Biomechanics of ankle instability. Part 2: Postural sway-reaction time relationship.

PURPOSE: To test the hypothesis that ankles with functional instability will demonstrate greater single-limb postural sway (PS) than their contralateral stable joint and stable healthy controls and to examine the relationship between single-limb postural sway and muscular reaction time to a simulated ankle sprain mechanism.
METHODS: Nineteen male volunteers with a history of unilateral ankle sprain and functional ankle instability (FAI) and 19 healthy male controls performed 12 single-limb PS tests, 3 on each leg with and without vision. Participants provided informed consent. Postural sway data are reported on the FAI group's unstable (UA) and stable ankles (SA), and the control group's dominant (DA) and nondominant ankles (NDA).
RESULTS: With vision, the UA and SA revealed similar postural control; however, the UA showed greater (P < 0.05) anteroposterior PS than the DA (0.46 cm) and the NDA (0.51 cm). Without vision, the UA showed greater (P < 0.05) medial (2.41 cm) and lateral (2.59 cm) PS than the SA and also showed greater (P < 0.05) medial (2.05 and 2.10 cm, respectively) and lateral (2.28 and 2.26 cm, respectively) than the DA and NDA. The relationship between PS and muscle reaction times, derived from the previous article was calculated. Significant correlations (P < 0.05) were found between the unstable ankle peroneus longus (PL) and peroneus brevis (PB) reaction time and lateral (r = 0.63 and r = 0.81, respectively), medial (r = 0.74 and r = 0.76, respectively), and anterior PS (r = 0.56 and r = 0.55, respectively; P < 0.01).
CONCLUSIONS: Results reveal postural sway deficits in ankles with FAI. They also demonstrate a significant relationship between PL and PB reaction times and postural sway in UA. Individuals who sustain an acute ankle sprain and those with FAI require rehabilitation that improves proprioception, strengthens the evertors and dorsiflexors, and restores peroneal reaction time.