Master of Science in Mechanical Engineering (MSME)
In 2003, 267,000 Americans received total knee replacements prohibiting high impact athletics for the remainder of a patient’s life. A better understanding of the movement and constraint of the knee is necessary to provide more realistic motion of or possibly eliminate the need for joint prosthetics. Fixed Orientation Displacement Workspaces (FODW) can be applied to study the relationship of the passive constraint system and six (6) degree of freedom (DOF) movement of the human knee. A FODW consists of the volume of possible positions the tibia/fibula can occupy relative to a fixed femur without changing the relative orientation of the bones. Theoretical models of the FODW provided a promising snapshot of knee kinematics. A Displacement Workspace Test Station (DWTS) for mapping FODWs was built. An in vitro articular joint completes the loop between a strain gauge-based six (6) axis load cell and a 6 DOF manipulandum mounted to a fixed reference frame. The joint is hand manipulated while a C++ program, Armtalk, operates applications that sample and filter both manipulandum position/orientation and load cell output signals at over 500Hz. Armtalk automatically stores raw data points at 2 Hz or upon a user foot-pedal signal. Forces and moments acting at the joint and its angular orientation are added to each raw data point by algorithms in a spreadsheet. The algorithms select points that represent a particular FODW according to a user specified range of acceptable joint forces and moments and bone orientations. The Cartesian coordinates of individual FODW data points are input into a NURBS-based CAD program for visualization. The DWTS has a 0.2286 mm positional accuracy, a 200 N capacity, and a 0.075 mm/kN compliance. A 2 DOF test checked the Armtalk application and calculated the DWTS angular accuracy to be 0.008°. To calibrate the load cell, moment and force scaling factors of 0.00922 in lb/unit and 0.00554 lb/unit were calculated, respectively. The spreadsheet algorithms successfully reduced data in a 6 DOF test. The CAD program modeled workspaces from 2 and 6 DOF tests with a 1.3 % volumetric accuracy. The apparatus is ready to map FODW of articular joints.
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Guillet, Michael Daly, "Design and test of a Displacement Workspace Mapping Station for articular joints" (2006). LSU Master's Theses. 4027.
Michael C. Murphy