Recovery of Over-Ground Walking after Chronic Motor Complete Spinal Cord Injury.

Persons with motor complete spinal cord injury, signifying no voluntary movement or sphincter function below the level of injury but including retention of some sensation, do not recover independent walking. We tested intense locomotor treadmill training with weight support and simultaneous spinal cord epidural stimulation in four patients 2.5 to 3.3 years after traumatic spinal injury and after failure to improve with locomotor training alone. Two patients, one with damage to the mid-cervical region and one with damage to the high-thoracic region, achieved over-ground walking (not on a treadmill) after 278 sessions of epidural stimulation and gait training over a period of 85 weeks and 81 sessions over a period of 15 weeks, respectively, and all four achieved independent standing and trunk stability. One patient had a hip fracture during training. (Funded by the Leona M. and Harry B. Helmsley Charitable Trust and others; ClinicalTrials.gov number, NCT02339233 .).

Soleus H-reflex gain, threshold, and amplitude as function of body posture and load in spinal cord intact and injured subjects.

In this study, we established parameters of the soleus H-reflex excitability in response to changes of posture and load in 8 chronic spinal cord injured (SCI) and 10 spinal-intact subjects. The soleus H-reflex recruitment curve was established in all subjects while they were supine, seated, and standing on a stable treadmill. During standing, body weight support (BWS) was provided via an upper body harness and ranged in SCI subjects from 20%-50% and in spinal-intact subjects was set at 0% and 50%. Stimuli corresponding to the H-threshold (H(th)), maximal H-reflex amplitude (H(max)), and 50% of H(max) as well as the reflex gain were estimated based on a sigmoid function of the ascending limb of the soleus H-reflex recruitment curve. The soleus H-reflex gain, H(max) amplitude, and stimuli corresponding to H(th), 50% of H(max), and H(max) were increased in SCI subjects regardless of the body position and loading. Further, the reflex gain was not modulated appropriately during conditions of weight bearing in SCI subjects. Impaired spinal reflex excitability in SCI subjects is accompanied by changes of the H-reflex recruitment curve parameters regardless of presence or absence of body loading.

Flexion reflex modulation during stepping in human spinal cord injury.

The flexion reflex modulation pattern was investigated in nine people with a chronic spinal cord injury during stepping using body weight support on a treadmill and manual assistance by therapists. Body weight support was provided by an upper body harness and was adjusted for each subject to promote the best stepping pattern with the least manual assistance required by the therapists. The flexion reflex was elicited by sural nerve stimulation with a 30 ms pulse train at 1.2-2 times the tibialis anterior reflex threshold. During stepping, stimuli were randomly dispersed across the gait cycle which was divided into 16 equal bins. A long latency (>110 ms) flexion reflex was present in all subjects, while a short (>30 ms) and a medium latency (>70 ms) flexion reflex were present only in three subjects. For each response, the non-stimulated EMG was subtracted from the stimulated EMG at identical time windows and bins, normalized to the maximal corresponding EMG, and significant differences were established with a Wilcoxon rank-sum test. The long latency flexion reflex was facilitated at late stance and during the swing-to-stance transition phase. A reflex depression was present from heel strike until mid-stance and during the swing-to-stance transition phase. The short and medium latency flexion reflexes were depressed during mid-stance followed by facilitation during the stance-to-swing transition phase. Regardless of the latency, facilitatory flexion responses during the swing phase coincided with decreased activity of ipsilateral ankle extensors. The flexion reflex was modulated in a phase dependent manner, a behavior that was absent for the soleus H-reflex in most of these patients (Knikou et al. in Exp Brain Res 193:397-407, 2009). We propose that training should selectively target spinal reflex circuits in which extensor muscles and reflexes are involved in order to maximize sensorimotor recovery in these patients.

Soleus H-reflex modulation during body weight support treadmill walking in spinal cord intact and injured subjects.

The soleus H-reflex modulation pattern was investigated in ten spinal cord intact subjects during treadmill walking at varying levels of body weight support (BWS), and nine spinal cord injured (SCI) subjects at a BWS level that promoted the best stepping pattern. The soleus H-reflex was elicited by tibial nerve stimulation with a single 1-ms pulse at an intensity that the M-waves ranged from 4 to 8% of the maximal M-wave (M(max)). During treadmill walking, the H-reflex was elicited every four steps, and stimuli were randomly dispersed across the gait cycle which was divided into 16 equal bins. EMGs were recorded with surface electrodes from major left and right hip, knee, and ankle muscles. M-waves and H-reflexes at each bin were normalized to the M(max) elicited at 60-100 ms after the test reflex stimulus. For every subject, the integrated EMG area of each muscle was established and plotted as a function of the step cycle phase. The H-reflex gain was determined as the slope of the relationship between H-reflex and soleus EMG amplitudes at 60 ms before H-reflex elicitation for each bin. In spinal cord intact subjects, the phase-dependent H-reflex modulation, reflex gain, and EMG modulation pattern were constant across all BWS (0, 25, and 50) levels, while tibialis anterior muscle activity increased with less body loading. In three out of nine SCI subjects, a phase-dependent H-reflex modulation pattern was evident during treadmill walking at BWS that ranged from 35 to 60%. In the remaining SCI subjects, the most striking difference was an absent H-reflex depression during the swing phase. The reflex gain was similar for both subject groups, but the y-intercept was increased in SCI subjects. We conclude that the mechanisms underlying cyclic H-reflex modulation during walking are preserved in some individuals after SCI.

Feasibility of manual teach-and-replay and continuous impedance shaping for robotic locomotor training following spinal cord injury.

Robotic gait training is an emerging technique for retraining walking ability following spinal cord injury (SCI). A key challenge in this training is determining an appropriate stepping trajectory and level of assistance for each patient, since patients have a wide range of sizes and impairment levels. Here, we demonstrate how a lightweight yet powerful robot can record subject-specific, trainer-induced leg trajectories during manually assisted stepping, then immediately replay those trajectories. Replay of the subject-specific trajectories reduced the effort required by the trainer during manual assistance, yet still generated similar patterns of muscle activation for six subjects with a chronic SCI. We also demonstrate how the impedance of the robot can be adjusted on a step-by-step basis with an error-based, learning law. This impedance-shaping algorithm adapted the robot's impedance so that the robot assisted only in the regions of the step trajectory where the subject consistently exhibited errors. The result was that the subjects stepped with greater variability, while still maintaining a physiologic gait pattern. These results are further steps toward tailoring robotic gait training to the needs of individual patients.

Improvements in orthostatic instability with stand locomotor training in individuals with spinal cord injury.

Prospective assessment of cardiovascular control in individuals with spinal cord injury (SCI) in response to active stand training. Cardiovascular parameters were measured at rest and in response to orthostatic challenge before and after training in individuals with clinically complete SCI. The goal of this study was to evaluate the effect of active stand training on arterial blood pressure and heart rate and changes in response to orthostatic stress in individuals with SCI. Measurements were obtained in individuals with SCI (n=8) prior to and after 40 and 80 sessions of the standing component of a locomotor training intervention (stand LT). During standing, all participants wore a harness and were suspended by an overhead, pneumatic body weight support (BWS) system over a treadmill. Trainers provided manual facilitation as necessary at the trunk and legs. All individuals were able to bear more weight on their legs after the stand LT training. Resting arterial blood pressure significantly increased in individuals with cervical SCI after 80 training sessions. At the end of the training period, resting systolic blood pressure (BP) in individuals with cervical SCI in a seated position, increased by 24% (from 84 +/- 5 to 104 +/- 7 mmHg). Furthermore, orthostatic hypotension present in response to standing prior to training (decrease in systolic BP of 24 +/- 14 mmHg) was not evident (decrease in systolic BP of 0 +/- 11 mmHg) after 80 sessions of stand LT. Hemodynamic parameters of individuals with thoracic SCI were relatively stable prior to training and not significantly different after 80 sessions of stand LT. Improvements in resting arterial blood pressure and responses to orthostatic stress in individuals with clinically complete cervical SCI occurred following intensive stand LT training. These results may be attributed to repetitive neuromuscular activation of the legs from loading and/or conditioning of cardiovascular responses from repetitively assuming an upright posture.