Gait Control and Locomotor Recovery after Spinal Cord Injury

The gait of patients with an incomplete spinal cord injury (iSCI) has been studied previously. The most widely examined parameters to characterize iSCI gait are walking speed and time-distance measures (e.g., step length, step frequency, gait-cycle phases). In a clinical setting, the functional recovery of iSCI patients is routinely captured by specific outcome measures such as the 10-meter walk test (10mWT), the 6-minute walk test (6minWT) or the walking index for spinal cord injury (WISCI), which has been specifically established for this particular group of patients to score their walking ability. These measures are useful to monitor gross motor function and recovery during rehabilitation, but lack the ability to elucidate underlying mechanisms of gait alterations and recovery or subtle changes in locomotor pattern. In order to be able to appreciate the injury-induced deficits in locomotor control and to capture changes in motor function that may not be visible to the naked eye a sensitive and comprehensive tool is of need. The easiest way of assessing walking capacity is to collect data of walking speed and distance. Yet, one of the most obvious gait alterations in subjects with iSCI is an impaired gait quality. In the past, gait quality has been scored by trained investigators that rate defined features of walking. However, more complex movements that require precise spatial and temporal coordination of several joints and body segments are not easy to detect by mere observation. In the first study of this thesis, we evaluated the lower-limb coordination by means of combined hip-knee angular profiles (cyclograms). Patients showed distinct types and extents of cyclogram alterations and were thereupon categorized into four groups of impairment. The cyclogram seemed to reflect the underlying deficits as it correlated well with walking performance (speed) but could not be modulated with increasing speeds in contrast to a converging normalization in all control subjects. The intralimb coordination apparently is a sensitive indicator of motor-control impairment after spinal cord injury. We next evaluated a variety of gait-related parameters in order to find alterations of locomotor control after iSCI. With the aim of establishing a comprehensive framework to examine the organization of walking behavior in humans and how this organization gets distorted by insults to the spinal cord we chose a data-driven holistic approach for analyzing a multivariate set of data. This approach prevents a certain investigator-induced bias that arises when more or less arbitrarily pre-selecting a specific outcome measure. Multivariate in this case means variables of different modalities, i.e., objective electrophysiological measures that represent the integrity and electrical conductivity of specific spinal fiber tracts, kinematic measures that describe the extent of movements and body-segment coordination (i.e., gait quality) as well as measures that quantify locomotor performance such as walking speed and distance. Hence, clusters of parameters were identified that were or were not altered in iSCI patients and that were distinctly modulated with respect to speed. These findings suggest that there are distinguishable domains of neural control of walking that may be differently affected in specific neurological disorders. Consequently, the question arises as to which of these parameters change over time and what this might reveal about the mechanisms of recovery. These questions were addressed in the third study where the gait of iSCI patients was analyzed at several time points during rehabilitation in order to reveal those parameters that most strongly contribute to recovery, and also to reveal the responsiveness of the multimodal factors to an improvement in walking speed. Interestingly, the responsiveness of a single measure did not necessarily contribute to recovery, which is rather affected by the contribution of mutually interacting parameters. It remains to be elucidated where exactly the plastic changes leading to functional recovery take place and by what mechanisms they are mediated. The great challenge of spinal cord research is the cure for paralysis, or, in other words, a way to induce functional neural repair in the growth-inhibiting environment of the central nervous system (CNS). Even though it is known that spontaneous regeneration of severed neural tissue does virtually not occur in the CNS, recovery on a functional basis does happen. In the fourth study we demonstrated that the spinal cord is capable of extensive plastic changes induced by pathological processes in the absence of motor deficits and only minor sensory impairments. To accelerate the success of future clinical trials, the bridging from bench to bedside needs to be encouraged. Outcome measures should be standardized across species in order to appreciate differences and similarities. It could be shown that after a cervical hemisection of the spinal cord, equivalent to a the Brown-Séquard Syndrome in patients, humans and primates show superior recovery of function mediated by the corticospinal tract compared to rats. These findings support the importance of studies performed in primates to minimize the gap between preclinical and clinical outcome

Locomotor Recovery in Spinal Cord Injury: Insights Beyond Walking Speed and Distance

Recovery of locomotor function after incomplete spinal cord injury (iSCI) is clinically assessed through walking speed and distance, while improvements in these measures might not be in line with a normalization of gait quality and are, on their own, insensitive at revealing potential mechanisms underlying recovery. The objective of this study was to relate changes of gait parameters to the recovery of walking speed while distinguishing between parameters that rather reflect speed improvements from factors contributing to overall recovery. Kinematic data of 16 iSCI subjects were repeatedly recorded during in-patient rehabilitation. The responsiveness of gait parameters to walking speed was assessed by linear regression. Principal component analysis (PCA) was applied on the multivariate data across time to identify factors that contribute to recovery after iSCI. Parameters of gait cycle and movement dynamics were both responsive and closely related to the recovery of walking speed, which increased by 96%. Multivariate analysis revealed specific gait parameters (intralimb shape normality and consistency) that, although less related to speed increments, loaded highly on principal component one (PC1) (58.6%) explaining the highest proportion of variance (i.e., recovery of outcome over time). Interestingly, measures of hip, knee, and ankle range of motion showed varying degrees of responsiveness (from very high to very low) while not contributing to gait recovery as revealed by PCA. The conjunct application of two analysis methods distinguishes gait parameters that simply reflect increased walking speed from parameters that actually contribute to gait recovery in iSCI. This distinction may be of value for the evaluation of interventions for locomotor recovery

Preserved sensory-motor function despite large-scale morphological alterations in a series of patients with holocord syringomyelia

Although the central nervous system has a limited capacity for regeneration after acute brain and spinal cord injuries, it can reveal extensive morphological changes. Occasionally, the formation of an extensive syrinx in the spinal cord can be observed that causes no or only limited signs of functional impairment. This condition creates a unique opportunity to evaluate the mismatch between substantial morphological changes and functional outcomes. We identified seven patients with holocord syringomyelia affecting the cervical cord following chronic traumatic thoracic/lumbar spinal cord injury (19-34 years after injury) or holocord syringomyelia of non-traumatic origin, and anatomical syrinx dimensions (length, cross-sectional area) were determined using sagittal and axial magnetic resonance imaging scans. Motor- and sensory-pathway integrity were evaluated using electrophysiological assessments (i.e., motor, dermatomal sensory, and dermatomal contact-heat [dCHEP] evoked potentials, as well as nerve conduction studies). These were specifically compared to clinical measures of upper-limb strength and grasping performance, including three-dimensional motion analysis. Despite extensive anatomical changes of the cervical cord (on average 26% reduction of residual spinal cord area and intrusion of almost the entire cervical spinal cord), a clinically relevant impairment of upper-limb motor function was absent while only subtle sensory deficits could be detected. dCHEPs revealed the highest sensitivity by disclosing impairments of spinothalamic pathways. Comparable to that of the brain, extensive anatomical changes of the spinal cord can occur with only subtle functional impairment. The time scale of slowly-emerging morphological alterations is essential to permit an enormous capacity for plasticity of the spinal cord

Home-based virtual reality-augmented training improves lower limb muscle strength, balance, and functional mobility following chronic incomplete spinal cord injury

Key factors positively influencing rehabilitation and functional recovery after spinal cord injury (SCI) include training variety, intensive movement repetition, and motivating training tasks. Systems supporting these aspects may provide profound gains in rehabilitation, independent of the subject's treatment location. In the present study, we test the hypotheses that virtual reality (VR)-augmented training at home (i.e., unsupervised) is feasible with subjects with an incomplete SCI (iSCI) and that it improves motor functions such as lower limb muscle strength, balance, and functional mobility. In the study, 12 chronic iSCI subjects used a home-based, mobile version of a lower limb VR training system. The system included motivating training scenarios and combined action observation and execution. Virtual representations of the legs and feet were controlled via movement sensors. The subjects performed home-based training over 4 weeks, with 16-20 sessions of 30-45 min each. The outcome measures assessed were the Lower Extremity Motor Score (LEMS), Berg Balance Scale (BBS), Timed Up and Go (TUG), Spinal Cord Independence Measure mobility, Walking Index for Spinal Cord Injury II, and 10 m and 6 min walking tests. Two pre-treatment assessment time points were chosen for outcome stability: 4 weeks before treatment and immediately before treatment. At post-assessment (i.e., immediately after treatment), high motivation and positive changes were reported by the subjects (adapted Patients' Global Impression of Change). Significant improvements were shown in lower limb muscle strength (LEMS, P = 0.008), balance (BBS, P = 0.008), and functional mobility (TUG, P = 0.007). At follow-up assessment (i.e., 2-3 months after treatment), functional mobility (TUG) remained significantly improved (P = 0.005) in contrast to the other outcome measures. In summary, unsupervised exercises at home with the VR training system led to beneficial functional training effects in subjects with chronic iSCI, suggesting that it may be useful as a neurorehabilitation tool. Trial registration: Canton of Zurich ethics committee (EK-24/2009, PB_2016-00545), ClinicalTrials.gov: NCT02149186. Registered 24 April 2014

Influence of spinal cord integrity on gait control in human spinal cord injury

BACKGROUND Clinical trials in spinal cord injury (SCI) primarily rely on simplified outcome metrics (ie, speed, distance) to obtain a global surrogate for the complex alterations of gait control. However, these assessments lack sufficient sensitivity to identify specific patterns of underlying impairment and to target more specific treatment interventions. OBJECTIVE To disentangle the differential control of gait patterns following SCI beyond measures of time and distance. METHODS The gait of 22 individuals with motor-incomplete SCI and 21 healthy controls was assessed using a high-resolution 3-dimensional motion tracking system and complemented by clinical and electrophysiological evaluations applying unbiased multivariate analysis. RESULTS Motor-incomplete SCI patients showed varying degrees of spinal cord integrity (spinal conductivity) with severe limitations in walking speed and altered gait patterns. Principal component (PC) analysis applied on all the collected data uncovered robust coherence between parameters related to walking speed, distortion of intralimb coordination, and spinal cord integrity, explaining 45% of outcome variance (PC 1). Distinct from the first PC, the modulation of gait-cycle variables (step length, gait-cycle phases, cadence; PC 2) remained normal with respect to regained walking speed, whereas hip and knee ranges of motion were distinctly altered with respect to walking speed (PC 3). CONCLUSIONS In motor-incomplete SCI, distinct clusters of discretely controlled gait parameters can be discerned that refine the evaluation of gait impairment beyond outcomes of walking speed and distance. These findings are specifically different from that in other neurological disorders (stroke, Parkinson) and are more discrete at targeting and disentangling the complex effects of interventions to improve walking outcome following motor-incomplete SCI

Exploring lumbo-pelvic functional behaviour patterns during osteopathic motion tests ::a biomechanical (en)active inference approach to movement analysis

Background: Observing how individuals actively adapt to their environment may provide additional insights into traditional clinical tests. Rather than using tests that only identify joint mobility limitations, it seems relevant to use clinical motion tests that assess global biomechanical functions more generally and identify functional behaviours. Objectives: This study explores whether different functional kinematic behaviour patterns appear when executing a new complex motor task and whether those observations are consistent over multiple executions. Methods: Marker-based kinematic analyses of the lumbo-pelvic complex were conducted on 29 asymptomatic athletes during two active self-induced motion tests: the one-sided tilt test and a modified version of this test limiting the trunk axial rotation. Marker data served as an input for a full musculoskeletal model to compute the lumbar and lower limb joint angles. Latent class analysis and intraclass correlation coefficients were calculated to identify different classes of functional kinematic behaviour and assess the reliability between measurements. Results: The methodology allowed us to identify four distinctive classes of possible movement combinations based on these two functional tests: standard movement, low knee and lumbar engagement, high pelvis engagement and high lumbar flexion. All ICCs for the lumbo-pelvic complex degrees of freedom were higher than 0.6, suggesting a moderate to good reliability for the overall test. Conclusion: It remains unknown whether the observed reproducible patterns emerging from the motion test relate to motivation and prior experiences. Further exploration is required to investigate whether these behaviours can be correlated to empirical clinical observations, past experiences, and future vulnerabilities for musculoskeletal condition

Overground walking patterns after chronic incomplete spinal cord injury show distinct response patterns to unloading

Abstract Background Body weight support (BWS) is often provided to incomplete spinal cord injury (iSCI) patients during rehabilitation to enable gait training before full weight-bearing is recovered. Emerging robotic devices enable BWS during overground walking, increasing task-specificity of the locomotor training. However, in contrast to a treadmill setting, there is little information on how unloading is integrated into overground locomotion. We investigated the effect of a transparent multi-directional BWS system on overground walking patterns at different levels of unloading in individuals with chronic iSCI (CiSCI) compared to controls. Methods Kinematics of 12 CiSCI were analyzed at six different BWS levels from 0 to 50% body weight unloading during overground walking at 2kmh− 1 and compared to speed-matched controls. Results In controls, temporal parameters, single joint trajectories, and intralimb coordination responded proportionally to the level of unloading, while spatial parameters remained unaffected. In CiSCI, unloading induced similar changes in temporal parameters. CiSCI, however, did not adapt their intralimb coordination or single joint trajectories to the level of unloading. Conclusions The findings revealed that continuous, dynamic unloading during overground walking results in subtle and proportional gait adjustments corresponding to changes in body load. CiSCI demonstrated diminished responses in specific domains of gait, indicating that their altered neural processing impeded the adjustment to environmental constraints. CiSCI retain their movement patterns under overground unloading, indicating that this is a viable locomotor therapy tool that may also offer a potential window on the diminished neural control of intralimb coordination

Functional assessment of the stomatognathic system. Part 1: The role of static elements of analysis

To review the elements of static analysis in the functional assessment of the stomatognathic system, as promoted for more than a century by gnathologists, and summarize the available scientific evidence, including anthropologic observations. A thorough search was conducted using PubMed, the Cochrane Library database, and Google Scholar. From peer-reviewed articles and other scientific literature, up-to-date information addressing three topics was identified: (a) the anthropologic perspective with particular consideration for the role of progressive dental wear over time, (b) descriptions of gnathologic principles and evidence on their scientific validity, and (c) the methodologic inaccuracies introduced by seeking to correlate variables directly rather than allowing for causal inference. For decades gnathology attempted to describe a structure-function correlation within the stomatognathic system by means of a model whose principles were static and mechanistic references. No scientific validation was ever achieved, placing clinical and research consensus out of reach. A historical perspective helps to place the fundamentals of gnathology into context: They were conceived to solve technical difficulties but were then assumed to be physiologic stereotypes. This misconception led to a decades-long promotion of mechanistic theories to describe oral function, but the evidence available today supports a more flexible and adaptable approach. Gnathologic arguments have been relegated to become exclusively of technical relevance in oral rehabilitation.</p