Coronal Alignment: Mechanical Alignment

The basic goal of total knee arthroplasty (TKA) coronal alignment is to achieve a neutral alignment of the lower limb functional axis connecting the hip and ankle centers through the center of the knee joint (Fig. 40.1). The angle between the functional axes of the femur and tibia (i.e., the hip–knee–ankle [HKA] angle) is 0°. This goal can be achieved by aligning implants perpendicular to the functional axes of the femur and tibia, which is called mechanical alignment. Clinical performance deteriorates when the neutral alignment exceeds ±3°; therefore, the goal has been to maintain the results within ±3°. However, recent reports suggest that the results do not deteriorate even when the alignment exceeds ±3° [1], and discussions on the appropriate alignment are ongoing.