Anatomical references to assess the posterior tibial slope in total knee arthroplasty: a comparison of 5 anatomical axes

There has been no consensus on an ideal anatomical reference to determine the posterior slope of tibia plateau. Posterior slope of the medial tibia plateau was measured with reference to a proposed mechanical axis (MA) and 5 clinically relevant anatomical references in 90 osteoarthritic knees of 66 female patients undergoing total knee arthroplasty. The MA was defined as the line connecting the midpoints of the medial tibia plateau and the tibial plafond, and 5 anatomical references included the anterior cortical line of tibia, anatomical axis of proximal and central tibia, posterior cortical line of proximal tibia, and fibular shaft axis. The average posterior slope was 10.6 degrees with reference to the MA, and the amount of posterior slope varied widely among the patients and depending on the anatomical reference used to measure. This study indicates that the anatomical reference used to measure the posterior slope should be identified in studies where posterior slope is used to evaluate the sagittal alignment of total knee arthroplasty.