Effect of component rotational alignment on femorotibial rotational alignment in total knee arthroplasty: comparison between mobile and fixed bearing

Abstract

Purpose

“Rotational self-alignment mechanism" was designed for mobile-bearing total knee arthroplasty (MB TKA) to maintain a natural femorotibial rotational alignment independent of component rotational alignment. However, it is clinically unknown if the influence of component rotational alignment on a postoperative anatomical femorotibial rotational angle (FTRA) in MB TKA is eliminated. This study aimed to determine the effect of component rotational alignments on postoperative anatomical FTRA in MB TKA as compared to fixed-bearing TKA (FB TKA).

Methods

This research comprised a total of 161 knees: 54 ​MB TKAs and 107 FB TKAs. In computed tomography, the postoperative FTRA and rotational alignment of tibial and femoral components to anatomical axes were assessed, and the association between the postoperative FTRA and perioperative radiographic data, including component rotational alignments, was examined.

Result

Rotational alignments of both tibial and femoral components did not correlate postoperative FTRA in MB TKA (tibial component: r ​= ​−0.15, p ​= ​0.26, femoral component: r ​= ​0.22, p ​= ​0.10), however, in FB TKA, rotational alignment of tibial component did correlate postoperative FTRA, while that of femoral component did not (tibial component: r ​= ​−0.65, p ​< ​0.01, femoral component: r ​= ​0.17, p ​= ​0.07). In both groups, preoperative FTRA was substantially associated with postoperative FTRA (MB TKA: r ​= ​0.65, p ​< ​0.01, FB TKA: r ​= ​0.33, p ​< ​0.01).

Conclusions

Component rotational alignments did not affect postoperative anatomical rotational femorotibial alignment in MB TKA. Whereas the rotational alignment of the tibial component has a significant impact on the postoperative femorotibial rotational alignment in FB TKA.