Introduction

There is no consensus on the choice between a symmetrical or asymmetrical tibial baseplate when performing a TKA. Asymmetrical tibial baseplate designs should provide superior cortical coverage and better rotational alignment than symmetrical baseplates. The objective was to compare the bone coverage and rotational alignment of symmetrical and asymmetrical tibial baseplate through a CT scan analysis.

Methods

This was a cadaveric study including 15 cadaveric knees. Each knee was implanted successively with a symmetrical (SKS, Aston®) and an asymmetrical (SKS EVO Anatomic, Aston®) tibial baseplate. The order of the implantation sequence was random. Implantation was performed on a native knee with preservation of the soft tissues according to the standard surgical technique, under the same conditions as in the operating room. The choice of the size and orientation of the baseplate was determined by seeking maximum bone coverage, without conflict with the soft tissues, and with optimal rotational alignment (Insall’s axis). After each implantation, a CT scan was performed to determine: the overall tibial bone coverage (ratio of implant surface to total bone surface after bone resection), peri-cortical surface covered by the implant (defined areas with 5, 7.5 and 10mm recess from the cortex), rotational alignment (anteroposterior axis passing through the medial edge of the tibial tuberosity and PCL insertion). Statistical analysis was performed using paired knee tests comparing the two baseplate designs.

Results

The overall tibial bone coverage ratio was higher in the asymmetric group (asymmetric: 85.7%, symmetric: 81.7%, p=0.039). The asymmetrical baseplates had a higher peri-cortical surface coverage ratio than the symmetrical baseplates at 5mm (asymmetrical: 63%, symmetrical: 54.6%, p=0.012), 7.5mm (asymmetrical: 70%, symmetrical: 62.8%, p=0.0097) and 10mm from the cortex (asymmetrical: 74.2%, symmetrical: 67.1%, p=0.0013). The symmetrical baseplates were comparatively implanted with more internal rotation than the asymmetrical bases (symmetrical: 10.38°, asymmetrical: 7.1°, p=0.0412).

Conclusion

When performing a TKA, the use of an asymmetrical tibial baseplate maximizes bone coverage while maintaining anatomic tibial rotation. Asymmetrical tibial baseplates have a better ratio of overall tibial and peri-cortical bone coverage and are implanted with less internal rotation than symmetrical bases. With better bone coverage and a rotational alignment closer to that of the extensor system, these results suggest that asymmetric tibial baseplates are more anatomical.