Cardan sequence selection influences subtalar and talonavicular joint kinematics

Cardan angle sequences are widely used to describe three-dimensional joint rotations in the foot and ankle, but differences in rotation order can complicate interpretation, especially in joints with multiplanar motion. This study systematically evaluated the influence of Cardan sequence selection on the kinematics of the tibiotalar, talofibular, tibiofibular, subtalar, and talonavicular joints using both in vivo biplane fluoroscopy gait analysis and in vitro passive joint kinematic data from robotic cadaveric simulation. Six Cardan sequences were evaluated to quantify their effects on joint angle profiles and range of motion. Tibiotalar, talofibular, and tibiofibular joint kinematics were largely consistent across Cardan sequences, supporting continued use of the ISB-recommended XYZ sequence (dorsiflexion/plantarflexion followed by inversion/eversion followed by internal/external rotation). Subtalar and talonavicular joint kinematics exhibited substantial sequence-dependent variations in reported joint angles during gait, prescribed tibial external/internal rotation, and prescribed tibial varus/valgus alignment motions. Sequences prioritizing the Y-axis (inversion/eversion) or Z-axis (internal/external rotation) produced the most significant differences relative to the XYZ sequence. Based on joint- and motion-specific sensitivity, we recommend the XYZ sequence for the tibiotalar, talofibular, and tibiofibular joints; YZX, ZXY, or ZYX sequences for prioritizing transverse subtalar joint motion and XYZ or XZY sequences for coronal subtalar joint motion; and XYZ, XZY, or YXZ sequences for sagittal and transverse talonavicular joint motion, with YZX sequence for coronal talonavicular joint motion. These findings highlight the importance of joint-specific rotation sequence selection to improve consistency, reduce crosstalk, and enhance the clinical relevance of foot and ankle kinematic analyses.