How frequent is rotational mismatch within 0°±10° in kinematically aligned total knee arthroplasty?

Rotational mismatch of the tibial component on the femoral component within 0°±10° is associated with better function after mechanically aligned total knee arthroplasty (TKA). Kinematically aligned TKA has gained interest; however, the percentage of kinematically aligned TKA within 0°±10° is unknown. The authors prospectively followed all patients who underwent TKA for primary osteoarthritis between December 2011 and April 2012 (194 patients, 195 knees). Each underwent kinematically aligned TKA with manual instruments. Aligning the anteroposterior axis of the tibial component parallel to the line that bisects the oval boundary of the lateral tibial condyle set internal/external rotation. Removing bone from the posterior femoral condyles equal in thickness to the femoral component after correction for cartilage wear set internal/external rotation and anteroposterior translation of the femoral component. Rotational mismatch of the tibial component on the femoral component was determined from a computed tomography scan of the knee. Ninety-seven percent of kinematically aligned TKA with fixed-bearing components had a rotational mismatch within 0°±10° (overall range, -11° to 11°). This percentage was higher and the range narrower than the 85% of TKA within 0°±10° and the -14° to 16° range reported for mechanically aligned TKA. The use of manual instruments to kinematically aligned TKA reliably limited rotational mismatch to within 0°±10°, which has been associated with better function.