Comprehensive assessment of walking function after human spinal cord injury

Improvement in Motor and Walking Capacity during Multisegmental Transcutaneous Spinal Stimulation in Individuals with Incomplete Spinal Cord Injury

Transcutaneous multisegmental spinal cord stimulation (tSCS) has shown superior efficacy in modulating spinal locomotor circuits compared to single-site stimulation in individuals with spinal cord injury (SCI). Building on these findings, we hypothesized that administering a single session of tSCS at multiple spinal segments may yield greater enhancements in muscle strength and gait function during stimulation compared to tSCS at only one or two segments. In our study, tSCS was applied at single segments (C5, L1, and Coc1), two segments (C5-L1, C5-Coc1, and L1-Coc1), or multisegments (C5-L1-Coc1) in a randomized order. We evaluated the 6-m walking test (6MWT) and maximum voluntary contraction (MVC) and assessed the Hmax/Mmax ratio during stimulation in ten individuals with incomplete motor SCI. Our findings indicate that multisegmental tSCS improved walking time and reduced spinal cord excitability, as measured by the Hmax/Mmax ratio, similar to some single or two-site tSCS interventions. However, only multisegmental tSCS resulted in increased tibialis anterior (TA) muscle strength. These results suggest that multisegmental tSCS holds promise for enhancing walking capacity, increasing muscle strength, and altering spinal cord excitability in individuals with incomplete SCI.

Assessing walking ability using a robotic gait trainer: opportunities and limitations of assist-as-needed control in spinal cord injury

BACKGROUND

Walking impairments are a common consequence of neurological disorders and are assessed with clinical scores that suffer from several limitations. Robot-assisted locomotor training is becoming an established clinical practice. Besides training, these devices could be used for assessing walking ability in a controlled environment. Here, we propose an adaptive assist-as-needed (AAN) control for a treadmill-based robotic exoskeleton, the Lokomat, that reduces the support of the device (body weight support and impedance of the robotic joints) based on the ability of the patient to follow a gait pattern displayed on screen. We hypothesize that the converged values of robotic support provide valid and reliable information about individuals' walking ability.

METHODS

Fifteen participants with spinal cord injury and twelve controls used the AAN software in the Lokomat twice within a week and were assessed using clinical scores (10MWT, TUG). We used a regression method to identify the robotic measure that could provide the most relevant information about walking ability and determined the test-retest reliability. We also checked whether this result could be extrapolated to non-ambulatory and to unimpaired subjects.

RESULTS

The AAN controller could be used in patients with different injury severity levels. A linear model based on one variable (robotic knee stiffness at terminal swing) could explain 74% of the variance in the 10MWT and 61% in the TUG in ambulatory patients and showed good relative reliability but poor absolute reliability. Adding the variable 'maximum hip flexor torque' to the model increased the explained variance above 85%. This did not extend to non-ambulatory nor to able-bodied individuals, where variables related to stance phase and to push-off phase seem more relevant.

CONCLUSIONS

The novel AAN software for the Lokomat can be used to quantify the support required by a patient while performing robotic gait training. The adaptive software might enable more challenging training conditions tuned to the ability of the individuals. While the current implementation is not ready for assessment in clinical practice, we could demonstrate that this approach is safe, and it could be integrated as assist-as-needed training, rather than as assessment.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02425332.

Feasibility of an Intelligent Algorithm Based on an Assist-as-Needed Controller for a Robot-Aided Gait Trainer (Lokomat) in Neurological Disorders: A Longitudinal Pilot Study

Most robotic gait assisted devices are designed to provide constant assistance during the training without taking into account each patient's functional ability. The Lokomat offers an assist-as-needed control via the integrated exercise "Adaptive Gait Support" (AGS), which adapts the robotic support based on the patient's abilities. The aims of this study were to examine the feasibility and characteristics of the AGS during long-term application. Ten patients suffering from neurological diseases underwent an 8-week Lokomat training with the AGS. They additionally performed conventional walking tests and a robotic force measurement. The difference between robotic support during adaptive and conventional training and the relationship between the robotic assessment and the conventional walking and force tests were examined. The results show that AGS is feasible during long-term application in a heterogeneous population. The support during AGS training in most of the gait phases was significantly lower than during conventional Lokomat training. A relationship between the robotic support level determined by the AGS and conventional walking tests was revealed. Moreover, combining the isometric force data and AGS data could divide patients into clusters, based on their ability to generate high forces and their level of motor control. AGS shows a high potential in assessing patients' walking ability, as well as in providing challenging training, e.g., by automatically adjusting the robotic support throughout the whole gait cycle and enabling training at lower robotic support.

Kinematic and Neuromuscular Adaptations in Incomplete Spinal Cord Injury after High- versus Low-Intensity Locomotor Training

Recent data demonstrate improved locomotion with high-intensity locomotor training (LT) in individuals with incomplete spinal cord injury (iSCI), although concerns remain regarding reinforcement of abnormal motor strategies. The present study evaluated the effects of LT intensity on kinematic and neuromuscular coordination in individuals with iSCI. Using a randomized, crossover design, participants with iSCI received up to 20 sessions of high-intensity LT, with attempts to achieve 70-85% of age-predicted maximum heart rate (HRmax), or low-intensity LT (50-65% HRmax), following which the other intervention was performed. Specific measures included spatiotemporal variables, sagittal-plane gait kinematics, and neuromuscular synergies from electromyographic (EMG) recordings. Correlation analyses were conducted to evaluate associations between variables. Significant improvements in sagittal-plane joint excursions and intralimb hip-knee coordination were observed following high- but not low-intensity LT when comparing peak treadmill (TM) speed before and after LT. Neuromuscular complexity (i.e., number of synergies to explain >90% of EMG variance) was also increased following high- but not low-intensity LT. Comparison of speed-matched trials confirmed significant improvements in the knee excursion of the less impaired limb and intralimb hip-knee coordination, as well as improvements in neuromuscular complexity following high-intensity LT. These findings suggest greater neuromuscular complexity may be due to LT and not necessarily differences in speeds. Only selected kinematic changes (i.e., weak hip excursion) was correlated to improvements in treadmill speed. In conclusion, LT intensity can facilitate gains in kinematic variables and neuromuscular synergies in individuals with iSCI.

Lower extremity outcome measures: considerations for clinical trials in spinal cord injury

STUDY DESIGN

This is a focused review article.

OBJECTIVES

To identify important concepts in lower extremity (LE) assessment with a focus on locomotor outcomes and provide guidance on how existing outcome measurement tools may be best used to assess experimental therapies in spinal cord injury (SCI). The emphasis lies on LE outcomes in individuals with complete and incomplete SCI in Phase II-III trials.

METHODS

This review includes a summary of topics discussed during a workshop focusing on LE function in SCI, conceptual discussion of corresponding outcome measures and additional focused literature review.

RESULTS

There are a number of sensitive, accurate, and responsive outcome tools measuring both quantitative and qualitative aspects of LE function. However, in trials with individuals with very acute injuries, a baseline assessment of the primary (or secondary) LE outcome measure is often not feasible.

CONCLUSION

There is no single outcome measure to assess all individuals with SCI that can be used to monitor changes in LE function regardless of severity and level of injury. Surrogate markers have to be used to assess LE function in individuals with severe SCI. However, it is generally agreed that a direct measurement of the performance for an appropriate functional activity supersedes any surrogate marker. LE assessments have to be refined so they can be used across all time points after SCI, regardless of the level or severity of spinal injury.

SPONSORS

Craig H. Neilsen Foundation, Spinal Cord Outcomes Partnership Endeavor.