Fig. 2

TKA tibia component rotation measures. A Beger’s tibial angle (BTA) formed between the line that connects the geometric centre of the tibial plateau and the tip of the tibial tubercle and the anteroposterior tibial component axis. The geometric centre of the tibial plateau measured in the first CT slice just under the metal tray (A-1) was located and axially transposed to CT slice at the level of the tibial tubercle (A-3). Then, the geometric centre of the tibial plateau and the tip of the tibial tubercle are connected (A-3). The anteroposterior tibial component axis is drowned in a single axial scan through the tibial component perpendicular to the posterior tibial component axis (A-2) and transposed to the CT slice at the level of the tibial tubercle. The posterior tibial component axis was a line tangential to the posterior TKA tibial plateau. The tip of the tibial tubercle is 18° (± 2.6°) externally rotated from the native tibial articular surface, the tibial component was considered neutral (0°) when internally rotated 18° in relation to the tip of the tibial tuberosity. B Anatomic tibial angle (ATA) formed between the anatomic tibial axis (B-1) and the posterior tibial component axis (B-2). The anatomic tibial axis is the line defined by the geometric centre of the lateral tibial plateau and the geometric centre of medial tibial plateau measured in the first tibial CT slice just under the TKA tibial component (B-1). C Bimalleolar posterior tibial component angle (BM_PTCA) is the angle formed by the transmalleolar axis (C-1) between the centre of the medial malleolus and the centre of the fibula in an axial slice situated at the ankle centre and bisecting the malleoli and the posterior tibial component axis (C-2)