Multi-body optimization with knee joint constraints based on the stiffness matrix

Estimation of joint kinematics using optoelectronic system and skin markers can be performed using a multi-body optimization (MBO) method [1]. With the intent to estimate the bone segments pose, MBO should compensate for the effect of soft tissue artefacts (STA), thanks to a multi-body model made of segments and articulated joints (represented by a set of constraints). When modelling the joints as simple mechanical linkages (hinge or spherical), the accuracy of the model-based kinematics is questionable [2]. Some studies have tried to improve the estimated kinematics by using a more detailed anatomical knowledge to model the joints [3,4]. Instead of a deterministic and non-physiological mechanical linkage, the present study proposes an alternative definition of the joint model thanks to a stiffness matrix introduced in MBO through a penalty-based method.