Figure 1.

Knee analog formed by a coordinate measuring machine (CMM). (a) Three anatomical axes for flexion/extension (FE), internal/external rotation (IE), and abduction/adduction (AA) are labeled at the corresponding rotational joints of the CMM. Two labeled IMUs are mounted to the CMM with T (green) analogous to a thigh-mounted IMU and S (blue) analogous to a shank-mounted IMU. (b) Definitions of three frames of reference for a human knee associated with a shank-mounted IMU (blue) including the shank IMU frame, $F_S$, the shank anatomical frame, $F_{AS}$, and the shank IMU’s world frame, $F_{WS}$. Analogous frames of reference are illustrated for the thigh-mounted IMU (green).