The relative rigid body motions between the femur and the tibia (termed tibiofemoral kinematics) during flexion activities can provide an objective measure of knee function. Physiologic tibiofemoral kinematics are defined as the six relative rigid body motions expressed in a joint coordinate system where the motions about and along the axes conform to clinical definitions and are free from kinematic crosstalk errors. To obtain physiologic tibiofemoral kinematics, coordinate systems must meet certain requirements which neither have been explicitly stated nor in fact satisfied in any previous publication known to the author. Starting with the joint coordinate system of Grood and Suntay (Grood and Suntay, 1983) where motions conform to clinical definitions, the body-fixed axes must correspond to the functional (i.e. actual) axes in flexion-extension and internal-external axial rotation and both functional axes must be body-fixed throughout knee flexion to avoid kinematic crosstalk errors in rotations. To avoid kinematic crosstalk errors in translations, the origins of the femoral and tibial Cartesian coordinate systems, which serve as stepping stones for computing translations, must lie on the body-fixed functional axes. Neither the paper by Grood and Suntay nor the ISB recommendation (Wu et al., 2002) which adopted the joint coordinate system of Grood and Suntay explains these requirements. Indeed meeting these requirements conflicts with the ISB recommendation thus indicating the need for revision to this recommendation. Future studies where physiologic tibiofemoral kinematics are of interest should be guided by the requirements described herein.

屈曲活动期间股骨和胫骨之间的相对刚体运动（称为胫股运动学）可以提供膝盖功能的客观测量。股骨生理学运动学定义为在关节坐标系中表示的六个相对刚体运动，其中围绕轴和沿轴的运动符合临床定义，并且没有运动串扰误差。为了获得生理性的股骨运动学，坐标系统必须满足某些要求，既未明确声明，也未在作者已知的任何以前的出版物中实际上得到满足。从Grood和Suntay的联合坐标系（Grood和Suntay，1983）开始，其中运动符合临床定义，因此身体固定轴必须与功能轴（即 （实际）轴在屈伸和内外旋转中，并且两个功能轴必须在整个膝盖屈曲过程中固定在身体上，以避免旋转中的运动学串扰错误。为了避免翻译中的运动学串扰错误，用作计算翻译的垫脚石的股和胫骨笛卡尔坐标系的原点必须位于人体固定的功能轴上。Grood和Suntay的论文或采用Grood和Suntay联合坐标系的ISB建议（Wu等，2002）都没有解释这些要求。实际上，满足这些要求与ISB建议存在冲突，因此表明需要对该建议进行修订。感兴趣的生理性股胫运动学的未来研究应以本文所述的要求为指导。