Evaluation of the lower motor neuron integrity of upper extremity muscles in high level spinal cord injury

Neuromuscular consequences of spinal cord injury: New mechanistic insights and clinical considerations

The spinal cord facilitates communication between the brain and the body, containing intrinsic systems that work with lower motor neurons (LMNs) to manage movement. Spinal cord injuries (SCIs) can lead to partial paralysis and dysfunctions in muscles below the injury. While traditionally this paralysis has been attributed to disruptions in the corticospinal tract, a growing body of work demonstrates LMN damage is a factor. Motor units, comprising the LMN and the muscle fibers with which they connect, are essential for voluntary movement. Our understanding of their changes post-SCI is still emerging, but the health of motor units is vital, especially when considering innovative SCI treatments like nerve transfer surgery. This review seeks to collate current literature on how SCI impact motor units and explore neuromuscular clinical implications and treatment avenues. SCI reduced motor unit number estimates, and surviving motor units had impaired signal transmission at the neuromuscular junction, force-generating capacity, and excitability, which have the potential to recover chronically, yet the underlaying mechanisms are unclear. Furthermore, electrodiagnostic evaluations can aid in assessing the health lower and upper motor neurons, identify suitable targets for nerve transfer surgeries, and detect patients with time sensitive injuries. Lastly, many electrodiagnostic abnormalities occur in both chronic and acute SCI, yet factors contributing to these abnormalities are unknown. Future studies are required to determine how motor units adapt following SCI and the clinical implications of these adaptations.

Hybrid FES-exoskeleton control: Using MPC to distribute actuation for elbow and wrist movements

Introduction

Individuals who have suffered a cervical spinal cord injury prioritize the recovery of upper limb function for completing activities of daily living. Hybrid FES-exoskeleton systems have the potential to assist this population by providing a portable, powered, and wearable device; however, realization of this combination of technologies has been challenging. In particular, it has been difficult to show generalizability across motions, and to define optimal distribution of actuation, given the complex nature of the combined dynamic system.

Methods

In this paper, we present a hybrid controller using a model predictive control (MPC) formulation that combines the actuation of both an exoskeleton and an FES system. The MPC cost function is designed to distribute actuation on a single degree of freedom to favor FES control effort, reducing exoskeleton power consumption, while ensuring smooth movements along different trajectories. Our controller was tested with nine able-bodied participants using FES surface stimulation paired with an upper limb powered exoskeleton. The hybrid controller was compared to an exoskeleton alone controller, and we measured trajectory error and torque while moving the participant through two elbow flexion/extension trajectories, and separately through two wrist flexion/extension trajectories.

Results

The MPC-based hybrid controller showed a reduction in sum of squared torques by an average of 48.7 and 57.9% on the elbow flexion/extension and wrist flexion/extension joints respectively, with only small differences in tracking accuracy compared to the exoskeleton alone.

Discussion

To realize practical implementation of hybrid FES-exoskeleton systems, the control strategy requires translation to multi-DOF movements, achieving more consistent improvement across participants, and balancing control to more fully leverage the muscles' capabilities.

Split-elbow sign in the PRO-ACT and Southern Italy ALS cohorts: a potential marker of disease severity and lower motor neuron involvement?

INTRODUCTION

Split phenomena in ALS refers to the preferential dysfunction of some groups of muscles over others. The split-elbow sign (SE) is characterized by the predominant weakness of the biceps compared to the triceps, but available results are conflicting.

OBJECTIVES

To evaluate the prevalence of the SE in two independent cohorts: the randomized controlled trial-based PRO-ACT cohort (n = 500) and a monocentric cohort of patients with ALS from Southern Italy (n = 144); to investigate the demographic and clinical variables associated with the SE sign.

METHODS

Wilcoxon signed-rank test was used to compare biceps with triceps power in the same limb measured by hand-held dynamometry in the PRO-ACT cohort and Medical Research Council (MRC) in our cohort. Each limb was considered independently and not paired within the same individual. The arm where the triceps was stronger than the biceps was defined SE + , whereas the arm where the biceps was stronger than the triceps was considered SE-. A backward stepwise multivariate logistic regression was used to analyze the relationship between clinical and demographic variables and SE. PENN Upper Motor Neuron and Devine scales were used to evaluate the different upper (UMN) and lower (LMN) motor neuron impairments between the SE + and SE- arms.

RESULTS

In both cohorts, the biceps were on average stronger than the triceps, and the SE sign was present in 41% of the PRO-ACT cohort and just 30% of the Southern Italy cohort. The multivariate logistic regression revealed that older age (OR: 1.45; p = 0.01), male gender (OR: 1.55; p = 0.002), spinal onset (OR: 1.59; p = 0.007), and higher disease severity (OR: 1.70; p = 0.001) were significant predictors of the SE sign in the PRO-ACT cohort. Conversely, in Southern Italy patients, only a lower ALSFRS-R score was a significant determinant of the SE (OR: 8.47; p = 0.008). Finally, SE + arms exhibited a significantly higher median Devine sub-score compared to SE- [1 vs 0, p = < 0.05], while arms SE- showed a significantly higher median PUMNS sub-score [2 vs 0; p = < 0.05)].

CONCLUSION

In our study, most patients with ALS do not show SE. Patients with SE are more likely older, males, with spinal onset, a higher degree of disease severity, and predominant and wider LMN impairment.

Lower motoneuron dysfunction impacts spontaneous motor recovery in acute cervical spinal cord injury

Paresis after spinal cord injury is caused by damage to upper and lower motoneurons and may differentially impact neurological recovery. This prospective monocentric longitudinal observational study investigated the extent and severity of lower motoneuron dysfunction and its impact on upper extremity motor recovery after acute cervical spinal cord injury. Pathological spontaneous activity at rest and/or increased discharge rates of motor unit action potentials recorded by needle electromyography (EMG) were taken as parameters for lower motoneuron dysfunction and its relation to the extent of myelopathy in the first available spine MRI was determined. Motor recovery was assessed by standardized neurological examination within the first 4 weeks (acute stage) and up to 1 year (chronic stage) after injury. Eighty-five muscles of 17 individuals with cervical spinal cord injury (neurological level of injury from C1 to C7) and a median age of 54 (28-59) were examined. The results showed that muscles with signs of lower motoneuron dysfunction peaked at the lesion center (Χ²[2,n=85]=6.6, p=0.04) and that the severity of lower motoneuron dysfunction correlated with T2-weighted hyperintense MRI signal changes in routine spine MRI at the lesion site (spearman ρ=0.31, p=0.01). Muscles exhibiting signs of lower motoneuron dysfunction, as indicated by pathological spontaneous activity at rest and/or increased discharge rates of motor unit action potentials, were associated with more severe paresis in both the acute and chronic stages after spinal cord injury (spearman ρ acute=-0.22, p=0.04 and chronic=-0.31, p=0.004). Moreover, the severity of lower motoneuron dysfunction in the acute stage was also associated with a greater degree of paresis (spearman ρ acute=-0.24, p=0.03 and chronic=-0.35, p=0.001). While both muscles with and without signs of lower motoneuron dysfunction were capable of regaining strength over time, those without lower motoneuron dysfunctions had a higher potential to reach full strength. Muscles with signs of lower motoneuron dysfunction in the acute stage displayed increased amplitudes of motor unit action potentials with chronic-stage needle EMG, indicating reinnervation through peripheral collateral sprouting as compensatory mechanism (Χ²[1,n=72]=4.3, p=0.04). Thus, lower motoneuron dysfunction represents a relevant factor contributing to motor impairment and recovery in acute cervical spinal cord injury. Defined recovery mechanisms (peripheral reinnervation) may at least partially underlie spontaneous recovery in respective muscles. Therefore, assessment of lower motoneuron dysfunction could help refine prediction of motor recovery following spinal cord injury.

A Therapeutic Strategy for Lower Motor Neuron Disease and Injury Integrating Neural Stem Cell Transplantation and Functional Electrical Stimulation in a Rat Model

Promising treatments for upper motor neuron disease are emerging in which motor function is restored by brain–computer interfaces and functional electrical stimulation. At present, such technologies and procedures are not applicable to lower motor neuron disease. We propose a novel therapeutic strategy for lower motor neuron disease and injury integrating neural stem cell transplantation with our new functional electrical stimulation control system. In a rat sciatic nerve transection model, we transplanted embryonic spinal neural stem cells into the distal stump of the peripheral nerve to reinnervate denervated muscle, and subsequently demonstrated that highly responsive limb movement similar to that of a healthy limb could be attained with a wirelessly powered two-channel neurostimulator that we developed. This unique technology, which can reinnervate and precisely move previously denervated muscles that were unresponsive to electrical stimulation, contributes to improving the condition of patients suffering from intractable diseases of paralysis and traumatic injury.

Shared Control of Elbow Movements with Functional Electrical Stimulation and Exoskeleton Assistance

Individuals who suffer from paralysis as a result of a spinal cord injury list restoration of arm and hand function as a top priority. FES helps restore movement using the user's own muscles, but does not produce accurate and repeatable movements necessary for many functional tasks. Robots can assist users in achieving accurate and repeatable movements, but often require bulky hardware to generate the necessary torques. We propose sharing torque requirements between a robot and FES to reduce robot torque output compared to a robot acting alone, yet maintain high accuracy. Cooperative PD and model predictive control algorithms were designed to share the control between these two torque sources. Corresponding PD and MPC algorithms that do not use FES were also designed. The control algorithms were tested with 10 able-bodied subjects. Torque and position tracking accuracy were compared when the system was commanded to follow a functional elbow flexion/extension trajectory. The robot torque required to achieve these movements was reduced for the shared control cases compared to the algorithms acting without FES. We observed a reduction in position accuracy with the MPC shared controller compared to the PD shared controller, while the MPC shared controller resulted in greater reductions in torque requirements. Both of these shared algorithms showed improvements over existing options, and can be used on any given trajectory, allowing for better transferability to functional tasks.

Soft robotics and functional electrical stimulation advances for restoring hand function in people with SCI: a narrative review, clinical guidelines and future directions

Background

Recovery of hand function is crucial for the independence of people with spinal cord injury (SCI). Wearable devices based on soft robotics (SR) or functional electrical stimulation (FES) have been employed to assist the recovery of hand function both during activities of daily living (ADLs) and during therapy. However, the implementation of these wearable devices has not been compiled in a review focusing on the functional outcomes they can activate/elicit/stimulate/potentiate. This narrative review aims at providing a guide both for engineers to help in the development of new technologies and for clinicians to serve as clinical guidelines based on the available technology in order to assist and/or recover hand function in people with SCI.

Methods

A literature search was performed in Scopus, Pubmed and IEEE Xplore for articles involving SR devices or FES systems designed for hand therapy or assistance, published since 2010. Only studies that reported functional outcomes from individuals with SCI were selected. The final collections of both groups (SR and FES) were analysed based on the technical aspects and reported functional outcomes.

Results

A total of 37 out of 1101 articles were selected, 12 regarding SR and 25 involving FES devices. Most studies were limited to research prototypes, designed either for assistance or therapy. From an engineering perspective, technological improvements for home-based use such as portability, donning/doffing and the time spent with calibration were identified. From the clinician point of view, the most suitable technical features (e.g., user intent detection) and assessment tools should be determined according to the particular patient condition. A wide range of functional assessment tests were adopted, moreover, most studies used non-standardized tests.

Conclusion

SR and FES wearable devices are promising technologies to support hand function recovery in subjects with SCI. Technical improvements in aspects such as the user intent detection, portability or calibration as well as consistent assessment of functional outcomes were the main identified limitations. These limitations seem to be be preventing the translation into clinical practice of these technological devices created in the laboratory.

Rehabilitation of Upper Limb Motor Impairment in Stroke: A Narrative Review on the Prevalence, Risk Factors, and Economic Statistics of Stroke and State of the Art Therapies

Stroke has been one of the leading causes of disability worldwide and is still a social health issue. Keeping in view the importance of physical rehabilitation of stroke patients, an analytical review has been compiled in which different therapies have been reviewed for their effectiveness, such as functional electric stimulation (FES), noninvasive brain stimulation (NIBS) including transcranial direct current stimulation (t-DCS) and transcranial magnetic stimulation (t-MS), invasive epidural cortical stimulation, virtual reality (VR) rehabilitation, task-oriented therapy, robot-assisted training, tele rehabilitation, and cerebral plasticity for the rehabilitation of upper extremity motor impairment. New therapeutic rehabilitation techniques are also being investigated, such as VR. This literature review mainly focuses on the randomized controlled studies, reviews, and statistical meta-analyses associated with motor rehabilitation after stroke. Moreover, with the increasing prevalence rate and the adverse socio-economic consequences of stroke, a statistical analysis covering its economic factors such as treatment, medication and post-stroke care services, and risk factors (modifiable and non-modifiable) have also been discussed. This review suggests that if the prevalence rate of the disease remains persistent, a considerable increase in the stroke population is expected by 2025, causing a substantial economic burden on society, as the survival rate of stroke is high compared to other diseases. Compared to all the other therapies, VR has now emerged as the modern approach towards rehabilitation motor activity of impaired limbs. A range of randomized controlled studies and experimental trials were reviewed to analyse the effectiveness of VR as a rehabilitative treatment with considerable satisfactory results. However, more clinical controlled trials are required to establish a strong evidence base for VR to be widely accepted as a preferred rehabilitation therapy for stroke.

Can Magnetic Resonance Imaging Reveal Lower Motor Neuron Damage after Traumatic Spinal Cord Injury? A Scoping Review

Restoring muscle function to patients with spinal cord injuries (SCIs) will invariably require a functioning lower motor neuron (LMN). As techniques such as nerve transfer surgery emerge, characterizing the extent of LMN damage associated with SCIs becomes clinically important. Current methods of LMN diagnosis have inherent limitations that could potentially be overcome by the development of magnetic resonance imaging (MRI) biomarkers: specific features on MRI that are indicative of LMN integrity. To identify research on MRI biomarkers of LMN damage in the acute phase after SCI, we searched PubMed, EMBASE, MEDLINE, and the Cochrane Central Register of Controlled Trials for articles published from inception to April 27, 2021. Overall, 2 of 58 unique articles screened met our inclusion criteria, both of which were small studies. We therefore identify MRI biomarkers of LMN damage overlying SCI as a notable gap in the literature. Because of the lack of existing literature on this specific problem, we further our discussion by examining concepts explored in research characterizing MRI biomarkers of spinal cord and neuronal damage in different contexts that may provide value in future work to identify a biomarker for LMN damage in SCI. We conclude that MRI biomarkers of LMN damage in SCI is an underexplored, but promising, area of research as emerging, function-restoring therapies requiring this information continue to advance.

Assessment of the upper limb of the tetraplegic patient

The aim of our study is to describe the assessment of the upper limb in tetraplegic patients to follow his (her) neurological progression and to define the medical or surgical treatment program. We selected upper limb assessment tools and scales for tetraplegic patients described in the medical literature through a PubMed search over the last four decades. For each method, we present the implementation rules and its metrological properties, including its validity in French. We selected five clinical scales for functional evaluation of grasping, as well as four scales for evaluating the overall function of these patients. Finally, we identified three complementary precision assessment tools. The AIS (ASIA Impairment Scale) classification describes the level and the severity of the spinal cord lesion. The Giens classification is more practical for describing the upper limb in middle and low tetraplegia. Impairments can be assessed with most common generic scales and nonspecific measurement devices: range of motion, strength, sensory loss, spasticity, joint pain. Measurement of pinch and grip strength is widely used and easy to perform. The Capabilities of Upper Extremity (CUE) and the Jebsen Taylor Test are the best validated and usable scales. At a general functional level, the Spinal Cord Independence Measure (SCIM) is the most relevant scale in these patients. Motor nerve blocks, electromyography, movement analysis and echography are promising additional methods. Assessment of the upper limb of tetraplegic patients relies both on generic and specific assessment tools and scales.

Lower Motor Neuron Abnormality in Chronic Cervical Spinal Cord Injury: Implications for Nerve Transfer Surgery

Nerve transfer surgery (NT) constitutes an exciting option to improve upper limb functions in chronic spinal cord injury (SCI), but requires intact sublesional lower motor neuron (LMN) health. The purpose of this study was to characterize patterns of LMN abnormality in nerve-muscle groups that are the potential recipients of NT, using a standardized electrodiagnostic examination, in individuals with chronic SCI (injury duration >2 years, injury levels C4-T1). The LMN abnormality was determined using a semihierarchical approach, combining the amplitude compound muscle action potential (CMAP) and abnormal spontaneous activity on needle electromyography (EMG). Ten participants (46 potential recipient muscles) were included (median age, 42.5 years; six males and four females; median duration from injury, 15.5 years). A high frequency of LMN abnormality was observed (87%), although there was substantial variation within and between individuals. No statistically significant discordance was observed between LMN abnormality on CMAP and EMG (p = 0.24), however, 50% of muscles with normal CMAP demonstrated abnormal spontaneous activity. The high frequency of LMN abnormality in recipient nerve-muscle groups has implications to candidate selection for NT surgery in chronic SCI and supports the important role of the pre-operative electrodiagnostic examination. Our results further support the inclusion of both CMAP and needle EMG parameters for characterization of LMN health. Although the number of nerve-muscle groups with normal LMN health was small (13%), this underscores the neurophysiological potential of some patients with chronic injuries to benefit from NT surgery.

Rehabilitation of Spinal Cord Injury: WFNS Spine Committee Recommendations

Spinal cord injury (SCI) is accompanied by a significant number of complications associated with damage to the spinal cord, gross functional impairments leading to limited self-care and movement, leading to a high level of disability, social and psychological maladaptation of the patients. Besides, pain and spasticity negatively affect rehabilitation programs. This search was conducted in PubMed/MEDLINE database. All studies published in English language (n = 16,297) were considered for inclusion. Of all studies evaluating rehabilitation in SCI patients (n = 80) were included. Based on the literature review the faculty of the WFNS Spine Committee created statements covering different aspects of the contemporary rehabilitation process of the SCI patients. The prepared statements were subjected to discussions, followed by anonymous voting process by the members of the WFNS Spine Committee. As result of the diccussions and the voting process the statements were modified and published as recommendations of the WFNS Spine Committee. The care for the SCI has gone a long way from the times after the World War II when these patients were considered hopeless in terms of any functional recovery, to the contemporary comprehensive rehabilitation programs. The rehabilitation is important part of the modern comprehencive treatment of SCI patients nowadays. The current manuscript reflects different aspects of the contemporary rehabilitaton process and decision makings, which were discussed by the faculty of the WFNS Spine Committee resulting in issuing of the following recommendations.

Predicting functional force production capabilities of upper extremity functional electrical stimulation neuroprostheses: a proof of concept study

OBJECTIVE

This study's goal was to demonstrate person-specific predictions of the force production capabilities of a paralyzed arm when actuated with a functional electrical stimulation (FES) neuroprosthesis. These predictions allow us to determine, for each hand position in a person's workspace, if FES activated muscles can produce enough force to hold the arm against gravity and other passive forces, the amount of force the arm can potentially exert on external objects, and in which directions FES can move the arm.

APPROACH

We computed force production predictions for a person with high tetraplegia and an FES neuroprosthesis used to activate muscles in her shoulder and arm. We developed Gaussian process regression models of the force produced at the end of the forearm when stimulating individual muscles at different wrist positions in the person's workspace. For any given wrist position, we predicted all possible forces a person can produce by any combination of individual muscles. Based on the force predictions, we determined if FES could produce force sufficient to overcome passive forces to hold a wrist position, the maximum force FES could produce in all directions, and the set of directions in which FES could move the arm. To estimate the error in our predictions, we then compared our force predictions based on single-muscle models to the actual forces produced when stimulating combinations of the person's muscles.

MAIN RESULTS

Our models classified the person's ability to hold static arm positions correctly for 83% (Session #1) and 69% (Session #2) for 39 wrist positions over two sessions. We predicted this person's ability to produce force at the end of her arm with an RMS error of 5.5 N and the percent of directions for which FES could achieve motion with RMS error of 10%. The accuracy of these predictions is similar to that found in the literature for FES systems with fewer degrees of freedom and fewer muscles.

SIGNIFICANCE

These person and device-specific predictions of functional capabilities of the arm allow neuroprosthesis developers to set achievable functional objectives for the systems they develop. These predictions can potentially serve as a screening tool for clinicians to use in planning neuroprosthetic interventions, greatly reducing the risk and uncertainty in such interventions.

Evaluation for Late Nerve Transfer Surgery in Spinal Cord Injury: Predicting the Degree of Lower Motor Neuron Injury

PURPOSE

Nerve transfer surgery is used to restore upper extremity function following cervical spinal cord injury (SCI) with substantial variation in outcomes. The injury pattern in SCI is complex and can include isolated upper motor neuron (UMN) and combined UMN/lower motor neuron (LMN) dysfunction. The purpose of the study was to determine the most effective diagnostic technique for determining suitable candidates for nerve transfer surgery in SCI.

METHODS

Medical records were reviewed of patients who had nerve transfers to restore upper extremity function in SCI. Data collected included (1) preoperative clinical examination and electrodiagnostic testing; (2) intraoperative neuromuscular stimulation (NMS); and (3) nerve histopathology. Preoperative, intraoperative, and postoperative data were compared to identify predictors of isolated UMN versus combined UMN/LMN injury patterns.

RESULTS

The study sample included 22 patients with 50 nerve transfer surgeries and included patients ranging from less than 1 year to over a decade post-SCI. Normal recipient nerve conduction studies (NCS) before surgery corresponded to the intraoperative presence of recipient NMS and postoperative histopathology that showed normal nerve architecture. Conversely, abnormal recipient NCS before surgery corresponded with the absence of recipient NMS during surgery and patterns of denervation on postoperative histopathology. Normal donor preoperative manual muscle testing corresponded with the presence of donor NMS during surgery and normal nerve architecture on postoperative histopathology. An EMG of corresponding musculature did not correspond with intraoperative donor or recipient NMS or histopathological findings.

CONCLUSIONS

NCS better predict patterns of injury in SCI than EMG. This is important information for clinicians evaluating people for late nerve transfer surgery even years post-SCI.

TYPE OF STUDY/LEVEL OF EVIDENCE

Diagnostic II.

Strength-Duration Curves of Radial Nerve in Patients With Lateral Elbow Pain

CONTEXT

Lateral epicondylalgia (LE) refers to a painful condition at or around the lateral epicondyle of the humerus. LE is one of the most common injuries of the elbow; however, the cause of the pathology is not clear. Patients often experience symptoms consistent with a radial nerve injury; however, data on the involvement of the radial nerve are needed.

OBJECTIVE

To analyze the relationship between electrophysiologic excitability and morphology of the radial nerve in patients with unilateral chronic LE.

DESIGN

Cross-sectional study.

SETTING

Department of Physiotherapy, University of Seville.

PATIENTS

A total of 56 elbows (28 right, 28 left) in 28 patients (12 females, 16 males; age 49 [7.37] y) were recruited by convenience sampling.

MAIN OUTCOME MEASURES

Strength-duration curves (chronaxia and accommodation index) and cross-sectional area (CSA) of the radial nerve were made in all participants. All parameters were compared between both limbs. Also, pain with palpation in the lateral epicondyle and functional pain of involved extremities was assessed using visual analog scale and the Patient-Rated Tennis Elbow Evaluation, respectively.

RESULTS

Symptomatic limb showed higher CSA values of the radial nerve when compared with the asymptomatic limb (P < .001). On the symptomatic limb, duration of symptoms was positively correlated with CSA values. Chronaxia values were all normal and similar between both limbs (P = .35). Regarding accommodation index, 14 (54%) patients showed accommodation indices that suggested pathological radial nerve on the right limb, 4 (14%) on the left limb, 5 (18%) on both limbs, and 4 (14%) had none of the affected nerves. Eight-six percent of patients showed accommodation indices that suggested pathological radial nerve, independently of symptomatic limb. In these cases, affected nerves had higher CSA than the unaffected nerve (P = .01). On the affected nerves, duration of symptoms was positively correlated with accommodation indices.

CONCLUSIONS

These findings suggest that patients with unilateral chronic LE show a decreased excitability in any radial nerve, independently of the symptomatic limb, and that pathological nerves have higher CSA than the nonpathological nerves.

Advanced Assessment of the Upper Limb in Tetraplegia: A Three-Tiered Approach to Characterizing Paralysis

Background: More than half of all individuals who sustain a spinal cord injury (SCI) experience some degree of impairment in the upper limb. Functional use of the arm and hand is of paramount importance to these individuals. Fortunately, the number of clinical trials and advanced interventions targeting upper limb function are increasing, generating optimism for improved recovery and restoration after SCI. New interventions for restoring function and improving recovery require more detailed examination of the motor capacities of the upper limb. Objectives: The purpose of this article is to introduce a three-tiered approach to evaluating motor function, with specific attention to the characteristics of weak and fully paralyzed muscles during acute rehabilitation. The three tiers include (1) evaluation of voluntary strength via manual muscle testing, (2) evaluation of lower motor neuron integrity in upper motor neuron-paralyzed muscles using surface electrical stimulation, and (3) evaluation of latent motor responses in paralyzed muscles that exhibit a strong response to electrical stimulation, using surface electromyographic recording electrodes. These characteristics contribute important information that can be utilized to mitigate potential secondary conditions such as contractures and identify effective interventions such as activity-based interventions or reconstructive procedures. Our goal is to encourage frontline clinicians - occupational and physical therapists who are experts in muscle assessment - to consider a more in-depth analysis of paralysis after SCI. Conclusion: Given the rapid advancements in SCI research and clinical interventions, it is critical that methods of evaluation and classification evolve. The success or failure of these interventions may depend on the specific characteristics identified in our three-tiered assessment. Without this assessment, the physiological starting point for each individual is unknown, adding significant variability in the outcomes of these interventions.

The Use of Nerve Transfers to Restore Upper Extremity Function in Cervical Spinal Cord Injury

BACKGROUND

Nerve transfer surgery to restore upper extremity function in cervical spinal cord injury (SCI) is novel and may transform treatment. Determining candidacy even years post-SCI is ill defined and deserves investigation.

OBJECTIVE

To develop a diagnostic algorithm, focusing on electrodiagnostic (EDX) studies, to determine eligibility for nerve transfer surgery.

DESIGN

Retrospective descriptive case series.

SETTING

Tertiary university-based institution.

PATIENTS

Individuals with cervical SCI (n = 45).

METHODS

The electronic medical records of people referred to the Plastic Surgery Multidisciplinary Upper Extremity Surgery in SCI clinic from 2010-2015 were reviewed. People were considered for nerve transfers to restore elbow extension or finger flexion and/or extension. Data including demographic, clinical evaluation, EDX results, surgery, and outcomes were collected and analyzed.

MAIN OUTCOME MEASUREMENTS

EDX data, including nerve conduction studies and electromyography, for bilateral upper extremities of each patient examined was used to assess for the presence of lower motor neuron injury, which would preclude late nerve transfer.

RESULTS

Based on our criteria and the results of EDX testing, a substantial number of patients presenting even years post-SCI were candidates for nerve transfers. Clinical outcome results are heterogeneous but promising and suggest that further refinement of eligibility, long-term follow-up, and standardized assessment will improve our understanding of the role of nerve transfer surgery to restore function in people with midcervical SCI.

CONCLUSIONS

Many patients living with SCI are candidates for nerve transfer surgery to restore upper extremity function. Although the ultimate efficacy of these surgeries is not yet determined, this study attempts to report the criteria we are using and may ultimately determine the timing for intervention and which transfers are most useful for this heterogeneous population.

LEVEL OF EVIDENCE

IV.

Considerations and recommendations for selection and utilization of upper extremity clinical outcome assessments in human spinal cord injury trials

Study design

This is a focused review article.

Objectives

This review presents important features of clinical outcomes assessments (COAs) in human spinal cord injury research. Considerations for COAs by trial phase and International Classification of Functioning, Disability and Health are presented as well as strengths and recommendations for upper extremity COAs for research. Clinical trial tools and designs to address recruitment challenges are identified.

Methods

The methods include a summary of topics discussed during a two-day workshop, conceptual discussion of upper extremity COAs and additional focused literature review.

Results

COAs must be appropriate to trial phase and particularly in mid-late-phase trials, should reflect recovery vs. compensation, as well as being clinically meaningful. The impact and extent of upper vs. lower motoneuron disease should be considered, as this may affect how an individual may respond to a given therapeutic. For trials with broad inclusion criteria, the content of COAs should cover all severities and levels of SCI. Specific measures to assess upper extremity function as well as more comprehensive COAs are under development. In addition to appropriate use of COAs, methods to increase recruitment, such as adaptive trial designs and prognostic modeling to prospectively stratify heterogeneous populations into appropriate cohorts should be considered.

Conclusions

With an increasing number of clinical trials focusing on improving upper extremity function, it is essential to consider a range of factors when choosing a COA.

Sponsors

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

Motoneuron Death after Human Spinal Cord Injury

The severe muscle weakness and atrophy measured after human spinal cord injury (SCI) may relate to chronic muscle denervation due to motoneuron death and/or altered muscle use. The aim of this study was to estimate motoneuron death after traumatic human SCI. The diameter and number of myelinated axons were measured in ventral roots post-mortem because ventral roots contain large diameter (> 7 μm) myelinated axons that typically arise from motoneurons and innervate skeletal muscle. In four cases (SCI levels C7, C8, T4, and L1) involving contusion (n = 3) or laceration (n = 1), there was a significant reduction in the number of large diameter myelinated axons at the lesion epicenter (mean ± standard error [SE]: 45 ± 11% Uninjured), one level above (51 ± 14%), and one (27 ± 12%), two (45 ± 40%), and three (54 ± 23%) levels below the epicenter. Reductions in motoneuron numbers varied by side and case. These deficits result from motoneuron death because the gray matter was destroyed at and near the lesion epicenter. Muscle denervation must ensue. In seven cases, ventral roots at or below the epicenter had large diameter myelinated axons with unusually thin myelin, a sign of incomplete remyelination. The mean ± SE g ratio (axon diameter/fiber diameter) was 0.60 ± 0.01 for axons of all diameters in five above-lesion ventral roots, but increased significantly for large diameter fibers (≥ 12 μm) in three roots at the lesion epicenter. Motoneuron death after human SCI will coarsen muscle force gradation and control, while extensive muscle denervation will stifle activity-based treatments.

Does therapeutic electrical stimulation improve function in children with disabilities? A comprehensive literature review

The use of therapeutic electrical stimulation for medical purposes is not new; it has been described in medical textbooks since the 18th century, but its use has been limited due to concerns for tolerance and lack of research showing efficacy. The purpose of this review is to discuss the potential clinical applicability, while clarifying the differences in electrical stimulation (ES) treatments and the theory behind potential benefits to remediate functional impairments in youth.The literature review was performed as follows: A total of 37 articles were reviewed and the evidence for use in pediatric diagnoses is reported.The synthesis of the literature suggests that improvements in various impairments may be possible with the integration of ES. Most studies were completed on children with cerebral palsy (CP). Electrical stimulation may improve muscle mass and strength, spasticity, passive range of motion (PROM), upper extremity function, walking speed, and positioning of the foot and ankle kinematics during walking. Sitting posture and static/dynamic sitting balance may be improved with ES to trunk musculature. Bone mineral density may be positively affected with the use of Functional Electrical Stimulation (FES) ergometry. ES may also be useful in the management of urinary tract dysfunction and chronic constipation. Among all reviewed studies, reports of direct adverse reactions to electrical stimulation were rare.In conclusion, NMES and FES appear to be safe and well tolerated in children with various disabilities. It is suggested that physiatrists and other healthcare providers better understand the indications and parameters in order to utilize these tools effectively in the pediatric population. MeSH terms: Electrical stimulation; child; review.

Strength-Duration Curves of the Common Fibular Nerve Show Hypoexcitability in People With Functional Ankle Instability

BACKGROUND

Some motor impairments, such as decreased reaction of peroneal muscles, altered kinematics, or poor postural control, have been described in people with functional ankle instability. Evidence shows a possible relationship between fibular nerve impairments and functional ankle instability.

OBJECTIVE

To investigate the electrophysiologic excitability of the common fibular nerve, as measured by strength-duration curves, in subjects with functional ankle instability compared with a control group without ankle impairment.

DESIGN

A cross-sectional study.

SETTING

University Research laboratory.

PARTICIPANTS

Fifty subjects with functional ankle instability (35 men, 15 women; ages 24.36 ± 5.01 years) and 63 uninjured control patients (44 men, 19 women; ages 22.67 ± 4.85 years) were recruited by convenience sampling.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Strength-duration curves of the common fibular nerve were made in all participants. Rheobase, chronaxie, Bawen index, accommodation index, galvano-tetanic threshold, and intensity thresholds for different pulse durations were obtained and compared between the 2 groups.

RESULTS

Subjects with functional ankle instability show increased values of chronaxie (0.58 ± 0.24 ms versus 0.47 ± 0.16 ms; P = .004), Bawen index (1.53 ± 0.24 versus 1.39 ± 0.21; P = .002), and intensity thresholds for pulse durations ≤2 ms both for rectangular and triangular pulse wave forms. The accommodation index was smaller in subjects with functional ankle instability than controls (3.7 ± 0.72 versus 4.05 ± 0.98; P = .036). The remaining parameters did not show significant differences between groups.

CONCLUSIONS

These findings suggest that subjects with functional ankle instability show a decreased excitability in their common fibular nerve when compared with subjects without ankle injuries.

Age at spinal cord injury determines muscle strength

As individuals with spinal cord injury (SCI) age they report noticeable deficits in muscle strength, endurance and functional capacity when performing everyday tasks. These changes begin at ~45 years. Here we present a cross-sectional analysis of paralyzed thenar muscle and motor unit contractile properties in two datasets obtained from different subjects who sustained a cervical SCI at different ages (≤46 years) in relation to data from uninjured age-matched individuals. First, completely paralyzed thenar muscles were weaker when C6 SCI occurred at an older age. Muscles were also significantly weaker if the injury was closer to the thenar motor pools (C6 vs. C4). More muscles were strong (>50% uninjured) in those injured at a younger (≤25 years) vs. young age (>25 years), irrespective of SCI level. There was a reduction in motor unit numbers in all muscles tested. In each C6 SCI, only ~30 units survived vs. 144 units in uninjured subjects. Since intact axons only sprout 4-6 fold, the limits for muscle reinnervation have largely been met in these young individuals. Thus, any further reduction in motor unit numbers with time after these injuries will likely result in chronic denervation, and may explain the late-onset muscle weakness routinely described by people with SCI. In a second dataset, paralyzed thenar motor units were more fatigable than uninjured units. This gap widened with age and will reduce functional reserve. Force declines were not due to electromyographic decrements in either group so the site of failure was beyond excitation of the muscle membrane. Together, these results suggest that age at SCI is an important determinant of long-term muscle strength, and fatigability, both of which influence functional capacity.

Human spinal cord injury: motor unit properties and behaviour

Spinal cord injury (SCI) results in widespread variation in muscle function. Review of motor unit data shows that changes in the amount and balance of excitatory and inhibitory inputs after SCI alter management of motoneurons. Not only are units recruited up to higher than usual relative forces when SCI leaves few units under voluntary control, the force contribution from recruitment increases due to elevation of twitch/tetanic force ratios. Force gradation and precision are also coarser with reduced unit numbers. Maximal unit firing rates are low in hand muscles, limiting voluntary strength, but are low, normal or high in limb muscles. Unit firing rates during spasms can exceed voluntary rates, emphasizing that deficits in descending drive limit force production. SCI also changes muscle properties. Motor unit weakness and fatigability seem universal across muscles and species, increasing the muscle weakness that arises from paralysis of units, motoneuron death and sensory impairment. Motor axon conduction velocity decreases after human SCI. Muscle contractile speed is also reduced, which lowers the stimulation frequencies needed to grade force when paralysed muscles are activated with patterned electrical stimulation. This slowing does not necessarily occur in hind limb muscles after cord transection in cats and rats. The nature, duration and level of SCI underlie some of these species differences, as do variations in muscle function, daily usage, tract control and fibre-type composition. Exploring this diversity is important to promote recovery of the hand, bowel, bladder and locomotor function most wanted by people with SCI.

Hybrid brain-computer interfaces and hybrid neuroprostheses for restoration of upper limb functions in individuals with high-level spinal cord injury

BACKGROUND

The bilateral loss of the grasp function associated with a lesion of the cervical spinal cord severely limits the affected individuals' ability to live independently and return to gainful employment after sustaining a spinal cord injury (SCI). Any improvement in lost or limited grasp function is highly desirable. With current neuroprostheses, relevant improvements can be achieved in end users with preserved shoulder and elbow, but missing hand function.

OBJECTIVE

The aim of this single case study is to show that (1) with the support of hybrid neuroprostheses combining functional electrical stimulation (FES) with orthoses, restoration of hand, finger and elbow function is possible in users with high-level SCI and (2) shared control principles can be effectively used to allow for a brain-computer interface (BCI) control, even if only moderate BCI performance is achieved after extensive training.

PATIENT AND METHODS

The individual in this study is a right-handed 41-year-old man who sustained a traumatic SCI in 2009 and has a complete motor and sensory lesion at the level of C4. He is unable to generate functionally relevant movements of the elbow, hand and fingers on either side. He underwent extensive FES training (30-45min, 2-3 times per week for 6 months) and motor imagery (MI) BCI training (415 runs in 43 sessions over 12 months). To meet individual needs, the system was designed in a modular fashion including an intelligent control approach encompassing two input modalities, namely an MI-BCI and shoulder movements.

RESULTS

After one year of training, the end user's MI-BCI performance ranged from 50% to 93% (average: 70.5%). The performance of the hybrid system was evaluated with different functional assessments. The user was able to transfer objects of the grasp-and-release-test and he succeeded in eating a pretzel stick, signing a document and eating an ice cream cone, which he was unable to do without the system.

CONCLUSION

This proof-of-concept study has demonstrated that with the support of hybrid FES systems consisting of FES and a semiactive orthosis, restoring hand, finger and elbow function is possible in a tetraplegic end-user. Remarkably, even after one year of training and 415 MI-BCI runs, the end user's average BCI performance remained at about 70%. This supports the view that in high-level tetraplegic subjects, an initially moderate BCI performance cannot be improved by extensive training. However, this aspect has to be validated in future studies with a larger population.

Electrical stimulation of embryonic neurons for 1 hour improves axon regeneration and the number of reinnervated muscles that function

Motoneuron death after spinal cord injury or disease results in muscle denervation, atrophy, and paralysis. We have previously transplanted embryonic ventral spinal cord cells into the peripheral nerve to reinnervate denervated muscles and to reduce muscle atrophy, but reinnervation was incomplete. Here, our aim was to determine whether brief electrical stimulation of embryonic neurons in the peripheralnerve changes motoneuron survival, axon regeneration, and muscle reinnervation and function because neural depolarization is crucial for embryonic neuron survival and may promote activity-dependent axon growth. At 1 week after denervation by sciatic nerve section, embryonic day 14 to 15 cells were purified for motoneurons, injected into the tibial nerve of adult Fischer rats, and stimulated immediatelyfor up to 1 hour. More myelinated axons were present in tibial nerves 10 weeks after transplantation when transplants had been stimulated acutely at 1 Hz for 1 hour. More muscles were reinnervated if the stimulation treatment lasted for 1 hour. Reinnervation reduced muscle atrophy, with or without the stimulation treatment. These data suggest that brief stimulation of embryonic neurons promotes axon growth, which has a long-term impact on muscle reinnervation and function. Muscle reinnervation is important because it may enable the use of functional electrical stimulation to restore limb movements.

Functional electrical stimulation in spinal cord injury:: from theory to practice

This article outlines steps to practical application of functional electrical stimulation (FES) within activity-based restorative therapy (ABRT). Drawing from current evidence, specific applications of FES intended to help restore function lost to spinal cord injury and associated neurologic disease are discussed. The medical and therapeutic indications, precautions, and contraindications are reviewed to help participants with appropriate patient selection, treatment planning, and assessment. Also included are the physiological implications of FES and alterable parameters, including dosing and timing, for a desired response. Finally, approaches to improve cortical representation and motor learning and to transition emerging movement into functional tasks are reviewed.

Do additional inputs change maximal voluntary motor unit firing rates after spinal cord injury?

BACKGROUND

Motor unit firing frequencies are low during maximal voluntary contractions (MVCs) of human thenar muscles impaired by cervical spinal cord injury (SCI).

OBJECTIVE

This study aimed to examine whether thenar motor unit firing frequencies increase when driven by both maximal voluntary drive and other concurrent inputs compared with an MVC alone.

METHODS

Motor unit firing rates, force, and surface electromyographic activity (EMG) were compared across 2 contractions: (a) MVC alone and (b) MVC combined with another input (combination contraction). Other inputs (conditions) included vibration, heat, or cold applied to the anterior surface of the forearm, electrical stimulation delivered to the anterior surface of the middle finger, a muscle spasm, or a voluntary contraction of the contralateral thenar muscles against resistance.

RESULTS

The maximal firing frequency (n = 68 units), force, and electromyographic activity (n = 92 contraction pairs) were all significantly higher during the combined contractions compared with MVCs alone. There was a 3-way interaction between contraction, condition, and subject for maximal motor unit firing rates, force, and EMG. Thus, combined contraction responses were different for conditions across subjects. Some conditions (eg, a muscle spasm) resulted in more effective and more frequent responses (increases in unit firing frequency, force, EMG in >50% contractions) than others. Recruitment of new units also occurred in combined contractions.

CONCLUSIONS

Motoneurons are still responsive to additional afferent inputs from various sources when rate modulation from voluntary drive is limited by SCI. Individuals with SCI may be able to combine inputs to control functional tasks they cannot perform with voluntary drive alone.

Nerve transfers in tetraplegia I: Background and technique

BACKGROUND

The recovery of hand function is consistently rated as the highest priority for persons with tetraplegia. Recovering even partial arm and hand function can have an enormous impact on independence and quality of life of an individual. Currently, tendon transfers are the accepted modality for improving hand function. In this procedure, the distal end of a functional muscle is cut and reattached at the insertion site of a nonfunctional muscle. The tendon transfer sacrifices the function at a lesser location to provide function at a more important location. Nerve transfers are conceptually similar to tendon transfers and involve cutting and connecting a healthy but less critical nerve to a more important but paralyzed nerve to restore its function.

METHODS

We present a case of a 28-year-old patient with a C5-level ASIA B (international classification level 1) injury who underwent nerve transfers to restore arm and hand function. Intact peripheral innervation was confirmed in the paralyzed muscle groups corresponding to finger flexors and extensors, wrist flexors and extensors, and triceps bilaterally. Volitional control and good strength were present in the biceps and brachialis muscles, the deltoid, and the trapezius. The patient underwent nerve transfers to restore finger flexion and extension, wrist flexion and extension, and elbow extension. Intraoperative motor-evoked potentials and direct nerve stimulation were used to identify donor and recipient nerve branches.

RESULTS

The patient tolerated the procedure well, with a preserved function in both elbow flexion and shoulder abduction.

CONCLUSIONS

Nerve transfers are a technically feasible means of restoring the upper extremity function in tetraplegia in cases that may not be amenable to tendon transfers.

Scapular stabilization in patients with spinal cord injury

BACKGROUND

Severe scapular instability can be a considerable problem for people with high-level cervical spinal cord injury. Scapular instability reduces the effectiveness of the already weakened shoulder flexors and abductors, thereby limiting hand-to-mouth and hand-to-head activities. The winged scapula may cause inferior pole skin breakdown, as well as neck and shoulder pain.

OBJECTIVE

To report the efficacy of a fusionless scapular stabilization procedure as a means to enhance function in a consecutive group of patients with high-level cervical spinal cord injury.

METHODS

Four people with spinal cord injury at C4-C5 (2 male, 2 female; mean age = 17.3 years, range = 14-20 years) underwent scapular stabilization via scapulothoracic fusion (N=2) or by tethering the scapula to the rib cage with Mersilene tape as a fusionless stabilization (N=2). One patient died of unrelated causes 18 months after surgery, and the remaining 3 were followed for 26, 39, and 41 months, respectively. Data collection included radiographic analysis, active range of motion measures, and functional assessment.

RESULTS

Active shoulder flexion and abduction remained unchanged in 2 patients, but functional scores improved with regard to feeding and grooming capability. All patients reported satisfaction with postoperative appearance, and 3 patients reported considerable reduction in shoulder pain after surgery. Radiographs demonstrated maintenance of stable scapular alignment in all patients at final follow up. Wound breakdown, requiring removal of instrumentation, occurred in 2 patients.

CONCLUSION

Scapular stabilization with or without fusion is a viable option to improve appearance, pain, and upper extremity function in people with high-level tetraplegia and scapular instability.

Involuntary, electrically excitable nerve transfer for denervation: results from an animal model

PURPOSE

The purpose of this study was to evaluate the efficacy of "paralyzed" nerve transfer (ie, transfer of an involuntary, nondegenerated, electrically excitable nerve onto an involuntary, degenerated, non-electrically excitable nerve) and functional electrical stimulation for reinnervation. We hypothesized that lower motor neuron cell body continuity with the motor cortex, via intact upper motor neurons, is not necessary for reinnervation of the extremities.

METHODS

Fischer 344 rats had lower thoracic spinal cord injury (SCI) followed by unilateral tibial nerve transection and delayed peroneal ("paralyzed") to tibial nerve transfer (group A) or primary neurorrhaphy (group B). Control groups had SCI and a unilateral hindlimb incision and nerve exposure only (group C) or a unilateral hindlimb disection and transection of both the tibial and peroneal nerves (group D). Three months after surgery, the proximal peroneal (group A) or proximal tibial (groups B, C, and D) nerves were electrically stimulated in vivo, and gastrocnemius force production was measured on both the operative and nonoperative hindlimbs. In addition, the distal tibial nerves from both the experimental and control-side hindlimbs were sectioned and stained with anti-neurofilament protein to determine total axon counts.

RESULTS

Mean gastrocnemius force return and mean axonal regeneration was 47% and 51%, respectively, for group A animals (n = 9), 68% and 73% for group B animals (n = 4), 97% and 99% for group C animals (n = 4), and 0 and 2% for group D animals (n = 4). A 1-way analysis of variance for independent samples yielded significant differences between groups A, B, and C for gastrocnemius force return and between all groups for axonal regeneration.

CONCLUSIONS

Paralyzed nerve transfer produces a mean of approximately 50% return of gastrocnemius force and axonal regeneration. Paralyzed nerve transfer combined with functional electrical stimulation is a viable method for reanimating denervated motor units in the setting of SCI.

A pilot study of observational motor assessment in infants and toddlers with spinal cord injury

PURPOSE

To examine the reliability of an observational movement assessment in infants and children with spinal cord injury (SCI) by evaluating interrater agreement of joint actions assessed in the International Standards for Neurological Classification of Spinal Cord Injury using the Active Movement Scale testing technique and scoring criteria.

METHODS

A series of 5 consecutive children with SCI aged 12 months to 4 years were enrolled in this pilot study to evaluate interrater agreement of observational movement.

RESULTS

There was high agreement of examination scores for unimpaired muscles and completely paralyzed muscles in strength comparisons between the 2 examiners. There was much less agreement of examination scores of partially intact muscles.

CONCLUSION

Observational movement assessment may be one component of assessing motor function in infants and toddlers with SCI, but additional work must be done.

Musculoskeletal model-guided, customizable selection of shoulder and elbow muscles for a C5 SCI neuroprosthesis

Individuals with C5/C6 spinal cord injury (SCI) have a number of paralyzed muscles in their upper extremities that can be electrically activated in a coordinated manner to restore function. The selection of a practical subset of paralyzed muscles for stimulation depends on the specific condition of the individual, the functions targeted for restoration, and surgical considerations. This paper presents a musculoskeletal model-based approach for optimizing the muscle set used for functional electrical stimulation (FES) of the shoulder and elbow in this population. Experimentally recorded kinematics from able-bodied subjects served as inputs to a musculoskeletal model of the shoulder and elbow, which was modified to reflect the reduced muscle force capacities of an individual with C5 SCI but also the potential of using FES to activate paralyzed muscles. A large number of inverse dynamic simulations mimicking typical activities of daily living were performed that included 1) muscles with retained voluntary control and 2) many different combinations of stimulated paralyzed muscles. These results indicate that a muscle set consisting of the serratus anterior, infraspinatus and triceps would enable the greatest range of relevant movements. This set will become the initial target in a C5SCI neuroprosthesis to restore shoulder and elbow function.

La fatigue du blessé médullaire

OBJECTIVES

To identify variables increasing fatigue following spinal cord injury (SCI) and their functional consequences.

METHODS

A search of the Medline and Reedoc databases with the keywords SCI, fatigue, intrinsic muscular fatigue, chronic fatigue, aging, training, electrostimulation, quality of life and the same words in French.

RESULTS

Two kinds of fatigue are identified following SCI. Intrinsic fatigue in muscles totally or partially paralysed at the level of or below the spinal cord lesion; this peripheral fatigue is due to denervation, total or partial loss of motoneurons, or histological and metabolical changes in muscle; it is well-defined by electrophysiological technology; spasticity and spasms have little influence on its development; it is reversible in part with long term electrostimulation, but at this time, electroneuroprosthetic techniques do not reduce the excessive energetic cost to stand up and walk. Chronic fatigue appears in the long term following SCI; it is linked with aging, physiological, and psychological deconditioning; some data point to chronic fatigue after SCI similar to post-polio syndrome and chronic fatigue syndrome, which may explain the central nature of the fatigue; training programs could be useful in delaying this chronic fatigue and as a consequence, increasing the latent quality of life.

CONCLUSION

Muscular intrinsic fatigue after SCI is always of a peripherical nature in muscles partially or totally paralysed. Chronic fatigue during aging greatly decreases quality of life. Both intrinsic and chronic fatigue could be anticipated by electrostimulation technique on the one hand and long term training on the other.

Fatigue of muscles weakened by death of motoneurons

Weakness is a characteristic of muscles influenced by the postpolio syndrome (PPS), amyotrophic lateral sclerosis (ALS), and spinal cord injury (SCI). The strength deficits relate to changes in muscle use and to the chronic denervation that can follow the spinal motoneuron death common to these disorders. PPS, ALS, and SCI also involve variable amounts of supraspinal neuron death, the effects of which on muscle weakness remains unclear. Nevertheless, weakness of muscle itself defines the functional consequences of these disorders. A weaker muscle requires an individual to work that muscle at higher than usual intensities relative to its maximal capacity, inducing progressive fatigue and an increased sense of effort. Little evidence is available to suggest that the fatigue commonly experienced by individuals with these disorders relates to an increase in the intrinsic fatigability of the muscle fibers. The only exception is when SCI induces chronic muscle paralysis. To reduce long-term functional deficits in these disorders, studies must identify the signaling pathways that influence neuron survival and determine the factors that encourage and limit sprouting of motor axons. This may ensure that a greater proportion of the fibers in each muscle remain innervated and available for use.

Patterns of lower extremity innervation in pediatric spinal cord injury

STUDY DESIGN

Retrospective review.

OBJECTIVES

To identify relationships between lower extremity innervation and level of injury, mechanism of injury, and age at injury in a pediatric population with spinal cord injury (SCI). Secondarily, relationships between innervation and completeness of injury, time since injury, race, and sex were evaluated.

SETTING

Pediatric orthopedic referral hospital, Philadelphia, Pennsylvania.

METHODS

Records of 190 subjects, ages 1-21 years, were reviewed. Data collected from the medical record included lower extremity muscle innervation, American Spinal Injury Association (ASIA) level and class, mechanism of injury, age at injury, time since injury, race, and sex. To determine innervation, lower extremity muscles had been tested using surface electrical stimulation and identified as being innervated or denervated. If a muscle responded weakly, strength duration testing was performed. For analysis via logistic regression, subjects were grouped based upon level and mechanism of injury.

RESULTS

A relationship (P<0.0001) was found between ASIA level and lower extremity innervation of all muscles and between length of time since injury and lower extremity innervation for some muscles. Following multiple logistic regression, only ASIA level remained as an independent predictor of lower extremity innervation status.

CONCLUSION

Our results show that lower extremity innervation does differ based on the level of the injury. Denervation began to be seen with injuries in the lower thoracic region and more predominantly with injuries in the lumbar region. This supports our hypothesis that the incidence of lower motor neuron injuries would increase as injuries became more caudal. Our hypotheses of a relationship between innervation status and mechanism of injury and age at injury were not supported. This information is important in determining treatment strategies, eligibility for electrical stimulation techniques, and potential regenerative strategies.

SPONSORSHIP

This study was funded by Shriners Hospitals for Children, Grant #8530.

Exercise as a Health-Promoting Activity Following Spinal Cord Injury

Spinal cord injury is a catastrophic event that immeasurably alters activity and health. Depending on the level and severity of injury, functional and homeostatic decline of many body systems can be anticipated in a large segment of the paralyzed population. The level of physical inactivity and deconditioning imposed by SCI profoundly contrasts the preinjury state in which most individuals are relatively young and physically active. Involvement in sports, recreation, and therapeutic exercise is commonly restricted after SCI by loss of voluntary motor control, as well as autonomic dysfunction, altered fuel homeostasis, inefficient temperature regulation, and early-onset muscle fatigue. Participation in exercise activities also may require special adaptive equipment and, in some instances, the use of electrical current either with or without computerized control. Notwithstanding these limitations, considerable evidence supports the belief that recreational and therapeutic exercise improves the physical and emotional well-being of participants with SCI. This article will examine multisystem decline and the need for exercise after SCI. It will further examine how exercise might be used as a tool to enhance health by slowing multisystem medical complications unique to those with SCI. As imprudent exercise recommendations may pose avoidable risks of incipient disability, orthopedic deterioration, or pain, the special risks of exercise misuse in those with SCI will be discussed.

Tendon reflexes for predicting movement recovery after acute spinal cord injury in humans

OBJECTIVE

Use the tendon reflex to examine spinal cord excitability after acute spinal cord injury (SCI), relating excitability findings to prognosis.

METHODS

We conducted repeated measures of reflex responses to mechanical taps at the patellar and Achilles tendons of the lower limbs, and the wrist flexor tendons of the upper limbs in persons with acute SCI, beginning as early as the day of injury. The single largest EMG response (peak-to-peak) for each site was recorded. Subjects were compared based on level of injury and final neurologic status of lower limb motor function (i.e. absence of any voluntary recruitment in a lower limb muscle: motor-complete; voluntary recruitment in 1 or more lower-limb muscles: motor-incomplete).

RESULTS

We studied 229 subjects with acute SCI. Persons with injury to the cervical or thoracic spinal cord and who were (or became) motor-incomplete showed large tendon responses, even at the time of initial evaluation. In combination with larger tendon response amplitudes, the presence of the 'crossed-adductor' response to patellar tendon taps at the acute stage was highly predictive of functional motor recovery following SCI. In marked contrast, tendon responses were small (e.g. < 0.1 mV) or absent in persons with acute, motor-complete injury (and which remained motor-complete), and the crossed-adductor response was never seen. Reflex amplitudes and the incidence of the crossed-adductor response increased somewhat over time in persons with motor-complete SCI, but did not approach the values seen in motor-incomplete subjects.

CONCLUSIONS

Taken together, tendon response amplitude and reflex spread were sensitive and specific indicators of preserved supraspinal control over lower limb musculature in subjects with acute SCI. A simple algorithm using these outcome measures predicted a 'motor-complete' status with 100% accuracy, and a motor-incomplete status with accuracy exceeding 91%.

Implanted neuroprostheses for restoration of hand function in tetraplegic patients

Restoration of hand function through functional electrical stimulation allows tetraplegic patients to use existing abilities to control paralyzed muscles. In patients with C5 or C6 spinal cord injuries, implanted upper extremity neuroprostheses use functional electrical stimulation technology to power hand and arm muscles. A variety of devices, often using contralateral shoulder motion, sends signals via a small external controller and transmitting coil to an implanted stimulator. The stimulator powers designated upper extremity muscles via implanted electrodes. The surgical procedure is minimally invasive and easily reversed. Palmar and lateral grasp, among other functions, can be reliably restored, leading to significant improvements in functional capacity. High user satisfaction, low complication rates, and recent advances in technology and control systems contribute to the success of this technology in the treatment of devastating spinal cord injuries.

Exercise Recommendations for Individuals with Spinal Cord Injury

Persons with spinal cord injury (SCI) exhibit deficits in volitional motor control and sensation that limit not only the performance of daily tasks but also the overall activity level of these persons. This population has been characterised as extremely sedentary with an increased incidence of secondary complications including diabetes mellitus, hypertension and atherogenic lipid profiles. As the daily lifestyle of the average person with SCI is without adequate stress for conditioning purposes, structured exercise activities must be added to the regular schedule if the individual is to reduce the likelihood of secondary complications and/or to enhance their physical capacity. The acute exercise responses and the capacity for exercise conditioning are directly related to the level and completeness of the spinal lesion. Appropriate exercise testing and training of persons with SCI should be based on the individual's exercise capacity as determined by accurate assessment of the spinal lesion. The standard means of classification of SCI is by application of the International Standards for Classification of Spinal Cord Injury, written by the Neurological Standards Committee of the American Spinal Injury Association. Individuals with complete spinal injuries at or above the fourth thoracic level generally exhibit dramatically diminished cardiac acceleration with maximal heart rates less than 130 beats/min. The work capacity of these persons will be limited by reductions in cardiac output and circulation to the exercising musculature. Persons with complete spinal lesions below the T(10) level will generally display injuries to the lower motor neurons within the lower extremities and, therefore, will not retain the capacity for neuromuscular activation by means of electrical stimulation. Persons with paraplegia also exhibit reduced exercise capacity and increased heart rate responses (compared with the non-disabled), which have been associated with circulatory limitations within the paralysed tissues. The recommendations for endurance and strength training in persons with SCI do not vary dramatically from the advice offered to the general population. Systems of functional electrical stimulation activate muscular contractions within the paralysed muscles of some persons with SCI. Coordinated patterns of stimulation allows purposeful exercise movements including recumbent cycling, rowing and upright ambulation. Exercise activity in persons with SCI is not without risks, with increased risks related to systemic dysfunction following the spinal injury. These individuals may exhibit an autonomic dysreflexia, significantly reduced bone density below the spinal lesion, joint contractures and/or thermal dysregulation. Persons with SCI can benefit greatly by participation in exercise activities, but those benefits can be enhanced and the relative risks may be reduced with accurate classification of the spinal injury.

Injured metamere and functional surgery of the tetraplegic upper limb

The size of injured metamere (IM) in tetraplegia exhibits a high variability that explains the different clinical presentations in patients who have the same neurologic level. Even when functional electrical stimulation is not planned, the lower motor neuron (LMN) integrity of paralyzed muscles must be evaluated, especially in patients with high-level tetraplegia. During the acute phase, detecting the size of the IM is important to prevent supination contracture and stiffness of the thumb and finger joints. When planning functional surgery, the LMN integrity of intrinsic muscles helps the surgeon adapt his surgical procedures. Assessing IM size must be integrated systematically into the evaluation of tetraplegic patients.

Indications and future directions for upper limb neuroprostheses in tetraplegic patients: a review

The development of the upper extremity neuroprosthesis has been a challenging and rewarding contribution to the management of the SCI patient. The authors' experience and that of their clinical trial teams has verified that this technology is a strong alternative to conventional reconstruction and conservative management. In the future, even more powerful tools will emerge from the laboratory as these devices and collaborative surgical procedures evolve.