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. 2023 Jan 3;31(4):1483–1490. doi: 10.1007/s00167-022-07302-x

Fig. 1.

Fig. 1

Definition of coordinate system—3D model of the right knee joint; left a: implementation of the x-axis (medial–lateral), “best fit” cylinder of the femoral epicondyles with the transepicondylar centre vector as best approximation of the knee’s flexion axis [17, 22]; middle b: implementation of the z-axis (longitudinal): intersecting plane between x-axis and the FHC as best approximation of the MFA; right c: implementation of the y-axis (anterior–posterior): recrossing the x- and z-axes incorporating the FNP → best approximation of the centre of the knee [5, 18]