Immediate Effects of Transcutaneous Spinal Cord Stimulation on Motor Function in Chronic, Sensorimotor Incomplete Spinal Cord Injury

Deficient ankle control after incomplete spinal cord injury (iSCI) often accentuates walking impairments. Transcutaneous electrical spinal cord stimulation (tSCS) has been shown to augment locomotor activity after iSCI, presumably due to modulation of spinal excitability. However, the effects of possible excitability modulations induced by tSCS on ankle control have not yet been assessed. This study investigated the immediate (i.e., without training) effects during single-sessions of tonic tSCS on ankle control, spinal excitability, and locomotion in ten individuals with chronic, sensorimotor iSCI (American Spinal Injury Association Impairment Scale D). Participants performed rhythmic ankle movements (dorsi- and plantar flexion) at a given rate, and irregular ankle movements following a predetermined trajectory with and without tonic tSCS at 15 Hz, 30 Hz, and 50 Hz. In a subgroup of eight participants, the effects of tSCS on assisted over-ground walking were studied. Furthermore, the activity of a polysynaptic spinal reflex, associated with spinal locomotor networks, was investigated to study the effect of the stimulation on the dedicated spinal circuitry associated with locomotor function. Tonic tSCS at 30 Hz immediately improved maximum dorsiflexion by +4.6° ± 0.9° in the more affected lower limb during the rhythmic ankle movement task, resulting in an increase of +2.9° ± 0.9° in active range of motion. Coordination of ankle movements, assessed by the ability to perform rhythmic ankle movements at a given target rate and to perform irregular movements according to a trajectory, was unchanged during stimulation. tSCS at 30 Hz modulated spinal reflex activity, reflected by a significant suppression of pathological activity specific to SCI in the assessed polysynaptic spinal reflex. During walking, there was no statistical group effect of tSCS. In the subgroup of eight assessed participants, the three with the lowest as well as the one with the highest walking function scores showed positive stimulation effects, including increased maximum walking speed, or more continuous and faster stepping at a self-selected speed. Future studies need to investigate if multiple applications and individual optimization of the stimulation parameters can increase the effects of tSCS, and if the technique can improve the outcome of locomotor rehabilitation after iSCI.

Comparison of Soleus H-Reflexes in Two Groups of Individuals With Motor Incomplete Spinal Cord Injury Walking With and Without a Walker

Objective: To compare phase- and task-dependent H-reflex modulation in standing and walking in 2 spinal cord injury (SCI) groups with and without a walker. Methods: Fourteen subjects with American Spinal Injury Association Impairment Scale D SCI (40±10 years) participated. Tibial nerve was stimulated to evoke 15 H-reflexes (at M-wave 7%-13% of maximum-M). Results: H-reflex was greater in the walker group during stance (but not standing/swing). Conclusion: Differences in H-reflex modulation between groups walking with and without a walker may be explained by sensory mechanism that enhances central excitation, difference in motor activation levels between groups, and other complex mechanisms that influence balance or stability.

Ankle voluntary movement enhancement following robotic-assisted locomotor training in spinal cord injury

BACKGROUND

In incomplete spinal cord injury (iSCI), sensorimotor impairments result in severe limitations to ambulation. To improve walking capacity, physical therapies using robotic-assisted locomotor devices, such as the Lokomat, have been developed. Following locomotor training, an improvement in gait capabilities-characterized by increases in the over-ground walking speed and endurance-is generally observed in patients. To better understand the mechanisms underlying these improvements, we studied the effects of Lokomat training on impaired ankle voluntary movement, known to be an important limiting factor in gait for iSCI patients.

METHODS

Fifteen chronic iSCI subjects performed twelve 1-hour sessions of Lokomat training over the course of a month. The voluntary movement was qualified by measuring active range of motion, maximal velocity peak and trajectory smoothness for the spastic ankle during a movement from full plantar-flexion (PF) to full dorsi-flexion (DF) at the patient's maximum speed. Dorsi- and plantar-flexor muscle strength was quantified by isometric maximal voluntary contraction (MVC). Clinical assessments were also performed using the Timed Up and Go (TUG), the 10-meter walk (10MWT) and the 6-minute walk (6MWT) tests. All evaluations were performed both before and after the training and were compared to a control group of fifteen iSCI patients.

RESULTS

After the Lokomat training, the active range of motion, the maximal velocity, and the movement smoothness were significantly improved in the voluntary movement. Patients also exhibited an improvement in the MVC for their ankle dorsi- and plantar-flexor muscles. In terms of functional activity, we observed an enhancement in the mobility (TUG) and the over-ground gait velocity (10MWT) with training. Correlation tests indicated a significant relationship between ankle voluntary movement performance and the walking clinical assessments.

CONCLUSIONS

The improvements of the kinematic and kinetic parameters of the ankle voluntary movement, and their correlation with the functional assessments, support the therapeutic effect of robotic-assisted locomotor training on motor impairment in chronic iSCI.

Comparison of the effects of solid versus hinged ankle foot orthoses on select temporal gait parameters in patients with incomplete spinal cord injury during treadmill walking

BACKGROUND

Ankle foot orthoses (AFOs) are usually used for patients with incomplete spinal cord injury (ISCI) to provide support in walking.

OBJECTIVES

The aim of this study was to compare the effect of AFOs, with and without ankle hinges, on specific gait parameters during treadmill training by subjects with ISCI.

STUDY DESIGN

Quasi-experimental.

METHODS

Five patients with ISCI at the thoracic level participated in this study. Gait evaluation was performed when walking 1) barefoot 2) wearing a solid AFO and 3) wearing a hinged AFO.

RESULTS

The mean step length when walking barefoot was 26.3 ± 16.37 cm compared to 31.3 ± 17.27 cm with a solid AFO and 28.5 ± 15.86 cm with a hinged AFO. The mean cadence for walking barefoot was 61.59 ± 25.65 steps/min. compared to 50.94 ± 22.36 steps/min. with a solid AFO and 56.25 ± 24.44 steps/min with a hinged AFO. Significant differences in cadence and step length during walking were only demonstrated between the barefoot condition and when wearing a solid AFO. Significant difference was not observed between conditions in mean of ankle range of motion.

CONCLUSION

The solid AFO was the only condition which improved cadence and step length in patients during ISCI gait training. Clinical relevance A solid AFO could be used permanently to compensate for impaired ankle function or it could be used while retraining stepping.

Soleus H-reflex modulation after motor incomplete spinal cord injury: effects of body position and walking speed

OBJECTIVE

To examine position-dependent (semireclined to standing) and walking speed-dependent soleus H-reflex modulation after motor incomplete spinal cord injury (SCI).

PARTICIPANTS

Twenty-six patients with motor incomplete SCI (mean: 45 +/- 15 years) and 16 noninjured people (mean: 38 +/- 14 years).

METHODS

Soleus H-reflexes were evoked by tibial nerve stimulation. Patients were tested in semireclined and standing positions (experiment 1) and in midstance and midswing positions (experiment 2).

RESULTS

H-reflexes were significantly greater after SCI in all positions compared with noninjured people (P < 0.05). Position-dependent modulation from semireclined to standing (normally observed in noninjured people) was absent after SCI. In SCI patients, H-reflex modulation was not significantly different at 1.2 m/s compared with 0.6 m/s treadmill walking speed; in noninjured people, H-reflex modulation was significantly greater at 1.2 m/s compared with 0.6 m/s treadmill walking speed. There was a significant positive correlation between modified Ashworth scores, a clinical measure of spasticity and soleus H-reflex amplitudes tested in all positions. A significant negative correlation was also found between H-reflexes in standing and midstance positions and the amount of assistance patients required to walk.

CONCLUSIONS

An improvement in position-dependent and walking speed-dependent reflex modulation after SCI may indicate functional recovery. Future studies will use H-reflex testing to track changes as a result of therapeutic interventions.

Stepping with an ankle foot orthosis re-examined: a mechanical perspective for clinical decision making

BACKGROUND

Ankle foot orthoses are used to stabilize the ankle joint and aid toe clearance during stepping in persons after incomplete spinal cord injury. However, little is known about kinematics and kinetics of stepping with an orthosis during the transition from stance-to-swing and swing-to-stance. We intended to examine if an ankle foot orthosis impeded or facilitated optimal ankle, knee and hip joint kinematics, kinetics and spatiotemporal parameters during the transition phases of normal walking.

METHODS

Fourteen healthy participants walked on a split-belt instrumented treadmill with and without a posterior leaf spring ankle foot orthosis at 1.2m/s. Three dimensional motion data and ground reaction forces were captured during 30-second trials of steady state walking.

FINDINGS

During stance-to-swing, the orthosis significantly decreased hip extension [8.6 (5.5) to 6.7 (5.5) degrees, P=0.001], ankle plantarflexion [19.4 (5.7) to 12.0 (5.2) degrees, P<0.001] and plantarflexor power [0.18 (0.03) to 0.15 (0.03) watts/body weight, P<0.001]. During swing-to-stance, the orthosis significantly increased hip flexion [32.7 (4.7) to 35.6 (5.1) degrees, P=0.028] and ankle plantarflexion [8.4 (3.5) to 10.9 (4.7) degrees, P<0.001] and decreased loading rate [0.06 (0.01) to 0.05 (0.01) N/kg, P=0.018] and braking force [0.16 (0.02) to 0.15 (0.02) N/kg, P=0.013]. Double limb support time increased significantly with the orthosis [0.19 (0.02) to 0.22 (0.03) seconds, P<0.000].

INTERPRETATION

An ankle foot orthosis affected joint kinematics and kinetics during the transition from stance-to-swing and vice-versa. The use of orthosis to improve transition phase kinematics and kinetics in individuals with incomplete spinal cord injury warrants assessment.

Reliability of soleus H-reflexes in standing and walking post-incomplete spinal cord injury

OBJECTIVE

To establish the reliability of soleus H-reflex in individuals with incomplete spinal cord injury (SCI) during the standing and the swing and stance phases of overground walking.

METHODS

Fourteen SCI (40 +/- 10 years) and eight noninjured subjects (32 +/- 9 years) participated. The noninjured and SCI subjects walked at self-selected speed overground. H-reflexes in the soleus muscle (at M-wave 7%-13% maximum-M) were tested on two separate days by stimulating the tibial nerve. Intraclass correlation coefficients (two-way mixed model-ICC (1, 2)) and standard error of measurement (SEM) were calculated.

RESULTS

Relative reliability of the H-reflexes was good to excellent; intra-class correlation coefficients (ICCs) ranged from 0.64-0.91 in noninjured and SCI subjects. SEM expressed as percentage of the mean H-reflex was 13%-62% in noninjured and 12%-18% in SCI individuals.

CONCLUSIONS

H-reflexes can be reliably assessed in standing and walking in post-SCI and noninjured subjects.

SIGNIFICANCE

H-reflexes can be reliably used in longitudinal studies to investigate mechanisms of recovery post-SCI.

Temporospatial and kinematic gait alterations during treadmill walking with body weight suspension

Our purpose was to analyze the effects of selected levels of body weight support (BWS) on lower extremity kinematics of normal subjects at a predetermined treadmill speed. Seventeen non-disabled volunteers walked on a treadmill at 1.25 ms(-1). Temporospatial and kinematic data were collected while various support levels were applied (Minimal, 10, 30, 50 and 70% BWS). Compared to 10% BWS, significant temporospatial and kinematic changes were induced by 50 and 70% BWS. Fewer differences were induced by 30% BWS compared to 10% BWS. We concluded that gait patterns of unimpaired subjects are significantly changed by 50 and 70% BWS.

Treadmill walking in incomplete spinal-cord-injured subjects: 1. Adaptation to changes in speed

Walking in spinal-cord-injured (SCI) subjects is usually achieved at a lower speed than in normal subjects.

STUDY DESIGN/METHODS

Time and distance parameters, angular displacements of lower limbs and electromyographic (EMG) activity were measured for seven normal and seven SCI subjects at several walking speeds. Analyses of variance were used for comparing groups and speeds.

OBJECTIVES

First, to measure the adaptability of SCI subjects' walking pattern to different speeds (0.1-1.0 m/s), and to compare it to that of normal subjects. Second, to characterize SCI subjects' walking pattern as compared to that of normal subjects at a matched treadmill speed (0.3 m/s).

SETTING

University-Based Human Gait Laboratory, Montreal, Canada.

RESULTS

SCI subjects' pattern adapted to a limited range of speeds. Longer cycle duration, flexed knee at foot contact, increased hip joint flexion at foot contact and during swing, and altered coordination of hip and knee joints were found for the SCI group. At all speeds, duration of muscle activity was longer in the SCI group and the increase in amplitude of soleus EMG activity at higher speeds was not specific to push-off. The importance of matching the walking speed of SCI and normal subjects in order to differentiate the features that are a consequence of SCI subjects' reduced walking speed rather than a direct consequence of the injury is demonstrated.

CONCLUSIONS

All SCI subjects could adapt to a narrow range of speeds and only three could reach the maximal tested speed. This limited maximal speed seems to be a consequence of SCI subjects having reached their limit in increasing stride length and not being able to increase stride frequency further. This limitation in increasing stride frequency is likely because of the altered neural drive.

SPONSORSHIP

Neuroscience Network of the Canadian Centre of Excellence.

A review of the adaptability and recovery of locomotion after spinal cord injury

Spinal cord injury (SCI) is associated with multiple motor problems leading to the alteration and limited adaptation in the walking and postural behavior. This review addresses recent findings on locomotor and postural adaptations after spinal cord injury. The adaptation of the locomotor behavior to behavioral goals and external constraints constitute important functional prerequisites in the recovery of locomotion after spinal cord injury. Functional prerequisites in locomotion include coping with changes in speed, slope obstacle, weight support, interaction with walking aids, energy consumption and attentional demands. Various treatment approaches such as locomotor training using body weight support (BWS) and functional electrical stimulation (FES) will be discussed, in the context of functional prerequisites necessary in the recovery of locomotion. Understanding locomotor and postural adaptations will lead to a better appreciation of the normal and dysfunctional mechanisms, and culminate eventually in the development of appropriate rehabilitation assessment and treatment strategies.

The special nature of human walking and its neural control

Walking the way we do is inherently unstable. Sophisticated neurological control systems are required to ensure that we progress and maintain our balance at the same time. Most of what is known about the functional organization of these neurological control systems is inferred from studies on animals. Here, I compare selected studies on the neural control of human walking with similar studies in reduced animal preparations. The simple monosynaptic reflex appears to be controlled by comparable mechanisms in walking cats and humans. However, peripheral feedback mechanisms suggested to contribute to the switch from stance to swing on the basis of experiments in reduced cat preparations have little influence during human walking. A cat whose spinal cord has been completely transected can be made to walk on a treadmill by drug injections, but such an immediate effect of pharmacological intervention is not seen in humans. However, there have been reports that pharmacological intervention can improve the walking of patients with incomplete spinal cord injury, especially when pharmacological treatment is combined with training.

Spinal transection increases the potency of clonidine on the tail-flick and hindlimb flexion reflexes

The effect of intrathecal clonidine on thermal nociception and hindlimb flexion was assessed in acute and chronic spinally transected rats. After an acute, 1-day spinalization, there was no change in the antinociceptive dose-response function to clonidine, relative to intact rats. However, there was a significant increase in potency 31 days after spinalization. Low doses of clonidine (0.25, 1, 4 and 20 microg) did not affect the nonnociceptive flexion reflex of acute spinal rats, but they elicited a dose-dependent response in chronic spinal rats. These data provide behavioral evidence of supersensitivity to alpha-adrenoceptor agonists in chronic spinal rats.

Functional community ambulation requirements in incomplete spinal cord injured subjects

STUDY DESIGN

A group of people with incomplete spinal cord injuries (SCI) were evaluated and compared with able-bodied individuals during several walking conditions.

OBJECTIVES

To evaluate the functional community ambulation and estimated energy expenditure in persons with incomplete SCI and able-bodied individuals.

METHODS

A list of criteria was used to evaluate functional community ambulation among participants. Physiological variables, such as the heart rate, oxygen uptake and the lactate concentration, were also measured.

RESULTS

Three of nine incomplete SCI subjects and all able-bodied subjects were able to meet all the criteria measured. The required velocity to safely cross an intersection was the criterion that the incomplete SCI group had the most difficulty reaching. The able-bodied subjects had a comfortable walking velocity twice that of the incomplete SCI subjects' preferred velocity. When walking at the same velocity (incomplete SCI subjects' preferred velocity), the incomplete SCI subjects had a rate of oxygen uptake 26% greater than the healthy subjects and were 200% less efficient. The lactate concentration also proved to be a useful tool when evaluating the incomplete SCI subjects' walking efficiency. The incomplete SCI subjects lactate concentration increased after walking at their preferred velocity, meaning that the anaerobic pathways were used to meet energy demands.

CONCLUSION

Rehabilitation centers should adapt their evaluation forms and increase their criteria requirements to more suitable criteria that are found in the SCI patient's community. The physiological cost should also be taken into consideration when evaluating the SCI patient's functional ambulation.

Spinal cord injury in small animals 2. Current and future options for therapy

Although there can be substantial spontaneous improvements in functional status after a spinal cord injury, therapeutic intervention is desirable in many patients to improve the degree of recovery. At present only decompressive surgery and the neuroprotective drug methylprednisolone sodium succinate are effective and in widespread clinical use. There are limitations to the efficacy of these therapies in some clinical cases and they cannot restore satisfactory functional status to all patients. Many drugs have been investigated experimentally to assess their potential to preserve injured tissue and promote functional recovery in clinically relevant settings, and several of them would be suitable for assessment in future veterinary clinical trials. In addition, experimental techniques designed to mould the response of the CNS to injury, by the promotion of axonal regeneration across the lesion and the encouragement of local sprouting of undamaged axons, have recently been successful, suggesting that effective therapy for even very severe spinal cord injury may soon be available.

Hindlimb locomotor and postural training modulates glycinergic inhibition in the spinal cord of the adult spinal cat

Adult spinal cats were trained initially to perform either bipedal hindlimb locomotion on a treadmill or full-weight-bearing hindlimb standing. After 12 wk of training, stepping ability was tested before and after the administration (intraperitoneal) of the glycinergic receptor antagonist, strychnine. Spinal cats that were trained to stand after spinalization had poor locomotor ability as reported previously, but strychnine administration induced full-weight-bearing stepping in their hindlimbs within 30-45 min. In the cats that were trained to step after spinalization, full-weight-bearing stepping occurred and was unaffected by strychnine. Each cat then was retrained to perform the other task for 12 wk and locomotor ability was retested. The spinal cats that were trained initially to stand recovered the ability to step after they received 12 wk of treadmill training and strychnine was no longer effective in facilitating their locomotion. Locomotor ability declined in the spinal cats that were retrained to stand and strychnine restored the ability to step to the levels that were acquired after the step-training period. Based on analyses of hindlimb muscle electromyographic activity patterns and kinematic characteristics, strychnine improved the consistency of the stepping and enhanced the execution of hindlimb flexion during full-weight-bearing step cycles in the spinal cats when they were trained to stand but not when they were trained to step. The present findings provide evidence that 1) the neural circuits that generate full-weight-bearing hindlimb stepping are present in the spinal cord of chronic spinal cats that can and cannot step; however, the ability of these circuits to interpret sensory input to drive stepping is mediated at least in part by glycinergic inhibition; and 2) these spinal circuits adapt to the specific motor task imposed, and that these adaptations may include modifications in the glycinergic pathways that provide inhibition.

Walking after spinal cord injury: evaluation, treatment, and functional recovery

OBJECTIVE

To present some recent developments and concepts emerging from both animal and human studies aimed at enhancing recovery of walking after spinal cord injury (SCI).

DATA SOURCES

Researchers in the field of restoration of walking after SCI, as well as references extracted from searches in the Medline computerized database.

STUDY SELECTION

Studies that reported outcome measures of walking for spinal cord injured persons with an incomplete motor function loss or cats with either a complete or incomplete spinal section.

DATA EXTRACTION

Data were extracted and validity was assessed by the authors.

DATA SYNTHESIS

This review shows that a multitude of interventions--mechanical, electrical, or pharmacologic--can increase the walking abilities of persons with SCI who have incomplete motor function loss.

CONCLUSIONS

A comprehensive evaluation of walking behavior requires tasks involving the different control variables. This comprehensive evaluation can be used to characterize the process of recovery of walking as well as the effectiveness of various treatments.

Does neurorehabilitation play a role in the recovery of walking in neurological populations?

This review demonstrates that neurorehabilitation approaches, based on recent neuroscience findings, can enhance locomotor recovery after a spinal cord injury or stroke. Findings are presented from more than 20 clinical studies conducted by numerous research groups on the effect of locomotor training using either body weight support (BWS), functional electrical stimulation (FES), pharmacological approaches or a combination of them. Among the approaches, only BWS-assisted locomotor training has been demonstrated to have a greater effect than conventional or locomotor training alone. However, when study results were combined and weighted for the number of subjects, the results indicated that there is a gradient of effects from small changes with the immediate application of FES or BWS to larger changes when locomotor training is combined with FES or BWS or pharmacological approaches. The findings of these studies suggest that these neurorehabilitation approaches do play a role in the recovery of walking in subjects with spinal cord injury or stroke. Several factors contribute to the potential for recovery including the site, etiology, and chronicity of the injury, as well as the type, duration, and specificity of the intervention and whether interventions are combined. Furthermore, how these neurorehabilitation approaches may take advantage of the plasticity process following neurological lesion is also discussed.

Effects of intrathecal alpha1- and alpha2-noradrenergic agonists and norepinephrine on locomotion in chronic spinal cats

Noradrenergic drugs, acting on alpha adrenoceptors, have been found to play an important role in the initiation and modulation of locomotor pattern in adult cats after spinal cord transection. There are at least two subtypes of alpha adrenoceptors, alpha1 and alpha2 adrenoceptors. The aim of this study was to investigate the effects of selective alpha1 and alpha2 agonists in the initiation and modulation of locomotion in adult chronic cats in the early and late stages after complete transection at T13. Five cats, chronically implanted with an intrathecal cannula and electromyographic (EMG) electrodes were used in this study. Noradrenergic drugs including alpha2 agonists (clonidine, tizanidine, and oxymetazoline) and an antagonist, yohimbine, one alpha1 agonist (methoxamine), and a blocker, prazosin, as well as norepinephrine were injected intrathecally. EMG activity synchronized to video images of the hindlimbs were recorded before and after each drug injection. The results show differential effects of alpha1 and alpha2 agonists in the initiation of locomotion in early spinal cats (i.e., in the first week or so when there is no spontaneous locomotion) and in the modulation of locomotion and cutaneous reflexes in the late-spinal cats (i.e., when cats have recovered spontaneous locomotion). In early spinal cats, all three alpha2 agonists were found to initiate locomotion, although their action had a different time course. The alpha1 agonist methoxamine induced bouts of nice locomotor activity in three spinal cats some hours after injection but only induced sustained locomotion in one cat in which the effects were blocked by the alpha1 antagonist prazosin. In late spinal cats, although alpha2 agonists markedly increased the cycle duration and flexor muscle burst duration and decreased the weight support or extensor activity (effects blocked by an alpha2 antagonist, yohimbine), alpha1 agonist increased the weight support and primarily the extensor activity of the hindlimbs without markedly changing the timing of the step cycle. Although alpha2 agonists, especially clonidine, markedly reduced the cutaneous excitability and augmented the foot drag, the alpha1 agonist was found to increase the cutaneous reflex excitability. This is in line with previously reported differential effects of activation of the two receptors on motoneuron excitability and reflex transmission. Noradrenaline, the neurotransmitter itself, increased the cycle duration and at the same time retained the cutaneous excitability, thus exerting both alpha1 and alpha2 effects. This work therefore suggests that different subclasses of noradrenergic drugs could be used to more specifically target aspects of locomotor deficits in patients after spinal injury or diseases.