Sensitivity analysis of the ankle morphological parameters. Sensitivity of the ankle morphological parameters in response to deviations in the three rotational components away from the standard pose on the M/L radiograph. The ankle model was positioned such that the lateral malleolus was in contact with the image plane with the principal axis passing through the medial malleolus. From the standard pose defined by the coordinate system (X, Y, Z), the ankle model was rotated by 6 degrees at 1-degree intervals in both directions about each of the three anatomical axes to give a perturbed pose as described by the coordinate system (X’, Y’, Z’). As a schematic representation, the landmarks associated with 3D morphological parameters (black: original position of the landmarks; grey: landmark positions after perturbation) are also shown on the 2D image via projection. The distances of the landmarks on 2D image (L: 3D value; l: unperturbed landmark distances; l’: perturbed landmark distances) varied with different rotational perturbations. A similar perturbation approach was also used for analysis of parameters defined on the A/P radiograph.