Isokinetic Testing of Evertor and Invertor Muscles in Patients With Chronic Ankle Instability

Abstract

Ankle sprains are among the most common sport-related injuries and can lead to chronic ankle instability. Impaired sensorimotor function of the ankle musculature is often suggested as a cause. The current study sought to assess and compare the isokinetic performance and electromyographic patterns of evertor and invertor muscles in patients with chronic ankle instability and in a control group. Twelve patients with chronic ankle instability and twelve healthy subjects were included. Isokinetic eccentric and concentric testing at various angular velocities was performed for eversion and inversion movements. The corresponding myoelectric activities of the fibularis longus and tibialis anterior muscles were quantified from surface electromyographic recordings by computing average root mean square values. Patients had lower myoelectric activity of the evertor and invertor muscles than controls did; this difference could account for the eccentric weakness associated with ankle instability. Functional strength ratios revealed a dynamic strength imbalance in unstable ankle patients and that may contribute to recurrent injury. Our findings suggest that rehabilitation programs for unstable ankle patients must be focused on the motor control of eccentric contractions of the ankle evertors and invertors, to boost these muscles’ contribution to ankle stabilization.

Influence of balance surface on ankle stabilizing muscle activity in subjects with chronic ankle instability.

“…(11-14, 21, 22). As CAI has been associated with a decreased function of the peroneus longus muscle (15)(16)(17)(27)(28)(29)(30), rehabilitation exercises should target, in the first place, activation of this ankle-stabilizing muscle. Blackburn et al (13) emphasized considering agonist-antagonist co-activation because of the risk of establishing disproportionate muscle activity gains, since increased muscle activity may not be a positive outcome for every injury scenario.…”

An Updated Model of Chronic Ankle Instability

“…Meta-analy-ses 111,112 have shown consistent eversion concentricstrength deficits in patients with CAI. Deficits have also been reported in concentric inversion 113,114 and plantarflexion 115,116 strength and eccentric eversion, 117,118 inversion, 118,119 plantar-flexion, 120 and dorsiflexion 121 strength.…”

Altered Vertical Ground Reaction Forces in Participants With Chronic Ankle Instability While Running

“…In isokinetic muscle testing, those with CAI had a 24% decrease in eccentric tibialis anterior strength compared with control participants. 23 Theoretically, if the tibialis anterior muscle is unable to control the descent of the foot during initial contact, then the foot will strike with greater magnitude, causing an increased impact peak. A decrease in strength of the tibialis anterior may contribute to the increased impact peaks seen in individuals with CAI.…”