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The Cardanic or Eulerian description is the most commonly used method for the description of in vivo knee rotation. It is based on the determination of external anatomical landmarks used for the decomposition of the position of the tibia relative to the femur by three rotations about three pre-defined axes. However, the in vivo localisation of external anatomical landmarks is known to be difficult and subjective. Even a small mislocalisation may lead to dramatic consequences: the Cardanic description may become irreproducible and angle values may be overestimated. This error is well documented in the literature and known as the “cross-talk effect”. Therefore this study proposes an additional calibration step of the classic Cardanic description by a reorientation procedure of rotation axes. The procedure is based on biomechanical constraints of knee kinematics as they appear during a knee squat exercise using the …