Malrotation associated with implant alignment technique in total knee arthroplasty

This study documents the malrotation between the femoral and tibial components associated with contemporary alignment techniques that position the tibial component relative to the tubercle, posterior tibial condyles, transtibial axis, and malleoli. The technique that allows the tibial component to float into alignment as the knee is passed through a range of motion and the technique of coupling the tibial component to the femoral component also were assessed. The average external rotation of the tibial component relative to the femoral component associated with each alignment technique is 19 degrees (tibial tubercle), 5 degrees (transtibial axis), 7 degrees (posttibial axis), 3 degrees (malleolar axis), and 14 degrees (range-of-motion technique). The coupled-component technique produced 2 degrees internal rotation. The observed tendency to externally rotate the tibial component relative to the femoral component with most alignment techniques may account for the high incidence of posteromedial polyethylene wear reported in retrieval studies.