Total knee arthroplasty: posterior tibial slope influences the size but not the rotational alignment of the tibial component

摘要

Purpose The reasons leading to rotational tibial malalignment in total knee arthroplasties (TKAs) remain unclear. A previous cadaver study has shown an increase in internal rotation of the anatomical tibial axis (ATA) after the tibial cut. This study investigates the influence of tibial slope on the ATA and the size of the resected tibial surface. Methods CT scans of 20 cadaver knees were orientated in a standardized coordinate system and used to determine the position of the centres of rotation of the medial and lateral tibial articular surfaces and, hence, of the ATA, after a virtual resection of 6 mm with 0 degrees, 3.5 degrees, 7 degrees and 10 degrees slope, respectively. Furthermore, at each slope, the radii of the medial and lateral tibial articular surfaces after resection were calculated. Results Compared to resection of 6 mm with 0 degrees slope, a slope of 3.5 degrees resulted in a mean external rotation of the ATA of 0.9 degrees (SD, 1.5 degrees; P = 0.025). A slope of 7 degrees resulted in a mean external rotation of the ATA of 1.0 degrees (SD 2.0 degrees; P = 0.030) and a slope of 10 degrees had no influence on the rotation of the ATA. The radii of the medial and lateral articular surfaces of the cut tibiae were larger than those of the uncut tibia (P < 0.001). Conclusion Differences in the posterior tibial slope should not contribute to a rotational malalignment when using the ATA to align the prosthetic tibial plateau. Although statistically significant, the change in ATA with increasing slope was negligible.