Ankle sprains occur in nearly 50 percent of the population, with close to 70
percent of patients experiencing residual symptoms or recurrent injury. Joint laxity
and neurological function have been proposed to change following ligamentous injury;
however, few studies have investigated these measures concurrently using direct
methodology. As a result, it is unclear if neurological function may no longer be
appropriately tuned to mechanical restraints at the joint among patients with functional
ankle instability. Furthermore it remains unknown what adaptations allow some
patients to “cope” and avoid this neuromechanical decoupling related to instability
after injury. The purpose of this study was, therefore, to evaluate the relationships
between joint laxity & stiffness, and neurological function as measured through
muscle spindle activity, somatosensory cortex activation, corticospinal excitability,
and motoneuronal pool excitability, among subjects with and without functional ankle
instability. The results of this study indicate neuromechanical coupling is a factor
necessary for maintaining joint stability, as evident through associations between
greater joint laxity and higher muscle spindle activity, cortical activation, and greater
tibialis anterior excitability. Relationships were also observed among neurological
factors, where greater corticospinal excitability correlated with higher muscle spindle
activity, but less cortical activation. Our results suggest some neuromechanical
decoupling occurs in patients with functionally unstable ankles because they exhibited xv
greater joint laxity without associated changes in neurophysiologic variables,
indicating the nervous system may have failed to adapt despite altered mechanical
function. Copers, however, demonstrated potential enhancements in coupling, where
cortical excitability was better tuned to the laxity and sensation of the joint, as well as
demonstrating reflexive inhibition throughout joint loading. These findings offer new
insights into the etiology of ankle instability and support treatment of initial injury to
occur on an individualized basis.