Implant geometry is a significant factor in determining knee stability and patient satisfaction following total knee replacement (TKR). Ineffective muscle recruitment, impaired joint functionality and increased implant wear are consequences of an unstable knee replacement. Current knee laxity evaluation techniques are limited in their ability to account for the muscular response to knee instability. This study utilizes a subjectspecific lower-body musculoskeletal finite element (FE) model with dynamic muscle loading to evaluate implant laxity during activities of daily living. The effect of varying implant conformity on the muscle forces required to maintain a target kinematic profile during simulated laxity testing were quantified here for the first time. With increasing implant conformity, muscle force requirements to maintain target kinematics were significantly reduced-on average, as implant conformity increased by 0.1, muscle force requirements were reduced by 10.4%. As expected, contact mechanics of the tibiofemoral joint was also altered with implant conformity-increased conformity resulted in higher contact area and lower contact pressure. The strength of correlation between muscle force and implant conformity was shown to be activity-dependent, with more demanding activities showing a stronger correlation between muscle force and implant conformity. This is a unique and, we believe, insightful approach to assessing the effect of implant geometry on musculoskeletal demands and may have significant and sustained impact on prescribed treatment options for knee osteoarthritis. vii TABLE OF CONTENTS THE EFFECT OF IMPLANT CONFORMITY ON MUSCLE FORCE REQUIREMENTS IN THE IMPLANTED KNEE .