Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Collaborative Specialization

Musculoskeletal Health Research

Supervisor

Willing, Ryan

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.

Summary for Lay Audience

Total knee replacement (TKR) is a surgery used to treat severe cases of knee arthritis after all other methods of treatment have been unsuccessful. It involves removing damaged bone and cartilage and replacing them with metal and plastic implants. It is an effective surgery for reducing a patient’s pain and allowing them to move again, but patients aren’t as satisfied after TKR when compared to other joint replacement surgeries. The success of TKR is determined by how the joint moves and how stable it feels during and after surgery. However, the fact that some patients still aren’t satisfied suggests that more sophisticated testing methods are needed before surgery to better understand how these knee implants behave while they’re still being designed. During this earlier design stage, implants are tested on large robotic platforms called joint motion simulators. Some of these platforms, called knee simulators, control a knee’s movements by pulling on surrounding muscles. Other platforms, called robotic knee testing systems (RKTS), control movements by applying forces directly to the knee’s bones or simply telling the robot to move the knee by a certain amount. These three types of joint control are important for measuring how the joint moves in their own way. However, no single platform exists that can move a joint in all three types of control. This thesis describes how we designed, developed, and validated a system that can do exactly that.

Once validated, the new muscle actuator system (MAS) was used to study the effects of muscle forces on joint stability compared to normally used methods of testing joint stability. The effects of muscle forces on tibial TKR implant rotations, which are already known to change how the knee behaves, were also compared against tests that were performed using the force and movement control methods commonly seen in RKTS. These studies all used an artificial knee joint model called a TKR-embedded phantom joint. In the final study of this thesis, muscle-controlled motion of real cadaver knees was compared against force and movement-controlled tests.

The initial validation study demonstrated that the MAS could produce joint behaviour generally matching those produced by a gold-standard knee simulator. Subsequent studies, using either artificial phantoms or cadaveric knees, outlined the differences in joint behaviour between methods of simulator joint control. These observations established the MAS as a single platform capable of completing work that would usually require multiple different systems to complete.

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