Two different posterior-stabilized mobile-bearing TKA designs: navigator evaluation of intraoperative kinematic differences

Purpose: The purpose of this study was to compare two types of posterior-stabilized (PS) mobile-bearing (MB) total knee arthroplasties (TKAs). The hypothesis was that no major differences were going to be found among the two TKA designs. Methods: Two cohorts of patients who were divided according to implant design (Cohort A, new design gradually reducing radius PS MB TKA; Cohort B, traditional dual-radius PS MB TKA) were analyzed by means of intraoperative navigation. All operations were guided by a non-image-based navigation system that recorded relative femoral and tibial positions in native and implanted knees during the following kinematic tests: passive range of motion (PROM), varus–valgus stress test at 0° and 30° (VV0, VV30) and anterior/posterior drawer test at 90° of flexion (AP90). Results: There were no significative differences in kinematic tests between the two implants. Cohort A, however, showed a different post-implant trend for VV0 and VV30 that were lower than the pre-implant ones, as expected, while for Cohort B, the trend is opposite. However, the gradually reducing radius prosthesis (Cohort A) showed a trend of improving stability (29% compared to the preoperative status) in mid-flexion (VV30) which the traditional dual-radius design (Cohort B) would not. Moreover, we found no differences among postoperative results of the two TKA designs. Conclusion: Despite design variations, no difference has been found among the prostheses in terms of PROM, rotations and translations. Both design kinematics did not show paradoxical external rotations, but an increase in femoral translation in mid-flexion without affecting the functioning of the prosthesis. Level of evidence: II.