Experimental Joint Biomechanics Research Lab


	Experimental Joint Biomechanics Research Lab
	Knee Simulators


	The Kansas Knee Simulator
		The Dynamic Kansas Knee Simulator (KKS) is a servo-hyraulic testing rig that can apply dynamic loading to a knee joint. Loads are generated at the proximal femur, distal tibia, and quadriceps tendon using 5 hydraulic actuators coupled with a 5-axis controller. A vertical load is applied at the hip to simulate the body weight of the subject. The hip is free is to flex and extend and translate vertically. Vertical rotation, medio-lateral translation, and ankle flexion loads can be applied at the base of the tibia. Additionally, the tibia is free to rotate in varus-vagus. The final actuator is mounted to the femur and attaches directly to the quadriceps tendon proximal to the patella. Each of the axis can be controlled in displacement or load control.
	Typically, the flexion-extension position of the knee is controlled by the quadriceps actuator while the remaining axis are left in load control. This most closely resembles how the human body works during normal activities. Sinusoid load profiles can be generated for each axis. Load profiles for the simulator are created using a dynamic rigid body model in the Adams dyanmic modeling software enviroment. The model uses the geometry of the KKS coupled with known knee loading conditions to optomize the actuator outputs. The actual loads generated at the knee can be measured using the insturmented analog knee, seen to the right.
	The KKS can be used to evaluate the performance of total knee replacment components. The components are cemented to aluminum fixtures and mounted into the simulator. The patella is attached to a kevlar strap that simulates the quadriceps tendon. The medial-lateral position and varus-valgus quadriceps angle of the actuator can be adjusted. Additionally, fixtures allow for the internal-external rotation and varus-valgus alignment of the femoral component. The KKS can simulate walking, cutting, or any variety of loading conditions. The simulator can also perform deep knee bends, flexing the components past 120 degrees of knee flexion. The movement of the knee is recorded using an Optotrak 3020 system. Rigid bodies consiting of infrared emitting diodes are mounted to the femur, tibia and patella. By measuring the motion of the rigid bodies, the kinematics of all three bones can determined in 3-D space.
	With a change of fixtures, the KKS can perform all the same simulations on real tissue. To the right, a canine knee is mounted in the simulator. The geometry of the simulator is compatible with knees of almost any size from mid-sized dogs to large bovine specimens, including human tissue. By determining the kinematics of a natural human knee in the simulator, the changes associated with knee surgeries or injuries can be quantified. Testing in cadaver specimens accounts for the effect of the soft tissue around the knee on it's kinematics. Using this method, studies are underway that evaluate the impact of component mal-alignment on implant behavior.

© Department of Mechanical Engineering	Experimental Joint Biomechanics Research Lab	Page last updated April 2008
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