Talar neck angle correlates with tibial torsion – Guidance for 3‐D and 2‐D measurements in total ankle replacement

Axial plane alignment of the talar component in total ankle arthroplasty (TAR) is poorly understood and remains a major issue, especially since malpositioning results in increased peak pressure and rotational torque. Further profound knowledge regarding individual anatomy of the talus and its relation to proximal and distal osseous structures is therefore needed. Therefore, 3-dimensional (3-D) surface models of fifty lower extremities were generated using computed tomography (CT) data of patients without ankle osteoarthritis. The talus neck torsion was measured using a novel 3-D measurement method. Then, tibial torsion and subtalar joint axis orientation were measured and correlated to the talus neck torsion. Moreover, a 2-D measurement method of the talus neck torsion was developed. A statistically significant correlation was found between external tibia torsion and medial talus neck torsion, as well as talus neck axis and subtalar joint axis in the transversal and frontal plane. The novel defined 3-D measurement methods indicated excellent interrater and intrarater reliability. The 2-D measurement method of the talus neck torsion was in good agreement with the 3-D method. The results showed that the rotational profiles of the tibia, talus and adjacent joints are interconnected, which should be considered in TAR. Clinical relevance: This study improves the overall understanding of the talar anatomy, as well as its relationship to adjacent osseous structures. The novel 2-D measurement method of the talus neck torsion might improve talar component positioning in the axial plane corresponding to the patient's individual anatomy, and therefore improve survival rate of TAR. This article is protected by copyright. All rights reserved.