Extensor spasms triggered by imposed knee extension in chronic human spinal cord injury

Muscle Excitability Scale for the assessment of spastic reflexes in spinal cord injury: development and evaluation

STUDY DESIGN

A psychometric study.

OBJECTIVES

To introduce a novel simple tool designed to evaluate the intensity of the phasic (dynamic) component of spastic motor behavior in spinal cord injury (SCI) people and to assess its reliability and validity.

SETTING

The study was developed in the Spinal Cord Unit at University Hospital Motol and Paraple Centre in Prague, Czech Republic.

METHODS

The Muscle Excitability Scale (MES) is designed to rate muscle motor response to exteroceptive and proprioceptive stimuli. The impairment rating ranges from zero muscle/muscle group spasm or clonus to generalized spastic response. The selected 0 to 4 scale allows for comparing the MES results with those of the Modified Ashworth Scale (MAS). After long-term use and repeated revisions, a psychometric analysis was conducted. According to the algorithm, two physiotherapists examined 50 individuals in the chronic stage after SCI.

RESULTS

The inter-rater reliability of MES for both legs showed κ = 0.52. The intra-rater reliability of MES for both legs showed κ = 0.50. The inter-rater reliability of simultaneously assessed MAS for both legs was higher, with κ = 0.69. The intra-rater reliability of MAS for both legs showed κ = 0.72. Spearman's rank correlation coefficient between MES and spasm frequency of Penn Spasm Frequency Scale (PSFS) was low, while the correlation coefficient between MES and the severity part of PSFS was moderate.

CONCLUSIONS

The MES is a complementary tool for assessing the dynamic component of spastic motor behavior in SCI people. It allows a more comprehensive clinical characterization of spastic reflexes when used along with the MAS.

Muscle Spasms after Spinal Cord Injury Stem from Changes in Motoneuron Excitability and Synaptic Inhibition, Not Synaptic Excitation

Muscle spasms are common in chronic spinal cord injury (SCI), posing challenges to rehabilitation and daily activities. Pharmacological management of spasms mostly targets suppression of excitatory inputs, an approach known to hinder motor recovery. To identify better targets, we investigated changes in inhibitory and excitatory synaptic inputs to motoneurons as well as motoneuron excitability in chronic SCI. We induced either a complete or incomplete SCI in adult mice of either sex and divided those with incomplete injury into low or high functional recovery groups. Their sacrocaudal spinal cords were then extracted and used to study plasticity below injury, with tissue from naive animals as a control. Electrical stimulation of the dorsal roots elicited spasm-like activity in preparations of chronic severe SCI but not in the control. To evaluate overall synaptic inhibition activated by sensory stimulation, we measured the rate-dependent depression of spinal root reflexes. We found inhibitory inputs to be impaired in chronic injury models. When synaptic inhibition was blocked pharmacologically, all preparations became clearly spastic, even the control. However, preparations with chronic injuries generated longer spasms than control. We then measured excitatory postsynaptic currents (EPSCs) in motoneurons during sensory-evoked spasms. The data showed no difference in the amplitude of EPSCs or their conductance among animal groups. Nonetheless, we found that motoneuron persistent inward currents activated by the EPSCs were increased in chronic SCI. These findings suggest that changes in motoneuron excitability and synaptic inhibition, rather than excitation, contribute to spasms and are better suited for more effective therapeutic interventions.Significance Statement Neural plasticity following spinal cord injury is crucial for recovery of motor function. Unfortunately, this process is blemished by maladaptive changes that can cause muscle spasms. Pharmacological alleviation of spasms without compromising the recovery of motor function has proven to be challenging. Here, we investigated changes in fundamental spinal mechanisms that can cause spasms post-injury. Our data suggest that the current management strategy for spasms is misdirected toward suppressing excitatory inputs, a mechanism that we found unaltered after injury, which can lead to further motor weakness. Instead, this study shows that more promising approaches might involve restoring synaptic inhibition or modulating motoneuron excitability.

Rare phenomena of central rhythm and pattern generation in a case of complete spinal cord injury

Lumbar central pattern generators (CPGs) control the basic rhythm and coordinate muscle activation underlying hindlimb locomotion in quadrupedal mammals. The existence and function of CPGs in humans have remained controversial. Here, we investigated a case of a male individual with complete thoracic spinal cord injury who presented with a rare form of self-sustained rhythmic spinal myoclonus in the legs and rhythmic activities induced by epidural electrical stimulation (EES). Analysis of muscle activation patterns suggested that the myoclonus tapped into spinal circuits that generate muscle spasms, rather than reflecting locomotor CPG activity as previously thought. The EES-induced patterns were fundamentally different in that they included flexor-extensor and left-right alternations, hallmarks of locomotor CPGs, and showed spontaneous errors in rhythmicity. These motor deletions, with preserved cycle frequency and period when rhythmic activity resumed, were previously reported only in animal studies and suggest a separation between rhythm generation and pattern formation. Spinal myoclonus and the EES-induced activity demonstrate that the human lumbar spinal cord contains distinct mechanisms for generating rhythmic multi-muscle patterns.

Properties of the surface electromyogram following traumatic spinal cord injury: a scoping review

Traumatic spinal cord injury (SCI) disrupts spinal and supraspinal pathways, and this process is reflected in changes in surface electromyography (sEMG). sEMG is an informative complement to current clinical testing and can capture the residual motor command in great detail-including in muscles below the level of injury with seemingly absent motor activities. In this comprehensive review, we sought to describe how the sEMG properties are changed after SCI. We conducted a systematic literature search followed by a narrative review focusing on sEMG analysis techniques and signal properties post-SCI. We found that early reports were mostly focused on the qualitative analysis of sEMG patterns and evolved to semi-quantitative scores and a more detailed amplitude-based quantification. Nonetheless, recent studies are still constrained to an amplitude-based analysis of the sEMG, and there are opportunities to more broadly characterize the time- and frequency-domain properties of the signal as well as to take fuller advantage of high-density EMG techniques. We recommend the incorporation of a broader range of signal properties into the neurophysiological assessment post-SCI and the development of a greater understanding of the relation between these sEMG properties and underlying physiology. Enhanced sEMG analysis could contribute to a more complete description of the effects of SCI on upper and lower motor neuron function and their interactions, and also assist in understanding the mechanisms of change following neuromodulation or exercise therapy.

A framework for closing the loop between human experts and computational algorithms for the assessment of movement disorders

Clinical assessment of abnormal neuromechanics is typically performed by manipulation of the affected limbs; a process with low inter- and intra-rater reliability. This paper aims at formalizing a framework that closes the loop between a clinician's expertise and computational algorithms, to enhance the clinician's diagnostic capabilities during physical manipulation. The framework's premise is that the dynamics that can be measured by manipulation of a limb are distinct between movement disorders. An a priori database contains measurements encoded in a space called the information map. Based on this map, a computational algorithm identifies which probing motions are more likely to yield distinguishing information about a patient's movement disorder. The clinician executes this movement and the resulting dynamics, combined with clinician input, is used by the algorithm to estimate which of the movement disorders in the database are most probable. This is recursively repeated until a diagnosis can be confidently made. The main contributions of this paper are the formalization of the framework and the addition of the information map to select informative movements. The establishment of the framework provides a foundation for a standardized assessment of movement disorders and future work will aim at testing the framework's efficacy.

Impact of spasticity on transfers and activities of daily living in individuals with spinal cord injury

CONTEXT/OBJECTIVE

For persons with spinal cord injury, spasticity commonly interferes with activities of daily living such as transfers. Electromyography can be used to objectively measure muscle spasms during transfers, but how electromyographic measures relate to the impact spasticity has on life, or to clinically-rated spasticity, is unclear. We aimed to characterize relationships among spasm duration and magnitude, impact of spasticity on daily life, and a clinical measure of extensor spasticity, as well as to determine reliability of the electromyographic measures.

DESIGN

Participants (N=19) underwent electromyographic measurements of involuntary muscle activity (spasm duration and magnitude) evoked in quadriceps muscles during transfers on two days. Impact of spasticity on daily life was measured with the Spinal Cord Injury Spasticity Evaluation Tool. Clinically-rated spasticity severity was measured with the Spinal Cord Assessment Tool for Spastic reflexes.

RESULTS

No significant associations were found between impact of spasticity and spasm duration, spasm magnitude, or clinical extensor spasticity score. Absolute and normalized spasm duration were positively associated with clinical extensor spasticity score (rho=0.510-0.667, P < 0.05). Spasm measures during transfers had good to excellent day-to-day reliability (rho=0.656-0.846, P < 0.05).

CONCLUSIONS

Electromyographic and clinical measures of involuntary activity in the lower extremity do not significantly relate to perceived impact of spasticity on daily life. However, quadriceps spasm duration during transfers is related to clinically-rated extensor spasticity. Electromyography is a reliable method of quantifying quadriceps spasms during transfers. Future investigations should identify factors that influence the impact of spasticity on life, which may help direct treatment strategies to reduce problematic impact.

Treatment of spasticity in spinal cord injury with botulinum toxin

CONTEXT

Spasticity is one of the most frequent complications in spinal cord injury (SCI), and is routinely managed with oral pharmacologic therapy. Botulinum toxin (BT) is not accepted as a treatment for spasticity in SCI in Spain but may be used in certain cases of focal distribution.

OBJECTIVE

To report the results with BT for treatment of spasticity in SCI.

DESIGN AND SETTING

Descriptive retrospective study conducted at a specialist SCI rehabilitation center in Spain, covering patients first treated from 2012 through 2014, and successfully followed up for a minimum of 1 year. Data were collected on the following variables: demographic and SCI characteristics (level and grade); nature of spasticity, e.g. tone, distribution, spasms, articular involvement and pain; function; application of BT; tolerance and adverse reactions.

RESULTS

The study covered 90 patients, predominantly male with incomplete injuries. Improvement in tone as measured by the modified Ashworth scale was a mean of 1.17 points. Goniometric improvement was achieved in 65.6% and improvement in pain in 38.9% of cases. There were no adverse side-effects. Patients with focal spasticity showed a significantly greater improvement in tone (P < 0.0001). The earlier the BT injection, the greater the improvement in goniometric performance (P < 0.006) and pain (P < 0.033), with the best results being obtained within the first 6 months of clinical course. ASIA D injuries showed a greater improvement in tone (P < 0.0001).

CONCLUSIONS

BT can be both an effective treatment for focal spasticity in SCI and a good coadjuvant for oral treatments in generalized spasticity.

Hip proprioceptors preferentially modulate reflexes of the leg in human spinal cord injury

Stretch-sensitive afferent feedback from hip muscles has been shown to trigger long-lasting, multijoint reflex responses in people with chronic spinal cord injury (SCI). These reflexes could have important implications for control of leg movements during functional activities, such as walking. Because the control of leg movement relies on reflex regulation at all joints of the limb, we sought to determine whether stretch of hip muscles modulates reflex activity at the knee and ankle and, conversely, whether knee and ankle stretch afferents affect hip-triggered reflexes. A custom-built servomotor apparatus was used to stretch the hip muscles in nine chronic SCI subjects by oscillating the legs about the hip joint bilaterally from 10° of extension to 40° flexion. To test whether stretch-related feedback from the knee or ankle would be affected by hip movement, patellar tendon percussions and Achilles tendon vibration were delivered when the hip was either extending or flexing. Surface electromyograms (EMGs) and joint torques were recorded from both legs. Patellar tendon percussions and Achilles tendon vibration both elicited reflex responses local to the knee or ankle, respectively, and did not influence reflex responses observed at the hip. Rather, the movement direction of the hip modulated the reflex responses local to the joint. The patellar tendon reflex amplitude was larger when the perturbation was delivered during hip extension compared with hip flexion. The response to Achilles vibration was modulated by hip movement, with an increased tonic component during hip flexion compared with extension. These results demonstrate that hip-mediated sensory signals modulate activity in distal muscles of the leg and appear to play a unique role in modulation of spastic muscle activity throughout the leg in SCI.

Effects of multijoint spastic reflexes of the legs during assisted bilateral hip oscillations in human spinal cord injury

OBJECTIVE

To investigate the timing and magnitude of muscle activation during an active-assist bilateral hip motor task in human spinal cord injury (SCI).

DESIGN

A single test session using a novel robotic system to alternately flex and extend the hips from 40 degrees of hip flexion to 10 degrees of hip extension at 1 of 3 frequencies (.25, .50, .75Hz). Subjects were asked either to actively assist the movements or to remain relaxed during the imposed oscillations.

SETTING

All data were collected in a research laboratory.

PARTICIPANTS

Ten subjects with motor incomplete (American Spinal Injury Association grade C or D) SCI and 10 individuals without neurologic injury participated in this study.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Electromyograms and joint torques were recorded from the lower extremities of SCI subjects and compared with electromyograms and joint torque patterns recorded from 10 neurologically healthy individuals completing the same tasks.

RESULTS

In trials involving active assistance of the imposed hip oscillations, SCI subjects produced muscle activation patterns that were phased differently from muscle activity of neurologically intact subjects. SCI subjects generated peak torque at the end ranges of movement (ie, 40 degrees hip flexion, 10 degrees extension), whereas control subjects generated the greatest torque midway through the movements. Moreover, the phasing of active-assist hip torque in SCI subjects was similar to the phasing of reflexive hip torques produced during the unassisted condition (ie, SCI subjects instructed to relax), while control subjects produced no reflexive torques during unassisted trials.

CONCLUSIONS

The differences in the timing of muscle activity during the active-assist task in controls and SCI subjects highlights problems in generating appropriately timed muscle activity during ongoing movements. The similarity in muscle activity patterns for the active-assist and unassisted trials in SCI subjects further suggests that reflex feedback from hip afferents contributes substantially to muscle activation during active-assist movements. These findings demonstrate the disruptions in reflex regulation of movement in people with incomplete SCI and suggest that spastic reflexes might disrupt motor control.

Management of spasticity after spinal cord injury: current techniques and future directions

Spasticity, resulting in involuntary and sustained contractions of muscles, may evolve in patients with stroke, cerebral palsy, multiple sclerosis, brain injury, and spinal cord injury (SCI). The authors critically review the neural mechanisms that may contribute to spasticity after SCI and assess their likely degree of involvement and relative significance to its pathophysiology. Experimental data from patients and animal models of spasticity as well as computer simulations are evaluated. The current clinical methods used for the management of spasticity and the pharmacological actions of drugs are discussed in relation to their effects on spinal mechanisms. Critical assessment of experimental findings indicates that increased excitability of both motoneurons and interneurons plays a crucial role in pathophysiology of spasticity. New interventions, including forms of spinal electrical stimulation to suppress increased neuronal excitability, may reduce the severity of spasticity and its complications.

Perception of lower limb spasticity in patients with spinal cord injury

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

To study the manifestation of spasticity in daily life of the patients with spinal cord injury, their perception of spasticity and spasticity-related discomfort.

SETTING

Rehabilitation center in the Netherlands.

METHODS

Twenty-six patients with motor complete spinal cord injury (SCI) and spasticity in the lower limbs completed a questionnaire. The following outcome measures were used: manifestation of spasticity, activities during which spasticity occurs, perceived degree of spasticity and resulting discomfort, measured with visual analog scale (VAS) and Borg scale, respectively.

RESULTS

In general, spasticity manifested as extensor spasms (84.6%), flexor spasms and/or clonus (both 69.2%), and less often as continuous tension (57.7%). The registered activities were categorized into five main groups: 'changing position' was the largest group (22.0%) with a median VAS of 6.8 (range: 2.5-9.5) and median Borg scale of 3.0 (range: 1.0-7.0). Other groups of activities were 'making a transfer' (20.7%), 'activities of daily living' (17.1%), 'being active' (17.1%) and 'stable body position' (12.2%). The overall correlation between VAS and Borg was moderate (Spearman's rho=0.53, P=0.005).

CONCLUSIONS

Patients with complete SCI experienced several manifestations of spasticity, extensor spasms being the most common. Many daily life activities elicited different manifestations of spasticity. The experienced discomfort was only moderately related to the perceived degree of spasticity during an activity. Possibly, the discomfort is influenced by other factors than the perceived spasticity alone.

Rebound responses to prolonged flexor reflex stimuli in human spinal cord injury

The purpose of this study was to examine the reflex effects of electrical stimulation applied to the thigh using skin electrodes, targeting the sensory fibers of the rectus femoris and sartorius, in people with spinal cord injury (SCI). Thirteen individuals with SCI were recruited to participate in experiments using prolonged electrical stimuli on the right medial thigh over the regions of the sartorius and rectus femoris muscles. Three stimuli, spaced 20 s apart, were applied at 30 Hz for 1 s at four different intensities (15-60 mA) while subjects rested in a seated position. Isometric joint torques of the hip, knee and ankle, and electromyograms (EMGs) from six muscles of the leg were recorded during the stimulation. Early in the stimulation, a flexion response was observed at the hip and ankle, analogous to a flexor reflex; however, this response was usually followed by a "rebound" response consisting of hip extension, knee flexion and ankle plantarflexion, occurring in 10/13 subjects. Stimuli applied in a more lateral (mid thigh) electrode position (i.e. over the rectus femoris) were less effective in producing the response than medial placement, despite vigorous quadriceps activation. This complex reflex response is consistent with activation of a coordinating spinal circuit that could play a role in motor function. The reversal of the reflex pattern emphasizes the potential connection between skin/muscle afferents of the thigh, possibly including sartorius muscle afferents and locomotor reflex centers. This knowledge may be helpful in identifying rehabilitation strategies for enhancing gait training in human SCI.

Effectiveness of selective dorsal rhizotomy in 2 patients with progressive spasticity due to neurodegenerative disease

Selective dorsal rhizotomy at the lumbar level is a neurosurgical procedure, which reduces spasticity in the legs. Its effect has mainly been studied in children with spastic cerebral palsy. Little is known about the outcome of selective dorsal rhizotomy in patients with neurodegenerative disorders. We report the clinical course after selective dorsal rhizotomy in 2 patients with progressive spasticity. Leg spasticity was effectively and persistently reduced in both patients, facilitating care and improving sitting comfort. However, spasticity of the arms and other motor disturbances, such as spontaneous extension spasms and the ataxia, increased gradually in time. Selective dorsal rhizotomy leads to a disappearance of leg spasticity in patients with a neurodegenerative disease. Other motor signs are not influenced and may increase due to the progressive nature of the underlying disease.

Reflex response to imposed bilateral hip oscillations in human spinal cord injury

In human spinal cord injury (SCI), imposed unilateral hip movements trigger multijoint, coordinated reflexes that might incorporate interneuronal circuitry involved in normal motor control, such as neural pathways associated with the reflex control of locomotion. To further investigate the complexity of these hip-triggered reflexes, we measured the effects of kinematics of the contralateral hip on this type of spastic reflex activity in 11 chronic SCI subjects. A novel servomotor drive system was constructed to impose bilateral hip oscillations while the knees and ankles were held stationary in instrumented leg braces. Surface electromyograms (EMGs) and joint torques were recorded during the imposed hip oscillations. Tests were conducted at two different frequencies to test for velocity dependence of the reflexes and the following four paradigms were used to examine the effects of contralateral hip afferents on hip-triggered spastic reflexes: 1) bilateral alternating, 2) bilateral synchronous, 3) unilateral leg oscillation with the contralateral leg held stationary in hip extension, and 4) unilateral leg oscillation with the contralateral leg held stationary in hip flexion. The response to bilateral alternating movements resulted in a significantly larger reflex magnitude compared with the bilateral synchronous movements (P < 0.001). Unilateral leg perturbations yielded reflex patterns that were consistent with the reflex patterns observed during alternating and synchronous hip oscillations. These observations suggest that spastic reflex excitability is modulated through afferent input from the contralateral hip in a manner that is generally consistent with locomotion.

Spastic Reflexes Triggered by Ankle Load Release in Human Spinal Cord Injury

The rapid decrease in firing of load-sensitive group Ib muscle afferents during unloading may be particularly important in triggering the swing phase of gait. However, it still remains unclear whether load-sensitive muscle afferents modulate reflex activity in human spinal cord injury (SCI), as suggested by studies in the cat. The right hip of 12 individuals with chronic SCI was subjected to ramp (60°/s) and hold (10 s) movements over a range from 40° flexion to 0–10°extension using a custom servomotor system. An ankle dorsiflexion load was imposed and released after the hip reached a targeted position using a custom-designed pneumatic motor system. Isometric joint torques of the hip and knee, reaction torque of the ankle, and surface electromyograms (EMGs) from eight muscles of the leg were recorded following the imposed hip movement and ankle load release. Reflexes, characterized by hip flexion torque, knee extension, and coactivation of ankle flexors and extensors, were triggered by ankle load release when the hip was in an extended position. The ankle load release was observed to enhance the reflexes triggered by hip extension itself, suggesting that ankle load afferents play an important role in spastic reflexes in human SCI and that the reflex pathways associated with ankle load afferents have important implications in the spinal reflex regulation of human movement. Such muscle behaviors emphasize the role of ankle load afferents and hip proprioceptors on locomotion. This knowledge may be especially helpful in the treatment of spasms and in identifying rehabilitation strategies for producing functional movements in human SCI.

Flexor reflex responses triggered by imposed knee extension in chronic human spinal cord injury

Hypersensitivity of the flexor reflex pathways to input from force-sensitive muscle afferents may contribute to the prevalence and severity of muscle spasms in patients with spinal cord injury (SCI). In this study, we triggered flexor reflexes with constant velocity knee movements in 15 subjects with SCI. Ramp and hold knee extension perturbations were imposed on one leg while the hip and ankle were held in an isometric position using an instrumented leg brace. Knee, ankle and hip torque responses and electromyograms from six muscles of the leg were recorded following controlled knee extension at four different velocities. Tests were conducted with the hip in both flexed and extended positions. During the movement into knee extension, a velocity-dependent stretch reflex, represented by a progressively increasing knee flexion torque, was observed. In addition, another type of reflex that resembled a flexor reflex (flexion of the hip and ankle) was also triggered by the imposed knee extension. The magnitude of the ankle dorsiflexion torque responses was significantly correlated to the stretch reflex torque at the knee in 9 of the 15 subjects. We concluded that stretch reflexes initiate a muscle contraction that then can contribute to a flexor reflex response, possibly through muscle group III/IV afferent pathways. These results suggest that spasticity in SCI consists of a myriad of complex reflex responses that extend beyond stretch reflexes.