Fig. 1 Kinematic model used for the joint coordinate system of Grood and Suntay [ 1 ]. The model is comprised of a chain of three cylindric joints which allow six degree-of-freedom motions. Two rotations (F–E and I–E) and translations (M–L and C–D) occur about and along the body-fixed F–E and I–E ... More

Fig. 2 Body-fixed Cartesian coordinate systems for a right knee for the ISB (gray arrows) and FUNC (dark arrows) joint coordinate systems: ( a ) Femur and ( b ) Tibia. Note that since the origins of the femoral and tibial Cartesian coordinate systems coincide for the ISB, the origin of the tibial ... More

Fig. 3 Process for defining the body-fixed F–E axes for the ISB and FUNC joint coordinate systems (JCS). ( a ) The sagittal plane (gray) was defined as the plane in which the posterior femoral condyles were superimposed. The same transformation to orient the femur in the sagittal plane was applied... More

Fig. 4 Process for defining the 0 deg reference using the femoral and tibial mechanical axes in the sagittal plane. ( a ) The femoral mechanical axis (solid) was the line that extended from the most distal point of the trochlear groove and was rotated 3 deg about that distal point from a line alon... More

Fig. 5 Process for finding the body-fixed I–E axis of the ISB JCS. ( a ) The coronal view (left) was perpendicular to the sagittal plane (far right) and was the view in which the line (dashed) joining the midpoint of the tibia at the joint line to the point at the center of the shaft 10 cm below t... More

Fig. 6 Process for finding the body-fixed I–E axis of the FUNC JCS. ( a ) The axial plane (gray background) was the plane connecting the end points of the major axis of the lateral tibial compartment (black dots) and the point on the medial edge of the tibia (white dot). ( b ) The origin of the ti... More

Fig. 7 Mean rotations as a function of flexion angle for the two joint coordinate systems. Error bars represent ± one standard deviation. The maximum absolute mean V–V rotation was limited to 1.1 deg with the FUNC JCS whereas the mean was 3.9 deg for the ISB JCS which is nonphysiologic. The V–V ro... More

Fig. 8 Mean translations as a function of flexion angle for the two joint coordinate systems. Error bars represent ± one standard deviation. Patterns differed significantly between the ISB JCS and the FUNC JCS for all three translations. Magnitudes of C–D translations generated with the ISB JCS we... More