Effect of arch supports on ankle-subtalar complex instability: a biomechanical experimental study

Subtalar instability, which may cause persistent symptoms after severe inversion ankle sprains, often involves failure of the interosseous talocalcaneal ligament (ITCL). While several clinicians have reported surgical treatment for this pathology, nonsurgical management policy has not been well considered. Previously, it was proposed that ITCL failure possibly causes looseness of the tarsal arch construction resulting in abnormal ankle-subtalar kinematics occurring with axial forces. In the current study the author hypothesized that arch-support insole functions to improve abnormal joint kinematics in ankle-subtalar complex instability.

Five fresh-frozen cadaver lower extremities with simulated ankle-subtalar complex instability, which was created by combined sectioning of the anterior talofibular ligament (ATFL) and the ITCL, were subjected to a biomechanical experiment. Cyclic axial loading from 9.8 to 668 N was applied with a material testing machine, while three-dimensional angular displacements in both the ankle and subtalar joints were determined with electric goniometers. The specimens were tested before and after inserting an arch-support insole that supports the medial-longitudinal and transverse arches of the foot.

Inserting the insole decreased the maximum ankle internal rotation, from 3.3 degrees +/- 0.9 degrees to 2.3 degrees +/- 0.4 degrees (p = .028), while subtalar rotation was not significantly changed.

The medial longitudinal arch-support insole reduced abnormal ankle internal rotation created by combined sectioning of the ATFL and ITCL, likely due to improved arch configuration stability.