Contralateral cutaneous reflex modulation during gait in individuals with and without chronic ankle instability.

INTRODUCTION: Chronic ankle instability (CAI), a common seqeula to ankle injury is characterized by a variety of sensorimotor deficits extending beyond the previously injured limb. Cutaneous reflexes have been identified as a potential contributor to these functional limitations with recent studies identifying alterations in reflex patterns following sural nerve stimulation among those with CAI. To date, no studies have measured cutaneous reflexes of the unaffected limb in this population, therefore, the objective of this study was to measure contralateral cutaneous reflexes during gait in individuals with unilateral CAI and healthy controls. METHODS: Muscle activity of 6 lower limb muscles was measured in nineteen participants while receiving random, non-noxious sural nerve stimulations during a walking task. RESULTS: Control reflex patterns were generally well-aligned with previous literature while CAI patterns varied from controls in several muscles throughout the gait cycle. Namely, a lack of lateral gastrocnemius facilitation during late stance and medial gastrocnemius inhibition at midstance. Additionally, a lack of significant BF facilitation throughout contralateral swing was noted. These results indicate reflex alterations extend beyond the affected limb in those with unilateral CAI indicating changes at the spinal level following lateral ankle sprains (LAS). Considering the symptom variability in CAI, the lack of significant reflexes exhibited by the CAI group may be due to increased variability in motor output between subjects or between stimulation trials. CONCLUSIONS: These findings highlight the importance of identifying reflex alterations arising from LAS and subsequently treating these limitations through rehabilitation targeting systemic neural pathways rather than local deficits.

Perceived ankle instability and cutaneous reflex modulation during gait.

Cutaneous reflex modulation during rhythmic ambulation is an important motor control mechanism to help minimize stumbling following an unexpected perturbation. Previous literature found individuals with chronic ankle instability (CAI) experience altered reflex patterns compared to healthy controls. Considering CAI is characterized by intermittent feelings of ankle instability, researchers have speculated that these alterations are related to perceived instability. Our purpose was to determine whether variability and magnitude of cutaneous reflex amplitudes can predict perceived instability levels following sural nerve stimulation during gait. Forty subjects walked while receiving random stimulations and reported their perceived instability. Middle latency reflexes among lower leg muscles were calculated using data derived from surface electromyography. Hierarchical logistical regressions revealed a positive relationship between reflex variability of the peroneus longus and lateral gastrocnemius muscles and perceived instability during midstance. This suggests subjects with consistent reflexes following sural nerve stimulation develop a certain level of perceptual expectation resulting in generally lower feelings of ankle instability, while subjects with more variable motor outputs perceive greater instability at the supraspinal level. Cutaneous reflex variability during stance may be an important objective outcome measure to monitor neuromuscular recovery throughout a rehabilitation or as a potential predictor of future lateral ankle sprains.

The role of sural nerve reflexes during drop-landing in subjects with and without chronic ankle instability.

The purpose of this study was to investigate the functional role of cutaneous reflexes during a single-leg drop-landing task among healthy, neurologically intact adults, and to identify whether individuals with chronic ankle instability (CAI) demonstrate altered reflexes and subsequent ankle kinematics. All subjects were physically active adults and were categorized as control (n = 10, Male = 6, Female = 4) or CAI (n = 9, Male = 4, Female = 5) depending on whether they scored a 0 or ≥ 11 on the Identification of Functional Ankle Instability questionnaire, respectively. Subjects performed 30-40 single-leg drop-landing trials from a platform set to the height of their tibial tuberosity. Muscle activity of four lower leg muscles was collected via surface electromyography, while ankle kinematics were recorded via an electrogoniometer. Non-noxious stimulations were elicited randomly to the ipsilateral sural nerve at two unique phases of the drop-landing task (takeoff and landing). Unstimulated and stimulated trials were used to calculate middle latency reflex amplitudes (80-120 ms) and net ankle kinematics (140-220 ms) post-stimulation. Mixed-factor ANOVAs were used to identify significant reflexes within groups and differences in reflex amplitudes between groups. Unlike the CAI group, the control group experienced significant facilitation of the Peroneus Longus (PL) and inhibition of the Lateral Gastrocnemius (LG) when stimulated at takeoff, resulting in eversion immediately prior to landing. When stimulated at landing, the control group experienced significantly more inhibition of the PL compared to the CAI group (p = 0.019). These results suggest lower neural excitability for individuals with CAI, which may predispose them to recurrent injury during similar functional tasks.