A physical model to quantify error in determining hip joint angles using euler/cardan angles

A physical model simulating the right hip joint was placed in known combinations of 3D rotations. Euler/Cardan angles were used to calculate the 3D rotations from reflective marker data, and different rotation sequences were compared to the physical model. The ‘xyz’ (proximal segment as reference) and ‘zyx’ (distal segment as reference) sequences gave angles most similar to those of the physical model. Absolute deviation varied with the 3D rotation of the model and was large enough to affect interpretation of study results for some combinations of rotations.