Abstract
In TKA, prosthetic femoral and tibial implants must be symmetrically placed and matched in the mechanical axis and the ligament gaps must be correctly balanced. The collateral ligaments are the key guide, as they arise from the epicondyles of the distal femur, are perpendicular to the AP axis of Whiteside, and are coincident with the transtibial axis of the proximal tibial surface. A perpendicular bisection of the transtibial axis creates the AP axis of the tibia which is coincident in space with the AP axis of Whiteside (Berger). Measured distal femoral resection targets including TEA, AP axis of Whiteside, and 3 degrees external to the posterior condylar axis works because the stout posterior cruciate ligament limits laxity in flexion, allowing for the anatomical variation of these landmarks to be accommodated. The Insall, Ranawat gap balancing methods work to balance the knee in flexion, often matching the results of a measured resection, but guaranteeing a symmetrically balanced flexion gap. Distal femoral internal rotation can result if the medial collateral is over-released, but experience has shown this not to be a problem if the gaps are well balanced. Tibial tray position must be placed coincident with the AP axis of the tibia, which also is coincident with Akagi's line (line from medial margin of patellar tendon to center of the posterior cruciate ligament). The surgeon can make a line from the AP axis of Whiteside to the anterior tibial which matches the AP tibial axis.
