimulation After Stroke.

This case study evaluated the effect of implanted multijoint neuromuscular electrical stimulation gait assistance on oxygen consumption relative to walking without neuromuscular electrical stimulation after stroke. The participant walked slowly with an asymmetric gait pattern after stroke. He completed repeated 6-min walk tests at a self-selected walking speed with and without hip, knee, and ankle stimulation assistance. His walking speed with neuromuscular electrical stimulation more than doubled from 0.28 ± 0.01 m/sec to 0.58 ± 0.04 m/sec, whereas average step length and cadence increased by 0.12 m and 24 steps/min, respectively. As a result, energy cost of walking with neuromuscular electrical stimulation decreased by 0.19 ml O2/kg per meter as compared with walking without stimulation while oxygen consumption increased by 1.1 metabolic equivalent of tasks (3.9 ml O2/kg per minute). These metabolic demands are similar to those reported for stroke survivors capable of walking at equivalent speeds without stimulation, suggesting the increase in oxygen consumption and decreased energy cost result from improved efficiency of faster walking facilitated by neuromuscular electrical stimulation. Although the effect of neuromuscular electrical stimulation on gait economy has implications for community walking within the user's metabolic reserves, this case study's results should be interpreted with caution and the hypothesis that multijoint neuromuscular electrical stimulation improves metabolic efficiency should be tested in a wide population of stroke survivors with varied deficits.

Long-Term Performance and User Satisfaction With Implanted Neuroprostheses for Upright Mobility After Paraplegia: 2- to 14-Year Follow-Up.

OBJECTIVE: To quantify the long-term (>2y) effects of lower extremity (LE) neuroprostheses (NPs) for standing, transfers, stepping, and seated stability after spinal cord injury. DESIGN: Single-subject design case series with participants acting as their own concurrent controls, including retrospective data review. SETTING: Hospital-based clinical biomechanics laboratory with experienced (>20y in the field) research biomedical engineers, a physical therapist, and medical monitoring review. PARTICIPANTS: Long-term (6.2±2.7y) at-home users (N=22; 19 men, 3 women) of implanted NPs for trunk and LE function with chronic (14.4±7.1y) spinal cord injury resulting in full or partial paralysis. INTERVENTIONS: Technical and clinical performance measurements, along with user satisfaction surveys. MAIN OUTCOME MEASURES: Knee extension moment, maximum standing time, body weight supported by lower extremities, 3 functional standing tasks, 2 satisfaction surveys, NP usage, and stability of implanted components. RESULTS: Stimulated knee extension strength and functional capabilities were maintained, with 94% of implant recipients reporting being very or moderately satisfied with their system. More than half (60%) of the participants were still using their implanted NPs for exercise and function for >10min/d on nearly half or more of the days monitored; however, maximum standing times and percentage body weight through LEs decreased slightly over the follow-up interval. Stimulus thresholds were uniformly stable. Six-year survival rates for the first-generation implanted pulse generator (IPG) and epimysial electrodes were close to 90%, whereas those for the second-generation IPG along with the intramuscular and nerve cuff electrodes were >98%. CONCLUSIONS: Objective and subjective measures of the technical and clinical performances of implanted LE NPs generally remained consistent for 22 participants after an average of 6 years of unsupervised use at home. These findings suggest that implanted LE NPs can provide lasting benefits that recipients value.

Effect of exoskeletal joint constraint and passive resistance on metabolic energy expenditure: Implications for walking in paraplegia.

An important consideration in the design of a practical system to restore walking in individuals with spinal cord injury is to minimize metabolic energy demand on the user. In this study, the effects of exoskeletal constraints on metabolic energy expenditure were evaluated in able-bodied volunteers to gain insight into the demands of walking with a hybrid neuroprosthesis after paralysis. The exoskeleton had a hydraulic mechanism to reciprocally couple hip flexion and extension, unlocked hydraulic stance controlled knee mechanisms, and ankles fixed at neutral by ankle-foot orthoses. These mechanisms added passive resistance to the hip (15 Nm) and knee (6 Nm) joints while the exoskeleton constrained joint motion to the sagittal plane. The average oxygen consumption when walking with the exoskeleton was 22.5 ± 3.4 ml O2/min/kg as compared to 11.7 ± 2.0 ml O2/min/kg when walking without the exoskeleton at a comparable speed. The heart rate and physiological cost index with the exoskeleton were at least 30% and 4.3 times higher, respectively, than walking without it. The maximum average speed achieved with the exoskeleton was 1.2 ± 0.2 m/s, at a cadence of 104 ± 11 steps/min, and step length of 70 ± 7 cm. Average peak hip joint angles (25 ± 7°) were within normal range, while average peak knee joint angles (40 ± 8°) were less than normal. Both hip and knee angular velocities were reduced with the exoskeleton as compared to normal. While the walking speed achieved with the exoskeleton could be sufficient for community ambulation, metabolic energy expenditure was significantly increased and unsustainable for such activities. This suggests that passive resistance, constraining leg motion to the sagittal plane, reciprocally coupling the hip joints, and weight of exoskeleton place considerable limitations on the utility of the device and need to be minimized in future designs of practical hybrid neuroprostheses for walking after paraplegia.

A muscle-driven approach to restore stepping with an exoskeleton for individuals with paraplegia.

BACKGROUND: Functional neuromuscular stimulation, lower limb orthosis, powered lower limb exoskeleton, and hybrid neuroprosthesis (HNP) technologies can restore stepping in individuals with paraplegia due to spinal cord injury (SCI). However, a self-contained muscle-driven controllable exoskeleton approach based on an implanted neural stimulator to restore walking has not been previously demonstrated, which could potentially result in system use outside the laboratory and viable for long term use or clinical testing. In this work, we designed and evaluated an untethered muscle-driven controllable exoskeleton to restore stepping in three individuals with paralysis from SCI. METHODS: The self-contained HNP combined neural stimulation to activate the paralyzed muscles and generate joint torques for limb movements with a controllable lower limb exoskeleton to stabilize and support the user. An onboard controller processed exoskeleton sensor signals, determined appropriate exoskeletal constraints and stimulation commands for a finite state machine (FSM), and transmitted data over Bluetooth to an off-board computer for real-time monitoring and data recording. The FSM coordinated stimulation and exoskeletal constraints to enable functions, selected with a wireless finger switch user interface, for standing up, standing, stepping, or sitting down. In the stepping function, the FSM used a sensor-based gait event detector to determine transitions between gait phases of double stance, early swing, late swing, and weight acceptance. RESULTS: The HNP restored stepping in three individuals with motor complete paralysis due to SCI. The controller appropriately coordinated stimulation and exoskeletal constraints using the sensor-based FSM for subjects with different stimulation systems. The average range of motion at hip and knee joints during walking were 8.5°-20.8° and 14.0°-43.6°, respectively. Walking speeds varied from 0.03 to 0.06 m/s, and cadences from 10 to 20 steps/min. CONCLUSIONS: A self-contained muscle-driven exoskeleton was a feasible intervention to restore stepping in individuals with paraplegia due to SCI. The untethered hybrid system was capable of adjusting to different individuals' needs to appropriately coordinate exoskeletal constraints with muscle activation using a sensor-driven FSM for stepping. Further improvements for out-of-the-laboratory use should include implantation of plantar flexor muscles to improve walking speed and power assist as needed at the hips and knees to maintain walking as muscles fatigue.

Feasibility of Restoring Walking in Multiple Sclerosis with Multichannel Implanted Electrical Stimulation.

A patient with multiple sclerosis-related gait dysfunction was followed over the course of his disease. Despite aggressive treatment, he developed significant weakness in ankle dorsiflexors and hip and knee flexors and was no longer capable of consistently taking a step on his own. With electrical stimulation of hip and knee flexors and ankle dorsiflexors using implanted electrodes, he was able to consistently walk short distances as far as 30 m, thus significantly improving his Expanded Disability Status Scale score. This case study supports further exploration into the potential benefits of an implanted pulse generator to ameliorate gait dysfunction and improve quality of life for people with multiple sclerosis.

Improving Walking with an Implanted Neuroprosthesis for Hip, Knee, and Ankle Control After Stroke.

OBJECTIVE: The objective of this work was to quantify the effects of a fully implanted pulse generator to activate or augment actions of hip, knee, and ankle muscles after stroke. DESIGN: The subject was a 64-year-old man with left hemiparesis resulting from hemorrhagic stroke 21 months before participation. He received an 8-channel implanted pulse generator and intramuscular stimulating electrodes targeting unilateral hip, knee, and ankle muscles on the paretic side. After implantation, a stimulation pattern was customized to assist with hip, knee, and ankle movement during gait.The subject served as his own concurrent and longitudinal control with and without stimulation. Outcome measures included 10-m walk and 6-minute timed walk to assess gait speed, maximum walk time, and distance to measure endurance, and quantitative motion analysis to evaluate spatial-temporal characteristics. Assessments were repeated under 3 conditions: (1) volitional walking at baseline, (2) volitional walking after training, and (3) walking with stimulation after training. RESULTS: Volitional gait speed improved with training from 0.29 m/s to 0.35 m/s and further increased to 0.72 m/s with stimulation. Most spatial-temporal characteristics improved and represented more symmetrical and dynamic gait. CONCLUSIONS: These data suggest that a multijoint approach to implanted neuroprostheses can provide clinically relevant improvements in gait after stroke. TO CLAIM CME CREDITS: Complete the self-assessment activity and evaluation online at http://www.physiatry.org/JournalCME CME OBJECTIVES:: Upon completion of this article, the reader should be able to do the following: (1) Describe the rationale for evaluating a multijoint implanted neuroprosthesis to improvewalkingafter stroke; (2)Understand the study design and conclusions that can be inferred as a result of the design; and (3) Discuss the statistical significance and clinical relevance of changes between (a) volitional walking at baseline, (b) volitional walking after training, and (c) walking with stimulation after training. LEVEL: Advanced ACCREDITATION:: The Association of Academic Physiatrists is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The Association of Academic Physiatrists designates this activity for a maximum of 1.5 AMA PRA Category 1 Credit(s)™. Physicians should only claim credit commensurate with the extent of their participation in the activity.

Improving stand-to-sit maneuver for individuals with spinal cord injury.

BACKGROUND: Users of neuroprostheses employing electrical stimulation (ES) generally complete the stand-to-sit (STS) maneuver with high knee angular velocities, increased upper limb support forces, and high peak impact forces at initial contact with the chair. Controlling the knee during STS descent is challenging in individuals with spinal cord injury (SCI) due to the decreasing joint moment available with increased knee angle in response to ES. METHODS: The goal of this study was to investigate the effects of incorporating either (1) a coupling mechanism that coordinates hip and knee flexion or (2) a mechanism that damps knee motion to keep the knee angular velocity constant during the STS transition. The coupling and damping were achieved by hydraulic orthotic mechanisms. Two subjects with SCI were enrolled and each served as their own controls when characterizing the performance of each mechanism during STS as compared to stimulation alone. Outcome measures such as hip-knee angle, knee angular velocity, upper limb support force, and impact force were analyzed to determine the effectiveness of the two mechanisms in providing controlled STS. RESULTS: The coordination between the hip and knee joints improved with each orthotic mechanism. The damping and hip-knee coupling mechanisms caused the hip and knee joint ratios of 1:1.1 and 1:0.99, respectively, which approached the 1:1 coordination ratio observed in nondisabled individuals during STS maneuver. The knee damping mechanism provided lower (p < 0.001) and a more constant knee angular velocity than the hip-knee coupling mechanism over the knee range of motion. Both the coupling and damping mechanisms were similarly effective at reducing upper limb support forces by 70 % (p < 0.001) and impact force by half (p ≤ 0.001) as compared to sitting down with stimulation alone. CONCLUSIONS: Orthoses imposing simple kinematic constraints, such as 1:1 hip-knee coupling or knee damping, can normalize upper limb support forces, peak knee angular velocity, and peak impact force during the STS maneuvers.

A stimulation-driven exoskeleton for walking after paraplegia.

An untethered version of a stimulation-driven exoskeleton was evaluated for its ability to restore walking after paralysis from spinal cord injury. The hybrid neuroprosthesis (HNP) combined a passive variable-constraint exoskeleton for stability and support with functional neuromuscular stimulation (FNS) to contract the paralyzed muscles to drive limb movement. This self-contained HNP was operated by an onboard controller that sampled sensor signals, generated appropriate commands to both the exoskeletal constraints and integrated stimulator, and transmitted data wirelessly via Bluetooth to an off-board computer for real-time monitoring and recording for offline analysis. The subject selected the desired function (i.e. standing up, stepping, or sitting down) by means of a wireless finger switch that communicated with the onboard controller. Within the stepping function, a gait event detector supervisory controller transitioned between the different phases of gait such as double stance, swing, and weight acceptance based on signals from sensors incorporated into the exoskeleton. The different states of the control system governed the locking and unlocking of the exoskeletal hip and knee joints as well as the stimulation patterns activating hip and knee flexor or extensor muscles at the appropriate times and intensities to enable stepping. This study was one of our first successful implementations of the self-contained "muscle-first" HNP and successfully restored gait to an individual with motor complete mid-thoracic paraplegia.

Accelerometer-based step initiation control for gait-assist neuroprostheses.

Electrical activation of paralyzed musculature can generate or augment joint movements required for walking after central nervous system trauma. Proper timing of stimulation relative to residual volitional control is critical to usefully affecting ambulation. This study evaluates three-dimensional accelerometers and customized algorithms to detect the intent to step from voluntary movements to trigger stimulation during walking in individuals with significantly different etiologies, mobility limitations, manual dexterities, and walking aids. Three individuals with poststroke hemiplegia or partial spinal cord injury exhibiting varying gait deficits were implanted with multichannel pulse generators to provide joint motions at the hip, knee, and ankle. An accelerometer integrated into the external control unit was used to detect heel strike or walker movement, and wireless accelerometers were used to detect crutch strike. Algorithms were developed for each sensor location to detect intent to step to progress through individualized stimulation patterns. Testing these algorithms produced detection accuracies of at least 90% on both level ground and uneven terrain. All participants use their accelerometer-triggered implanted gait systems in the community; the validation/system testing was completed in the hospital. The results demonstrated that safe, reliable, and convenient accelerometer-based step initiation can be achieved regardless of specific gait deficits, manual dexterities, and walking aids.

Feasibility of a Hydraulic Power Assist System for Use in Hybrid Neuroprostheses.

Feasibility of using pressurized hydraulic fluid as a source of on-demand assistive power for hybrid neuroprosthesis combining exoskeleton with functional neuromuscular stimulation was explored. Hydraulic systems were selected as an alternative to electric motors for their high torque/mass ratio and ability to be located proximally on the exoskeleton and distribute power distally to assist in moving the joints. The power assist system (PAS) was designed and constructed using off-the-shelf components to test the feasibility of using high pressure fluid from an accumulator to provide assistive torque to an exoskeletal hip joint. The PAS was able to provide 21 Nm of assistive torque at an input pressure of 3171 kPa with a response time of 93 ms resulting in 32° of hip flexion in an able-bodied test. The torque output was independent of initial position of the joint and was linearly related to pressure. Thus, accumulator pressure can be specified to provide assistive torque as needed in exoskeletal devices for walking or stair climbing beyond those possible either volitionally or with electrical stimulation alone.

Powered Lower-Limb Exoskeletons to Restore Gait for Individuals with Paraplegia - a Review.

Individuals with paraplegia due to spinal cord injury rank restoration of walking high on the list of priorities to improving their quality of life. Powered lower-limb exoskeleton technology provides the ability to restore standing up, sitting down, and walking movements for individuals with paraplegia. The robotic exoskeletons generally have electrical motors located at the hip and knee joint centers, which move the wearers' lower limbs through the appropriate range of motion for gait according to control systems using either trajectory control or impedance control. Users of exoskeletons are able to walk at average gait speeds of 0.26 m/s and distances ranging between 121-171 m. However, the achieved gait speeds and distances fall short of those required for full community ambulation (0.8 m/s and at least 230 m), restricting use of the devices to limited community use with stand-by assist or supervised rehabilitation settings. Improvement in the gait speed and distance may be achievable by combining a specially designed powered exoskeleton with neuromuscular stimulation technologies resulting in a hybrid system that fully engages the user and achieves the necessary requirements to ambulate in the community environment with benefits of muscle contraction.

Forward stair descent with hybrid neuroprosthesis after paralysis: Single case study demonstrating feasibility.

The ability to negotiate stairs is important for community access and independent mobility but requires more effort and strength than level walking. For this reason, previous attempts to utilize functional neuromuscular stimulation (FNS) to restore stair navigation after spinal cord injury (SCI) have had limited success and are not readily generalizable. Stair descent is particularly challenging because it requires energy absorption via eccentric muscle contractions, a task not easily accomplished with FNS. This article presents the design and initial testing of a hybrid neuroprosthesis with a variable impedance knee mechanism (VIKM-HNP) for stair descent. Using a 16-channel percutaneous FNS system, a muscle activation pattern was synthesized to descend stairs with the VIKM-HNP in a step-by-step fashion. A finite state control system was implemented to deactivate knee extensor stimulation and utilize the VIKM-HNP to absorb energy and regulate descent speed. Feasibility testing was performed on one individual with complete thoracic-level SCI. Stair descent was achieved with maximum upper-limb forces of less than 45% body weight compared with previously reported value of 70% with FNS only. The experiments also provided insight into design requirements for future hybrid systems for stair navigation, the implications of which are discussed.

Functional electrical stimulation and spinal cord injury.

Spinal cord injuries (SCI) can disrupt communications between the brain and the body, resulting in loss of control over otherwise intact neuromuscular systems. Functional electrical stimulation (FES) of the central and peripheral nervous system can use these intact neuromuscular systems to provide therapeutic exercise options to allow functional restoration and to manage medical complications following SCI. The use of FES for the restoration of muscular and organ functions may significantly decrease the morbidity and mortality following SCI. Many FES devices are commercially available and should be considered as part of the lifelong rehabilitation care plan for all eligible persons with SCI.

Sensor-based hip control with hybrid neuroprosthesis for walking in paraplegia.

The objectives of this study were to test whether a hybrid neuroprosthesis (HNP) with an exoskeletal variable-constraint hip mechanism (VCHM) combined with a functional neuromuscular stimulation (FNS) controller can maintain upright posture with less upper-limb support and improve gait speed as compared with walking with either an isocentric reciprocating gait orthosis (IRGO) or FNS only. The results show that walking with the HNP significantly reduced forward lean in FNS-only walking and the maximum upper-limb forces by 42% and 19% as compared with the IRGO and FNS-only gait, respectively. Walking speed increased significantly with VCHM as compared with 1:1 reciprocal coupling and by 15% when using the sensor-based FNS controller as compared with HNP with fixed baseline stimulation without the controller active.

Understanding stand-to-sit maneuver: implications for motor system neuroprostheses after paralysis.

Standing up, standing, and walking functions can be restored to people with spinal cord injury by contracting the paralyzed hip, knee, and ankle muscles with electrical stimulation. Restoring these functions using electrical stimulation requires controlled activation to provide coordinated movements. However, the stand-to-sit (STS) maneuver involves eccentric contractions of the quadriceps to control lowering of the body to the seated position, which is difficult to achieve with stimulation alone and presents unique challenges to lower-limb neuroprostheses. In this study, we examined the biomechanics of the STS maneuver in five nondisabled individuals and five users of an implanted neuroprosthesis. Neuroprosthesis users relied heavily on their upper limbs during STS, with peak supporting forces approximately 25% body weight, and exhibited an average vertical acceleration at the impact six times higher than that of the nondisabled subjects (p < 0.001). Sitting with stimulation resulted in impact forces at initial contact with the seating surface averaging 1.4 times body weight and representing an average of twice the impact forces of the nondisabled subjects (p < 0.001). These results indicate a need for additional interventions to better control descent, minimize impact, and gently transition from standing to sitting to achieve a more natural movement and reduce the risk of injury.

Stance controlled knee flexion improves stimulation driven walking after spinal cord injury.

BACKGROUND: Functional neuromuscular stimulation (FNS) restores walking function after paralysis from spinal cord injury via electrical activation of muscles in a coordinated fashion. Combining FNS with a controllable orthosis to create a hybrid neuroprosthesis (HNP) has the potential to extend walking distance and time by mechanically locking the knee joint during stance to allow knee extensor muscle to rest with stimulation turned off. Recent efforts have focused on creating advanced HNPs which couple joint motion (e.g., hip and knee or knee and ankle) to improve joint coordination during swing phase while maintaining a stiff-leg during stance phase. METHODS: The goal of this study was to investigate the effects of incorporating stance controlled knee flexion during loading response and pre-swing phases on restored gait. Knee control in the HNP was achieved by a specially designed variable impedance knee mechanism (VIKM). One subject with a T7 level spinal cord injury was enrolled and served as his own control in examining two techniques to restore level over-ground walking: FNS-only (which retained a stiff knee during stance) and VIKM-HNP (which allowed controlled knee motion during stance). The stimulation pattern driving the walking motion remained the same for both techniques; the only difference was that knee extensor stimulation was constant during stance with FNS-only and modulated together with the VIKM to control knee motion during stance with VIKM-HNP. RESULTS: Stance phase knee angle was more natural during VIKM-HNP gait while knee hyperextension persisted during stiff-legged FNS-only walking. During loading response phase, vertical ground reaction force was less impulsive and instantaneous gait speed was increased with VIKM-HNP, suggesting that knee flexion assisted in weight transfer to the leading limb. Enhanced knee flexion during pre-swing phase also aided flexion during swing, especially when response to stimulation was compromised. CONCLUSIONS: These results show the potential advantages of incorporating stance controlled knee flexion into a hybrid neuroprosthesis for walking. The addition of such control to FNS driven walking could also enable non-level walking tasks such as uneven terrain, slope navigation and stair descent where controlled knee flexion during weight bearing is critical.

Ambulation and spinal cord injury.

Walking is possible for many patients with a spinal cord injury. Avenues enabling walking include braces, robotics and FES. Among the benefits are improved musculoskeletal and mental health, however unrealistic expectations may lead to negative changes in quality of life. Use rigorous assessment standards to gauge the improvement of walking during the rehabilitation process, but also yearly. Continued walking after discharge may be limited by challenges, such as lack of accessibility in and outside the home, and complications, such as shoulder pain or injuries from falls. It is critical to determine the risks and benefits of walking for each patient.

Finite state control of a variable impedance hybrid neuroprosthesis for locomotion after paralysis.

We have previously reported on a novel variable impedance knee mechanism (VIKM). The VIKM was designed as a component of a hybrid neuroprosthesis to regulate knee flexion. The hybrid neuroprosthesis is a device that uses a controllable brace to support the body against collapse while stimulation provides power for movement. The hybrid neuroprosthesis requires a control system to coordinate the actions of the VIKM with the stimulation system; the development and evaluation of such a controller is presented. Brace mounted sensors and a baseline open loop stimulation pattern are utilized as control signals to activate the VIKM during stance phase while simultaneously modulating muscle stimulation in an on-off fashion. The objective is twofold: reduce the amount of stimulation necessary for walking while simultaneously restoring more biologically correct knee motion during stance using the VIKM. Custom designed hardware and software components were developed for controller implementation. The VIKM hybrid neuroprosthesis (VIKM-HNP) was evaluated during walking in one participant with thoracic level spinal cord injury. In comparison to walking with functional neuromuscular stimulation alone, the VIKM-HNP restored near normal stance phase knee flexion during loading response and pre-swing phases while decreasing knee extensor stimulation by up to 40%.