INTRODUCTION: This video concerning total knee arthroplasty (TKA): 1) justifies the importance of restoring the natural joint lines in TKA, 2) shows the concept of creating equal laxities at 0 and 90 degrees of flexion to balance a TKA has little support, 3) presents the surgical technique for kinematically aligning (KA) a TKA that restores natural joint lines and knee laxities, and 4) reviews a Level I study that showed KA TKA provides higher satisfaction than mechanically aligned (MA) TKA.DISCUSSION: The importance of restoring the natural joint lines in TKA is based on the rationale of restoring the three kinematic axes of the knee that are parallel or perpendicular to the natural distal and posterior joint line of the femur. Changing the natural joint lines causes uncorrectable instabilities when performing a TKA (Gu, JBJS, 2014). It is widely assumed there should be equal laxity at 0 and 90 degrees in a well-balanced TKA; however, there is little direct evidence to support this concept (Sikorski, BJJ, 2008). A cadaveric study showed the normal knee has 5x to 3x more varus and valgus laxity, 3x more internal and external laxity, and 5x more distraction laxity at 90 than at 0 degrees of flexion (Roth, ORS, 2014). These data suggest that achieving equal laxities at 0 and 90 degrees of flexion in a TKA is undesirable because these five laxities are over-constrained in flexion. A surgical technique for KA TKA that restores the natural joint lines and knee laxities is presented. The cruciate retaining femoral component restores the natural joint lines when the distal and posterior femoral resections equal the thickness of the femoral component after correcting for cartilage wear (typically 2mm) and the kerf of the blade (typically 1 mm) (Nam, KSSTA, 2014). The tibial component restores the natural joint line when the varus and valgus and anterior and posterior slopes of the tibial resection aligns the limb with no varus and valgus laxity in full extension, and the natural A/P offset of the anterior tibia from the distal femur is restored at 90 degrees of flexion (Howell, KSSTA, 2013).RESULTS: A Level 1 randomized controlled trial of KA and MA TKA showed that the odds ratio of having a pain free knee at two years with the KA TKA (Oxford and WOMAC pain scores) was 3.2 (p=0.020) and 4.9 (p=0.001) respectively, compared with MA TKA. The use of a KA TKA provided better pain relief and restored better function and range of movement compared to the MA TKA (Dossett, BJJ, 2014).