Appropriate transverse rotation of the tibial component is critical to achieving a balance of tibial coverage and proper tibio-femoral kinematics in total knee replacement (TKR), yet no consensus exists on the best anatomic references to determine rotation. Historically, surgeons have aligned the tibial component to the medial third of the tibial tubercle1, but recent literature suggests this may externally rotate the tibial component relative to the femoral epicondylar axis (ECA) and that the medial border of the tubercle is more reliable2. Meanwhile, some TKR components are designed with asymmetry of the tibial tray assuming that maximizing component coverage of the resected tibia will result in proper alignment. The purpose of this study was to determine how different rotational landmarks and natural variation in osteoarthritic patient anatomy may affect asymmetry of the resected tibial plateau. Pre-operative computed-tomography scans were collected from 14,791 TKR patients. The tibia and femur were segmented and anatomic landmarks identified: tibial mechanical axis, medial third and medial border of the tibial tubercle, PCL attachment site, and the surgical ECA of the femur. Virtual surgery was performed with an 8-mm resection (referencing the high side) made perpendicular to the tibial mechanical axis in the frontal plane, with 3° posterior slope, and transversely aligned with three different landmarks: the ECA, the medial border, and medial third of the tubercle. In each of these rotational alignments, the relative asymmetry of the medial and lateral plateaus was calculated (Medial AP/Lateral AP) (Fig. 1).Introduction:
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Optimal alignment and position of implants is an important goal In TKA. Conventional mechanical instruments use the anatomic axis and “average” anatomy to position the femoral component to achieve acceptable mechanical limb alignment. Numerous studies have documented the frequency of TKA outliers (+/− 3 degrees) to be 30% or more. The purpose of this study was to determine the “true” distal femoral valgus angle of the femur. 13,586 CT scans of patients undergoing TKA with patient specific instruments were analyzed. Three-dimensional reconstructions were performed and the distal femoral anatomic and mechanical axes were measured digitally. The distal femoral valgus angle was defined and the difference between the anatomic and mechanical axes of the distal femur.Introduction
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Optimal alignment of the tibial component in TKA is an important consideration. General agreement exists on the appropriate coronal alignment. However there is no consensus on sagittal alignment (posterior slope). Some surgeons target a fixed posterior slope (usually between 0 and 10 degrees), while others attempt to match the patient's intrinsic anatomy. The purpose of this study was to evaluate the tibial posterior slope in patients undergoing TKA. 13,586 CT scans of patients undergoing patient specific were analyzed. Three-dimensional reconstructions were performed and the posterior tibial slope was measured. Mean slope and ranges were determined.Introduction
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