Malalignment: forewarned is forearmed.

Malalignment in total knee arthroplasty (TKA) is a major source of failure. Concern exists as to the acceptable window for overall coronal alignment in TKA. We evaluated the anatomical coronal alignment of 6070 primary TKAs using standard-length knee radiographs. The mean postoperative alignment was 4.8 degrees of valgus, with 1 standard deviation within the mean defining a range of 2.4 degrees to 7.2 degrees of valgus. The revision rate not related to infection for this well-aligned group was 0.5% (3 degrees =0.47%; 4 degrees =0.54%; 5 degrees =0.47%; 6 degrees =0.39%; 7 degrees =0.62%). In comparison, the failure rate for TKAs aligned in relative varus (<2.4 degrees of valgus) was 1.8% (P=.0004) and for those in valgus (>7.2 degrees of valgus) was 1.5% (P=.0027). Kaplan-Meier survival analysis confirmed these findings. The failure rates were statistically higher for the valgus and varus groups, compared to the well-aligned group within 1 standard deviation of the mean. Moreover, varus-aligned knees failed primarily by medial tibial collapse, whereas valgus-aligned knees failed because of ligamentous laxity. Restoring coronal alignment to between 2.4 degrees and 7.2 degrees of anatomical valgus is the most important surgeon-controlled factor in TKA.