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ResultsThe two cadaver specimens tested at 55:45 medial:lateral (M:L) force distribution survived the100,000 cycle test, while both cadaver specimens tested at 75:25 M:L force distribution failed.The finite element model generated distinct differences in compressive strain distributionpatterns in the proximal tibia. A threshold of 2000 microstrain was used for fatigue damage inbone under cyclic loading. Both specimens loaded under 75:25 M:L distribution demonstratedsubstantially larger cortical bone volumes in the proximal tibial cortex that were greater thanthis fatigue threshold.Discussion & ConclusionWe validated a finite element model of tibial loading after TKA. Local compressive strainsdirectly correlated with subsidence and failure in cadaver testing. A significantly greatervolume of proximal tibial cortical bone was compressed to a strain greater than the fatiguethreshold in the varus alignment group, indicating an increased risk for fatigue damage. Thismodel is extremely valuable in studying the effect of surgical alignment, loading, and activityon damage to proximal bone. Emerging techniques that customize tibial tray placement to theindividual patient’s pre-arthritic alignment run counter to the traditional recommendations forcoronal alignment to the mechanical axis of the knee. A method that determines the risk ofbone damage in a patient-specific manner can provide the surgeon with a safe range forcomponent alignment and may even be applicable in preoperative planning.Saturday, October 9, 2010, 14:50-15:20Session A22: Tribology and Biomechanics in ArthroplastyLab-in-a-Knee: Simultaneous Measurement of in Vivo Forces andKinematics*Darryl D'Lima - Scripps - La Jolla, USAClifford Colwell Jr. - Scripps - La Jolla, USANikolai Steklov - Scripps - La Jolla, USAShantanu Patil - Scripps - La Jolla, USA*Email: ddlima@gmail.comBackground: While in vivo kinematics and forces in the knee have been studied extensively,these are typically measured during controlled activities conducted in an artificial laboratoryenvironment and often do not reflect the natural day-to-day activities of typical patients. Wehave developed a novel algorithm that together with our electronic tibial component provideunsupervised simultaneous dynamic 3-D kinematics and forces in patients.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]