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Introduction: Proper rotational alignment of the tibial component is a critical factor affectingthe outcome of TKA. Traditionally, the tibial component is oriented with respect to fixedlandmarks on the tibia without reference to the plane of knee motion. In this study, weexamined differences between rotational axes based on anatomic landmarks and the true axis ofknee motion during a functional activity.Materials and Methods: 24 fresh-frozen lower limb specimens were mounted in a jointsimulator which enable replication of lunging and squatting through application of muscle andbody-weight forces. Kinematic data was collected using a 3D motion analysis system.Computer models of the femur and tibia were generated by CT reconstruction. The motion axisof each knee (TFA) was defined by the 3D path of the femur with respect to the tibia as theknee was flexed from 30 to 90 degrees. The orientation the TFA was compared to 5 differentanatomic axes commonly proposed for alignment of the tibial component.Results: The average alignment error of the 5 different anatomic axes ranged from 0.1° ER to10.7°IR from the true direction of knee flexion. The most accurate indicator of the direction ofmotion was derived by projecting the trans-epicondylar axis of the femur onto the tibial plateau.On average, this axis was externally rotated by 0.1±6.9°. However, values varied over 21.6°. Incomparison, an axis passing through the medial-third of the tibial tubercle from the center ofthe plateau was internally rotated by 0.3°±6.0° (range: 23.9°).Conclusion: This study demonstrates that rotational axes derived from anatomic landmarks onthe proximal tibia provide an estimate of the direction of movement of the femur that is highlyvariable. Constructions based on the epicondylar axis and the medial third of the tibial tubercleare accurate when averaged over large numbers of cases. However, these methods can lead toup to 10 degrees of internal rotation of the tibial component in individual cases.Thursday, October 7, 2010, 7:30-8:20Session B1: Computer Navigation in TKAWhich Steps Do Trainees Find Most Difficult in Performing KneeReplacement?Sabir Ismaily - Institute of Orthopedic Research and Education - Houston, USALindsey Turns - Institute of Orthopedic Research and Education - Houston, USAJonathan Gold - Institute of Orthopedic Research and Education - Houston, USAJerry Alexander - Institute of Orthopedic Research and Education - Houston, USAKenneth Mathis - The Methodist Hospital - Houston, USA*Philip Noble - Institute of Orthopedic Research and Education - Houston, USA*Email: pnoble@bcm.edufile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]