Impacts of Robotic Compliance and Bone Bending on Simulated in vivo Knee Kinematics

Robotic testing offers researchers the opportunity to quantify native tissue loads for the structures of the knee joint during activities of daily living. These loads may then be translated into design requirements for future treatments and procedures to combat the early onset of knee degeneration following an injury. However, high knee loads during testing have the potential to deflect a robotic end effector and cause inaccuracies in the applied kinematics. Furthermore, bone bending could also induce kinematic change. This study aimed to quantify the effects of robotic compliance and bone bending on the accuracy of simulated in vivo kinematics in a KUKA KRC210 serial robotic system. Six (6) human cadaver knees were subjected to cyclic human gait motion while 6 DOF forces and torques were recorded at the joint. A Vicon T-Series camera system was used to independently record the applied kinematics. Periods of highest kinematic deviation occurred during instances of low joint loading, suggesting negligible levels of forced deflection for simulations of moderate levels of activity while results of this small study indicate that high physiologic loading poses low risk of deviation from target kinematics, further testing is necessary to confirm.