Fig. 3

Fracture reduction criteria measured on post-operative WBCT 3 months after ankle surgery. a Medial step-off: measured in the coronal plane on the slide with the highest degree of step-off. 3b Posterior step-off: measured in the sagittal plane on the slide with the highest grade of step-off (only included if more than 20% of the articulating surface was affected). 3c Fibular rotation: the deviation of rotation of the fibula relative to the tibia was measured as the angle of a line between the posterior and anterior tibial tubercles, and a line between the anterior and posterior tubercle of fibula. Measurements of 3c, 3d, and 3e were always performed 10 mm (10 slides) proximal from the beginning of the distal tibial articular surface in coronal plane. 3d Fibular anteroposterior translation: fibular translational deviation anteriorly or posteriorly relative to tibia. The anterior or posterior deviation is being measured with a line (light blue) perpendicular to the midpoint (turquoise line) of the anterior and posterior fibular tubercle (red line). The point where the light blue line crosses the line between the anterior and posterior tibial tubercle (green line) relative to the respective midpoint of this (green) line defines the anterior and posterior translational deviation (dark blue line). 3e Tibiofibular widening: the distance between the medial aspect of the cortex of the fibula and the lateral aspect of the cortex of the tibia. This distance was measured at an angle perpendicular to the midpoint between the anterior and posterior tibial tubercle. 3f Joint space narrowing: defined as the difference in joint space at 3 months minus 12 months. Measured in sagittal plane as the distance between the articular surface of talus and tibia at the central line of tibia