Balance assessments for predicting functional ankle instability and stable ankles.

A number of instrumented and non-instrumented measures are used to detect balance deficits associated with functional ankle instability (FAI). Determining outcome measures that detect balance deficits associated with FAI might assist clinicians in identifying impairments that may otherwise go undetected with less responsive balance measures. Thus, our objective was to determine the balance measure that best predicted ankle group membership (FAI or stable ankle). Participants included 17 subjects without a history of ankle sprains (168±9 cm, 66±14 kg, 24±5 yr) and 17 subjects with FAI (172±9 cm, 71±11 kg, 22±3 yr). Balance trials were performed without vision and subjects stood on a single leg as motionless as possible for 20s. Balance was quantified with center-of-pressure measures (velocity, area) and error score. Measures were positively correlated with each other (r range: 0.60-0.76). The multifactorial model with all three measures best predicted group membership (F((3,30))=7.20, P=0.001; R(2)=0.42; percent classified correctly=77%), and was followed by the multifactorial model with resultant center-of-pressure velocity and error score (F((2,31))=8.73, P=0.001; R(2)=0.36; percent classified correctly=74%). The resultant center-of-pressure velocity (F((1,32))=13.46, P=0.001; R(2)=0.30; percent classified correctly=74%; unique variance=12.7%) and error score (F((1,32))=12.51, P=0.001; R(2)=0.28; percent classified correctly=71%; unique variance=12.0%) predicted group membership; however, 95th percentile center-of-pressure area ellipse did not (F((1,32))=4.16, P=0.05; R(2)=0.12; percent classified correctly=65%; unique variance=5.8%). A multifactorial single leg balance assessment is best for predicting group membership. COPV is the best single predictor of group membership, but clinicians may use error score to identify deficits associated with FAI if force plates are not available.