Abstract
The objective of this systematic review with meta-analysis was to determine alterations in spinal and corticospinal excitability of ankle muscles in patients with chronic ankle instability (CAI) compared to uninjured controls. Independent researchers performed comprehensive literature searches of electronic databases and included studies that compared groups with and without CAI and investigated neural excitability with Hoffmann reflex (H-reflex) and/or transcranial magnetic stimulation (TMS). A fixed-effect meta-analysis was conducted to determine group differences for (1) soleus and fibularis maximal H-reflex (Hmax)/maximal M-wave (Mmax)-ratios, and (2) soleus and fibularis longus cortical motor thresholds (CMTs). Seventeen studies were included in the current meta-analysis. They showed that the Hmax/Mmax-ratios of the soleus and the fibularis longus in the CAI group were significantly lower than those in the uninjured control group (soleus: d = −0.41, p < 0.001; fibularis longus: d = −0.27, p = 0.04). There was no evidence for changes in the CMT. This systematic review is the first to demonstrate evidence that patients with CAI present decreased spinal reflex excitability in the soleus and fibularis longus. However, there is no evidence of changes in supraspinal excitability when considering only the CMT. The latter result needs to be interpreted with caution as all except one study demonstrate some changes at the supraspinal level with CAI.
Highlights
Chronic ankle instability (CAI) is one of the most prevalent debilitating conditions in athletic populations [1,2]
For maximal H-reflex (Hmax)/maximal M-wave (Mmax) of the fibularis longus, the unipolar stimulating electrode placed over the proximal lateral popliteal fossa to stimulate the posterior tibial nerve with 1 ms squared wave pulse by increasing the stimulus intensity in 1.0 V increments until Mmax plateaued For transcranial magnetic stimulation (TMS) testing, the double-cone coil placed over the contralateral vertex of the cranium relative to the involved limb to deliver a series of magnetic stimuli of 1.0 Tesla
The meta-analysis concluded that the Hmax/Mmax ratio of the soleus was significantly reduced in the CAI group compared to that of the uninjured control group (d = −0.41, 95% CI = −0.62 to −0.19, p < 0.001; see Figure 2)
Summary
Chronic ankle instability (CAI) is one of the most prevalent debilitating conditions in athletic populations [1,2]. The alterations in neural excitability at both spinal and supra-spinal levels suggest that neuroplastic adaptations appear to exist and may contribute to the sensorimotor dysfunction commonly seen in patients with CAI [37]. The purpose of this systematic review with meta-analysis was to determine alterations in spinal and corticospinal excitability of ankle muscles in patients with CAI compared to uninjured controls without a history of ankle sprain. This investigation is critical to providing greater insights into neurophysiological mechanisms underlying sensorimotor control deficits associated with CAI, which will enhance the current understanding of the most prevalent condition in the physically active
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