Disrupted Ankle Control and Spasticity in Persons With Spinal Cord Injury: The Association Between Neurophysiologic Measures and Function. A Scoping Review

Abstract

Control of muscles about the ankle joint is an important component of locomotion and balance that is negatively impacted by spinal cord injury (SCI). Volitional control of the ankle dorsiflexors (DF) is impaired by damage to pathways descending from supraspinal centers. Concurrently, spasticity arising from disrupted organization of spinal reflex circuits, further erodes control. The association between neurophysiological changes (corticospinal and spinal) with volitional ankle control (VAC) and spasticity remains unclear. The goal of this scoping review was to synthesize what is known about how changes in corticospinal transmission and spinal reflex excitability contribute to disrupted ankle control after SCI. We followed published guidelines for conducting a scoping review, appraising studies that contained a measure of corticospinal transmission and/or spinal reflex excitability paired with a measure of VAC and/or spasticity. We examined studies for evidence of a relationship between neurophysiological measures (either corticospinal tract transmission or spinal reflex excitability) with VAC and/or spasticity. Of 1,538 records identified, 17 studies were included in the review. Ten of 17 studies investigated spinal reflex excitability, while 7/17 assessed corticospinal tract transmission. Four of the 10 spinal reflex studies examined VAC, while 9/10 examined ankle spasticity. The corticospinal tract transmission studies examined only VAC. While current evidence suggests there is a relationship between neurophysiological measures and ankle function after SCI, more studies are needed. Understanding the relationship between neurophysiology and ankle function is important for advancing therapeutic outcomes after SCI. Future studies to capture an array of corticospinal, spinal, and functional measures are warranted.

Brain white matter correlates of learning ankle tracking using a wearable device: importance of the superior longitudinal fasciculus II

“…The significant positive training effects on behavioral accuracy of sequential ankle tracking and corresponding brain white matter integrity found in our study provide strong support for the applications of using sensor-based ankle tracking systems in the clinics, particularly for patients with neurological disorders, such as patients with stroke, spinal cord injury, or traumatic brain injury, who often present ankle control problems [ 69 – 76 ]. Training to improve ankle control of these patients is challenging in rehabilitation.…”

Walking and Balance Outcomes Are Improved Following Brief Intensive Locomotor Skill Training but Are Not Augmented by Transcranial Direct Current Stimulation in Persons With Chronic Spinal Cord Injury

“…Increased corticospinal drive ( Schubert et al, 2008 ), earlier onset motor unit activation ( Van Cutsem et al, 1998 ), increased type II muscle fiber recruitment ( Wilson et al, 2012 ), and increased rate of force development ( Del Vecchio et al, 2019 ) are aspects of ballistic training that may support improved forward propulsion kinematics and facilitate walking speed modulation in persons with motor deficits. These features of training may account for the comparable changes in TLA we observed despite the marked differences in training mode and duration; however, the effects of the MST circuit in persons with MISCI may be restricted to the less impaired limb, where greater corticospinal tract preservation may contribute to enhanced ability to modulate lower limb kinematics ( Hope et al, 2020 ). Although evidence in non-injured adults suggests that even small-scale changes in TLA (i.e., Δ = 1.5°) can contribute to as much as 65% of the increase in propulsive force generated during slow to fast walking ( Hsiao et al, 2015 ), it is unclear whether the modest increase in TLA we observed was consequential to increases in walking speed among our participants.…”

Assessment of Dorsiflexion Ability across Tasks in Persons with Subacute SCI after Combined Locomotor Training and Transcutaneous Spinal Stimulation

“…One possibility is that it contributes to improved ankle control [16], thereby allowing for improved foot clearance. In the development of TSS interventions to improve functional outcomes, it is important to understand how it influences both voluntary and involuntary muscle activation and how it may contribute to the ability to achieve adequate dorsiflexion [23].…”