Modeling and Analysis of the Viscoelastic Response of the Ankle Ligament Complex in Inversion Ankle Sprain

Since inversion ankle sprain (IAS) damages ankle ligaments and induces changes in their viscoelastic properties, evaluating these properties may provide an approach to assess injury. The study purposes were to investigate how the viscoelastic properties of the ankle ligament complex can be used to quantitatively assess IAS, and to investigate the usefulness of the stretched exponential function to analyze the relaxation behavior of the ankle ligament complex. Fifteen participants with unilateral IAS and 15 controls were included. The relaxation behavior of each ankle was measured by an instrumented anterior drawer test, and was then curvefitted by the stretched exponential function. By a modeling approach, both parameters of the function were found to be associated with the viscous response. Statistical analysis was performed to determine differences in these two parameters between sprained and uninjured ankles. It was found that sprained ankles exhibited significantly lower viscous response than uninjured ankles. No significant difference was found among uninjured ankles. In conclusion, by using the viscoelastic properties, sprained ankles were successfully differentiated from uninjured ankles. In clinical application, this method could be a diagnostic tool for quantitative assessment of IAS injury. The stretched exponential function was a useful model to analyze the relaxation behavior.