Evaluation of ankle instability using the Biodex Stability System

Ten patients with chronic unilateral functional lateral instability of the ankle were evaluated using the Biodex Stability System. This system uses a multiaxial testing platform which can be set at variable degrees of instability. Patients are then tested for their ability to "balance" the platform during single-limb stance, and a stability index is electronically generated. This stability index is believed to be an objective measurement that correlates with proprioceptive status of the ankle. Instability of the ankle was confirmed in all 10 patients, using stress radiographs. Two levels of platform stability were tested. With the platform in its most stable configuration, there was minimal difference between the previously injured and the uninjured ankle. With the platform set to permit up to 20 degrees of tilt in any plane, 6 of 10 patients had more difficulty balancing the platform with their injured ankle (higher stability index). This preliminary study suggests that the Biodex Stability System may be a useful tool in trying to objectively measure proprioceptive function.