Characterizing TKR Biomechanics using a Novel Muscle-Driven Joint Motion Simulator
Abstract
Total knee replacement (TKR) is the end-stage treatment for severe cases of knee osteoarthritis (OA). Despite its success in alleviating pain and restoring mobility to the knee, patient satisfaction rates post-TKR are still lower than other common joint replacement surgeries. Knee kinematics and stability, key determinants of successful TKR, are assessed intraoperatively and tracked post-operatively in in vivo clinical studies. However, the persistently low satisfaction rates suggest that more sophisticated pre-clinical testing methods are needed to better understand the biomechanics of these implants early in their development. During pre-clinical testing of TKR implants, different joint motion simulators are used for characterizing the anticipated biomechanics of a reconstructed knee. Some platforms, known as knee simulators, assess the muscle-controlled behaviour of the knee. Others, known as robotic knee testing systems (RKTS), control joint motions through the application of forces or the prescription of displacements directly to the joint itself. All three types of joint control (muscle, force, and displacement) are critical for characterizing the biomechanics of a reconstructed knee joint; however, no single testing platform is capable of all three. This thesis describes the development and validation of a joint motion simulator capable of manipulating a knee in all forms of control.
Once validated, the novel muscle actuator system (MAS) was used to investigate the effects of muscle forces on joint stability compared to conventional methods of laxity testing. The effects of muscle forces on tibial TKR implant component rotations, which are already known to alter joint biomechanics, were also compared against tests conducted in force/displacement joint control. These studies all used a non-cadaveric knee joint model called a TKR-embedded phantom joint. In the final study of this thesis, muscle-controlled motion of post-TKR cadaveric knees was evaluated against force/displacement-controlled motion.
The initial validation study demonstrated that the MAS could produce kinematics and forces generally matching those produced by a gold-standard knee simulator. Subsequent studies, using either non-cadaveric phantoms or cadaveric knees, outlined the differences in joint kinematics between methods of simulator joint control. These analyses established the MAS as a single hybrid platform capable of completing work that would usually require multiple different joint motion simulators.