Tibial Base Plate for Total Knee Arthroplasty: Symmetric or Asymmetric?

Background: Ideal positioning and best coverage of the tibial base plate are essential in total knee arthroplasty. There are 2 types of tibial base plates: symmetric and asymmetric. The superiority of one to the other is still controversial. The aim of this study was to compare symmetric and asymmetric tibial base plates for total knee arthroplasty in terms of rotational alignment and coverage.

Methods: The study was conducted on a total of 80 cadaveric tibial bones. Two surgeons were asked to place 20 symmetric (group 1) and 20 asymmetric (group 2) tibial base plates taking care to ensure the best coverage that they were able to determine. Afterwards, the rotational errors and coverage were assessed with reference to the posterior tibial margin and posterior condylar axis on the three-dimensional computed tomography (3D CT) scan. In the second part of the study, the surgeons were asked to place 20 symmetric (group 3) and 20 asymmetric (group 4) base plates taking care to ensure the best rotational alignment. The rotational errors and the areas uncovered or overstuffed after the application were measured on the 3D CT scan.

Results: On the comparison of rotational errors, while there was no significant difference between group 1 and group 2 in terms of coverage ( = 0.624), the mean external rotation error was significantly greater in group 2 ( = 0.034). On the comparison of coverage, while there was no significant difference between group 3 and group 4 in terms of rotation ( = 0.36), the mean ratios of the uncovered tibial surface to the total tibial surface ( = 0.041) and also the overstuffed area to the total base plate surface ( = 0.029) were significantly greater in group 4.

Conclusions: The determination of correct size and rotation of the tibial component is essential for favorable outcomes of total knee arthroplasty. In this study, the symmetric tibial base plate design was more effective than the asymmetric design in providing the ideal tibial rotation and coverage.