Increased subtalar rotational motion in patients with symptomatic ankle instability under load and stress conditions

Abstract

Purpose Diferentiating subtalar and ankle instability in the clinical setting is challenging. This study aims to analyze the rotational laxity of the subtalar joint bilaterally in patients with asymptomatic and symptomatic ankle instability under simulated load and stress-induced position of the subtalar joint. Methods A case-control study was conducted using an adjustable load device (ALD). Patients with chronic ankle instability and healthy volunteers were included. Each subject underwent a CT scan under mechanical stress and simulated weightbearing conditions, maintaining maximum eversion and inversion hindfoot positions. The images were obtained in a single model, allowing calculations of the motion vector as well as the helical axis. The helical axis was deined by a rotation angle and a translation distance. Results A total of 72 feet were included in the study. Thirty-one patients with unilateral symptoms and ive healthy controls were selected, deining two groups: symptomatic (n = 31) and asymptomatic (n = 41). An absolute diference of 4.6º (95%CI 2-11.1) rotation angle was found on the helical axis of the symptomatic vs. asymptomatic group (p = 0.001). No signiicant diferences were detected in the translation distance (n.s.) between the groups. Additionally, a signiicant positive correlation was found between the rotation angle and translation distance through the helical axis in the asymptomatic group (r = 0.397, p = 0.027). Conclusion Patients with chronic ankle instability suspected of having subtalar joint instability showed a wider subtalar range of laxity in terms of rotation about the helical axis. Furthermore, diferences in kinematics between symptomatic and asymptomatic hindfeet was demonstrated when both feet were compared. Level of evidence III.