The Contribution of Mobile Bearing Knee Design in Optimizing Tibial Rotation in Total Knee Arthroplasty

This study assessed the alignment and rotation in mobile bearing total knee arthroplasty (TKA) with the tibia cut first technique using an imageless referencing computer navigation protocol evaluating 41 patients. Prerelease mechanical alignment (MA) averaged 7° varus +/−5° (Range: 8° valgus to 20° varus). Post implant MA was 0.5° varus +/−1.2° (Range: 2° valgus to 3° varus). Post operative radiographic MA was 0.3° varus +/−1.3° (Range: 2° valgus to 2° varus). The baseline measurement of tibial rotation from 0° to 90° flexion was 6°+/−7.2° of tibial internal rotation (Range: 8° external rotation to 19.5° internal rotation). The post implant tibial rotation from 0° to 90° flexion was 3.6°+/−8° of tibial internal rotation (Range: 17° external rotation to 29° internal rotation). Of the baseline group, 25 % demonstrated tibial external rotation with flexion. After TKA, 28 % had tibial external rotation with flexion. When comparing the nominal tibial position in relation to the femur at 0° before and after TKA, the tibial rotation point at 0° moved more externally in 21 % and more internally in the rest with mean change for the overall group of 3.9° of internal rotation (Range: 17° internal to 5° external). This study identified significant changes in knee rotation that may be caused by correction of alignment and deformity. Mobile bearing implants by nature of unconstrained rotation are likely to accommodate these variations. This feature could be defined as a significant advantage over fixed-bearing prostheses.