Rotational Alignment Landmarks in Primary Total Knee Arthroplasty

Abstract

Purpose: We hypothesized that the anterior tibial surface curvature is a more reliable landmark for correct tibial component rotational positioning in TKA respect to the 'Akagi' line and the medial third of the tibial tubercle.Methods: Three independent investigators reviewed 124 knee MRI scans, identifying independently the femoral transepicondylar axis (TEA), the femoral posterior condylar axis (PCA), a line connecting the middle of the posterior cruciate ligament and the medial edge of the patellar tendon attachment (Akagi's line), the medial third of the tibial tubercle and the anterior tibial surface curvature. The most appropriate tibial baseplate tracing for the NexGen Total Knee System (Zimmer, Warsaw, USA) was superimposed matching the anterior tibial cortex with its anterior surface. At this point, the rotation of the tibial plate tracing was calculated in respect to the TEA, the medial third of the tibial tubercle line, the Akagi's line and the PCA. Customized software was created and used for analysis of the MRI datasets. Results:The investigators agreed on the localization of the Akagi's line in 64% of the cases within 3° and in 85% of the cases within 5° (minimum -16°, maximum -7°): this landmark might lead to internal rotation of the tibial component. The observers agreed on the localization of the medial third of the tibial tubercle in 29% of the cases within 3° and, in 70% of the cases, within 5° (minimum -4°, maximum +4°): this landmark might lead to external rotation of the tibial component. The investigators agreed on the localization of the anterior tibial surface curvature in 89% of the cases within 3° and in 99% of the cases within 5° (minimum -1°, maximum +4°): component alignment along the anterior cortex guaranteed full matching ±3° to the epicondylar axis in 75% of the knees. Conclusion:Alignment of the tibial component, when based on the anterior tibial surface, was more reliable and easier identifiable than either the Akagi's line or the medial third of the tibial tubercle. Level of evidence:Level 3 (Retrospective cohort study).