Relationship between posterior tibial slope and rotation on axial alignment in total knee arthroplasty

Abstract

Posterior tibial slope can help to decrease ligament tension during flexion in total knee arthroplasty. External rotation of the tibial component has also been advocated to facilitate patellar tracking. However, combined anteroposterior inclination and rotation can produce a change in axial alignment. A mathematical model was used to determine the relationship between tibial slope and rotation on axial alignment. Posterior slope of 10° and rotation of the tibial cut of 6° changes axial alignment by slightly > 1°. If a sloped tibial cut is internally rotated, slight valgus will occur. If a sloped tibial cut is externally rotated, slight varus will occur. If the tibial cut is sloped posteriorly and the cut or component is rotated, a change in axial alignment of the limb can occur. Malrotation of a sloped tibial cut should be avoided and when rotational position of the prosthesis is determined by inserting trial components, an assessment of limb alignment should be made before implanting the final components.