Rotational alignment of the tibial component in total knee arthroplasty: the anterior tibial cortex is a reliable landmark

Purpose: to compare the anterior tibial surface curvature, the Akagi’s line and the medial third of the tibial tubercle in order to assess which is the most reliable landmark for correct tibial component rotational positioning in total knee arthroplasty. Methods: three independent investigators reviewed 124 knee MRI scans. The most suitable tibial baseplate tracing for the Nexgen Total Knee System (Zimmer, Warsaw, USA) was superimposed on the scan matching the anterior tibial cortex with the anterior aspect of the baseplate. The rotation of the tibial baseplate tracing was calculated with respect to the transepicondylar axis (TEA), the medial third of the tibial tubercle line, Akagi’s line and the femoral posterior condylar axis (PCA). Customized software was created and used for analysis of the MRI datasets.The reliability of each measurement was then calculated by using the intraclass correlation coefficient for interobserver agreement. Results: observer agreement on the position of the Akagi’s line was within 3° in 64% of the cases and within 5°in 85% of the cases. Agreement on the position of the medial third of the tibial tubercle was within 3°in 29% of the cases and within 5°in 70% of the cases. Agreement on the localization of the anterior tibial surface curvature was within 3°in 89% of the cases and within 5°in 99% of the cases. Component alignment along the anterior cortex guaranteed full matching ± 3° with the epicondylar axis in 75% of the knees. Conclusions: the anterior tibial surface curvature was found to be a more reliable and more easily identifiable landmark for correct tibial component alignment than either Akagi’s line or the medial third of the tibialtubercle. Level of evidence: level III, retrospective cohort study.