Analysis of ankle-hindfoot stability in patients with ankle instability and normals.

<bold>Purpose: </bold>We devised a testing apparatus for in vivo analysis of ankle stability. The purpose of the study was to test the reliability of this apparatus and to determine the stability pattern of the ankle-hindfoot complex in healthy, asymptomatic volunteers and in patients with ankle instability.<bold>Methods: </bold>Ten healthy individuals were studied, and testing was repeated on the same day and different days. Three patients with symptomatic, unstable ankles were also tested on both involved and uninvolved sides. Constant inversion torque was applied, then internal rotation torque, while moving the ankle throughout the range of sagittal motion. Three-dimensional kinematics of the ankle-hindfoot complex were measured by an electromagnetic tracking system.<bold>Results: </bold>Measurements were repeatable, with intraclass correlation coefficients 0.9 or better. Variability was observed among controls, but motion curve patterns were consistent. Motion curve slopes were sensitive in differentiating between unstable and stable ankles.<bold>Conclusions: </bold>Most previous reports are in vitro studies conducted with the ankle in one position, manual stress applied, or joint positions estimated with planar radiographs. Our study indicated that more accurate diagnosis of severity of ankle ligament injuries may be possible. [ABSTRACT FROM AUTHOR]