Research On Assessment Tool And Contribution Factors For Dynamic Postural Stabiliby In Subjects With Functional Ankle Instability

Objective: The purpose of this study was to(1) propose a new assessment tool to evaluate the dynamic postural stability in subjects with functional ankle instability(FAI);(2) determine the diagnostic accuracy of the new assessment tool for identifying the subjects with FAI and compare the diagnostic accuracy among the existing evaluation methods;(3) analyze the functional characteristics of ankle in subjects with FAI and determine the contributing factors to the dynamic postural stability in subjects with FAI;(4) apply the new assessment tool to evaluate the effect of bracing on the dynamic postural stability in subjects with FAI.Methods: Thirty one subjects with unilateral FAI(sixteen males and fifteen females)and thirty one healthy control subjects(sixteen males and fifteen females) completed the anthropometric test, proprioceptive test, isokinetic test, inversion disturbance test and the multi-directional landing task with and without ankle brace. Several mixed design ANOVA were calculated to determined the effect of FAI, landing directions and bracing on the dynamic postural stability. Receiver operating characteristic curves were used to compare the diagnostic accuracy for identifying the subjects with FAI between the new assessment tool and the existing evaluation methods. Several two-way ANOVA were calculated to analyze the functional characteristics of ankle in subjects with FAI. Three separate backward multiple linear regression models were calculated to determine the contributing factors to the dynamic postural stability in subjects with FAI.Results:(1) The time to stabilization(TTS) of subjects with FAI was longer than control group in forward landing task. Only the medial-lateral time to stabilization(MLTTS) of subjects with FAI was longer than control group in lateral landing task.There is no group differences presented in backward landing task.(2) The diagnostic accuracy for identifying the subjects with FAI of forward landing task was the best in the multi-directional landing tasks. The diagnostic accuracy for identifying the subjects with FAI of the modified TTS based on the attenuation of damped vibration(ADV) was the best among the existing evaluation measures.(3) The subjects with FAI displayed larger absolute error of joint position sense and force sense, larger range of inversion/eversion motion and faster maximum of inversion angular velocity than the control group.(4) The inversion active joint position sense, eversion relative peak torque and range of inversion/eversion motion accounted for 58.9% of the variance in anterior-posterior time to stabilization(APTTS)(P < 0.01, Cohen’s f2=1.43). The inversion active joint position sense and eversion relative peak torque accounted for 27% of the variance in MLTTS(P < 0.05, Cohen’s f2=0.37). The inversion active joint position sense, eversion relative peak torque and range of inversion/eversion motion accounted for 69.5% of the variance in vertical time to stabilization(VTTS)(P<0.01,Cohen’s f2=2.28).(5) The females in subjects with FAI displayed shorter TTS in forward landing task with brace than without brace. The males in subjects with FAI displayed shorter MLTTS and VTTS in forward landing task with brace than without brace.Conclusions:(1) The new assessment tool proposed in this study included the forward landing task and the time to stabilization based on the theory of attenuation of damped vibration. It could evaluate the dynamic postural stability in subjects with FAI more effectively than the existing evaluation methods. The new assessment tool could be used to evaluate the effect of prevention, treatment and rehabilitation methods on ankle injury.(2) The inversion active joint position sense, eversion relative peak torque and range of inversion/eversion motion were the main contributing factors to the dynamic postural stability in subjects with FAI. Therefore,rehabilitation strategies should emphasize the ankle proprioception, eversion strength and restriction of the range of inversion/eversion motion to enhance dynamic postural stability in subjects with FAI.