Alignment techniques in total knee arthroplasty

Total knee arthroplasty (TKA) reduces knee pain to improve knee function for painful knee osteoarthritis and provides excellent long-term survivorship. However, approximately 20% of patients remain dissatisfied. To improve patient satisfaction, several modifications of knee alignment have recently been introduced. The aim of this paper is to review various alignment techniques. Principles, surgical techniques, and clinical results of various alignment techniques for TKA were searched in the PubMed database. Mechanical alignment aims to cut perpendicular to the mechanical axes of the femur and tibia in the coronal plane. The threshold of the deviation from the mechanical axis for long-term survivorship is still unknown. Anatomical alignment aims at neutral alignment but 2–3 varus joint line relative to the mechanical axis. Although catastrophic polyethylene wear was reported in the 1990s, excellent mid-term clinical results were recently reported using surgical robots. Kinematic alignment aims to restore the pre-arthritic native limb alignment and avoid soft tissue release. To avoid excessive alignment deviation, some modification such as inverse kinematic, restricted kinematic, and modified kinematic alignments are also introduced. Equal or better clinical scores have been reported in short term. Functional alignment TKA aims to restore pre-arthritic alignment and achieve balanced soft tissue tension by adjusting bone resections using robotic-assisted technology. Wide range of clinical results exist for new alignment techniques in the short term. The safe range of alignment for long-term survivorship remains unknown. Further high-quality studies should be performed to warrant the widespread use of new alignment techniques.