Component alignment in total knee arthroplasty.

Prosthetic component positioning in total knee arthroplasty is a critical determinant of long-term survival of the implant. The goal of component alignment is to recreate the normal mechanical axis of the lower extremity and to achieve a stable, balanced articulation. In addition to component position, it is desirable to select a prosthesis size that, as closely as possible, matches that of the patient. The tibial component is usually placed perpendicular to the longitudinal axis of the tibia in the coronal plane and, depending on implant design, sloped neutral to posteriorly in the sagittal plane. This positioning differs from the normal alignment of the tibial articular surface, which is oriented in slight varus. Because of the change in tibial orientation, the desired femoral component position also differs slightly from the normal anatomic configuration.