Introduction
The implantation of a TKA can significantly alter the native anatomy of the operated patient. To date, there are several philosophies regarding the anatomical goals of TKA implantation in the coronal plane. The classic goal of systematically restoring a neutral mechanical axis of the lower limb is currently being challenged by proponents of kinematic alignment, which is believed to individually restore the native alignment of the surgical patient; The aim of the present study was to analyze the modification of the native coronal alignment of a population of TKA patients according to different alignment goals.
Methods
Five hundred and twenty TKAs were analyzed. The following angles were measured using an image-free navigation system prior to prosthetic implantation: medial femorotibial mechanical angle without constraint and with maximum manual constraint to reduce deformity, medial distal femoral mechanical angle, medial proximal tibial mechanical angle. The native angles were derived from the osteoarthritic knee angles using a validated correction technique. Femoral and tibial angular data before TKA were pooled for the same patient and transformed into categorical data according to the frontal alignment phenotype.
Data after TKA implantation were calculated by simulating five different coronal alignment techniques: mechanical alignment, restricted mechanical alignment, anatomical alignment, kinematic alignment and restricted kinematic alignment. Femoral and tibial angular data after TKA were pooled for the same patient and transformed into categorical data according to the frontal alignment phenotype as before. The overall phenotype, combining both femoral and tibial phenotypes, as well as the femoral and tibial phenotypes individually were compared before and after TKA. The primary endpoint was the binary endpoint of whether or not TKA restored the natural global phenotype. Secondary endpoints were the binary criterion of whether or not the natural femoral phenotype and the natural tibial phenotype were restored by TKA.
Results
The global phenotype was restored significantly differently by the five alignment techniques (figure 1), and there was a significant difference between each of the pairs of techniques, except for the pair mechanical alignment - restricted mechanical alignment. The femoral (figure 2) and tibial (figure 3) phenotypes were restored significantly differently by the five alignment techniques, and there was a significant difference between each pair of techniques for both phenotypes.
Conclusion
Apart from the kinematic alignment technique, the different alignment techniques induce significant changes in the pre-arthrosis anatomy of the TKA patient. The surgeon must be aware of these modifications. The clinical relevance of this alteration remains to be defined.