Chronic Ankle Instability and Neural Excitability of the Lower Extremity

Abstract

Context: Neuromuscular dysfunction of the leg and thigh musculature, including decreased strength and postural control, is common in patients with chronic ankle instability (CAI). Understanding how CAI affects specific neural pathways may provide valuable information for targeted therapies.Objective: To investigate differences in spinal reflexive and corticospinal excitability of the fibularis longus and vastus medialis between limbs in patients with unilateral CAI and between CAI patients and participants serving as healthy controls.Design: Case-control study. Setting: Research laboratory. Patients or Other Participants: A total of 56 participants volunteered, and complete data for 21 CAI patients (9 men, 12 women; age ¼ 20.81 6 1.63 years, height ¼ 171.57 6 11.44 cm, mass ¼ 68.84 6 11.93 kg) and 24 healthy participants serving as controls (7 men, 17 women; age ¼ 22.54 6 2.92 years, height ¼ 172.35 6 10.85 cm, mass ¼ 69.15 6 12.30 kg) were included in the final analyses. Control participants were matched to CAI patients on sex, age, and limb dominance. We assigned ''involved'' limbs, which corresponded with the involved limbs of the CAI patients, to control participants.Main Outcome Measure(s): Spinal reflexive excitability was assessed via the Hoffmann reflex and normalized to a maximal muscle response. Corticospinal excitability was assessed using transcranial magnetic stimulation. Active motor threshold (AMT) was defined as the lowest transcranial magnetic stimulation intensity required to elicit motor-evoked potentials equal to or greater than 100 lV in 5 of 10 consecutive stimuli. We obtained motor-evoked potentials (MEPs) at percentages ranging from 100% to 140% of AMT.Results: Fibularis longus MEP amplitudes were greater in control participants than in CAI patients bilaterally at 100% AMT (control involved limb: 0.023 6 0.031; CAI involved limb: 0.014 6 0.008; control uninvolved limb: 0.021 6 0.022; CAI uninvolved limb: 0.015 6 0.007; F 1,41 ¼ 4.551, P ¼ .04) and 105% AMT (control involved limb: 0.029 6 0.026; CAI involved limb: 0.021 6 0.009; control uninvolved limb: 0.034 6 0.037; CAI uninvolved limb: 0.023 6 0.013; F 1,35 ¼ 4.782, P ¼ .04). We observed no differences in fibularis longus MEP amplitudes greater than 110% AMT and no differences in vastus medialis corticospinal excitability (P . .05). We noted no differences in the Hoffmann reflex between groups for the vastus medialis (F 1,37 ¼ 0.103, P ¼ .75) or the fibularis longus (F 1,41 ¼ 1.139, P ¼ .29).Conclusions: Fibularis longus corticospinal excitability was greater in control participants than in CAI patients.Key Words: transcranial magnetic stimulation, Hoffmann reflex, lateral ankle sprain Key PointsCorticospinal excitability in the fibularis longus at transcranial magnetic stimulation intensities of 100% and 105% of active motor threshold was higher in the healthy control group bilaterally than in the chronic ankle instability group. Transcranial magnetic stimulation intensities at 110% or more of the active motor threshold did not result ...

Alterations in Cortical Activation Among Individuals With Chronic Ankle Instability During Single-Limb Postural Control

“…7,8 Similarly, Kosik et al 9 reported deviations in cortical mapping and excitability of the fibularis longus with the use of transcranial magnetic stimulation among patients with CAI compared with healthy control participants. These studies [7][8][9] have contributed to the concept of altered neural pathways after ligamentous injury.…”

“…The long-term disability associated with CAI may also demonstrate some of these CNS changes, including altered neural mapping and corticalactivation changes. 7,8 Individuals with CAI demonstrated smaller motor-evoked potentials, as well as deficits in motor thresholds, providing insight into how the descending pathways from the brain activate the ankle's musculature to control movement. 7,8 Similarly, Kosik et al 9 reported deviations in cortical mapping and excitability of the fibularis longus with the use of transcranial magnetic stimulation among patients with CAI compared with healthy control participants.…”

“…7,8 Individuals with CAI demonstrated smaller motor-evoked potentials, as well as deficits in motor thresholds, providing insight into how the descending pathways from the brain activate the ankle's musculature to control movement. 7,8 Similarly, Kosik et al 9 reported deviations in cortical mapping and excitability of the fibularis longus with the use of transcranial magnetic stimulation among patients with CAI compared with healthy control participants. These studies [7][8][9] have contributed to the concept of altered neural pathways after ligamentous injury.…”

Gait Biomechanics in Participants, Six Months after First-time Lateral Ankle Sprain

“…Indeed, ankle sprain injury is likely to be associated with alterations in alpha motor neuron excitability [17] and previous research has shown that CAI participants activate their peroneus longus (PL) prior to HS earlier than non-injured controls [9]. This early activation may coincide with a decrease in the excitability of spinal reflexes of the lower extremity [18,19] and may prevent normal medial displacement of the center of pressure during the stance phase of gait, resulting in individuals with CAI bearing weight more laterally on their foot (and increasing total frontal plane displacement) [9]. Participants with a history of ankle sprain have previously been shown to apply greater loading through the lateral column of their foot during the latter part of stance [23,32].…”

Evaluating and Differentiating Ankle Instability

“…Multiple sensorimotor deficiencies have been observed in patients with a history of LAS, 92 and changes in cortical and spinal pathways among populations with CAI have been documented. [93][94][95][96][97][98][99] These alterations may help to explain many of the disease and patient-reported deficiencies observed during clinical examination but are currently limited to laboratory techniques. It is possible that in the coming years, this emerging body of information may influence the comprehensive assessments of patients with LAS.…”