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Intraoperatively measuring ligamentous constraint and determining optimal component placement during computer-assisted total knee replacement Illsley, Scott Garth

Abstract

The biomechanical goals of total knee replacement surgery are to restore neutral alignment to the lower limb and balance the soft tissues of the knee. Currently, this soft tissue balancing is considered an art; there are few ways to quantify the appropriateness of the soft tissue balancing that a surgeon does. Furthermore, the few existing techniques for quantifying balance are applied after the bone cut is complete, so the state of the soft tissue cannot enter into the surgical planning process. Since problems with soft tissue balancing represent one of the major unsolved problems in knee surgery, there is considerable interest in developing tools to assist with this process In this thesis, I report on the development and preliminary testing of two specific algorithms. The first is an intraoperative method to precisely identify ligament anatomy for use in a kinematic knee model using a computer assisted surgical system. The second is a method to determine the component placement that minimizes ligament strain and laxity throughout the entire range of motion of the knee. Both methods are requirements for a comprehensive surgical advisory system. The ligament identification method proved sufficiently repeatable on porcine specimens to warrant further testing on cadaver specimens. The component placement algorithm was able to determine optimal placement locations accounting for imbalances introduced on a simulated knee model, and was robust to errors introduced when using the ligament measurement routine to obtain model inputs. Further testing on physical knee models is required for validation of the method's ability to determine optimal component placement and predict passive kinematics. I conclude that the two methods presented have the potential to provide the surgeon with accurate quantitative intraoperative information for use in soft-tissue balancing and surgical planning procedures and warrant further investigation.

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