Rotational Dynamics of the Talus in a Normal Tibiotalar Joint as Shown by Weight-Bearing Computed Tomography

Background: The aim of this study was to investigate the normal anatomy and rotational dynamics of the talus in the tibiotalar joint using weight-bearing cone-beam computed tomography (WBCT). Methods: In a cross-sectional study of thirty-two healthy subjects divided into two age groups (twenty-six to thirty-six years of age and sixty to sixty-four years of age), low-dose WBCT scans of both uninjured ankles were obtained. The rotation of the talus, medial clear space, anterior and posterior widths of the tibiotalar joint, translation of the talus, and talar tilt were measured. The primary outcome measures were intersubject and intrasubject (bilateral) variation of the talar movements between maximal internal and external rotation. The secondary outcome measures were the effect of sex and age on the movements of the talus. Results: When the ankle is rotated, the talus rotates a mean of 10 degrees with no substantial widening of the medial clear space. All of the measured values changed subtly but statistically significantly between maximal internal and maximal external rotation, with mean changes of 10 degrees (standard deviation [SD] = 5.8 degrees) in talar rotation (p = 0.006), 2.0 degrees (SD = 1.5 degrees) in talar tilt (p = 0.0015), -0.2 mm (SD = 0.5 mm) in the medial clear space (p = 0.01), 0.9 mm (SD = 0.8 mm) in the anterior width of the tibiotalar joint (p = 0.003), -0.4 mm (SD = 0.9 mm) in the posterior width of the tibiotalar joint (p = 0.011), and 2.9 mm (SD = 2.2 mm) in translation of the talus (p = 0.002). Intersubject variation was large, but there was very little intrasubject variation in the total rotational range of motion. There were no differences between men and women with regard to any of the measurements. Conclusions: This study provides reference values with which to evaluate the dynamics of the normal tibiotalar joint in order to clarify rotational stability of the ankle mortise. The internal control of the contralateral ankle seems to be a better reference than population-based normal values.