Relationship Between The Akagi's Line And The Transepicondylar Axis Of The Femur In Patients With Larger TT-TG

Purpose:Proper rotational alignment in total knee arthroplasty(TKA)is very important for successful outcomes.We often use transepicondylar axis(TEA)as a reference line in the femoral side.For the tibial,Akagi's Line has been proved as a line perpendicular to TEA and the medial border of the patellar tendon has been frequently used to determine the tibial rotational alignment.However,as TT-TG increases,the lateralized tibial tubercle would change the relationship between the TEA and Akagi's Line of the tibia.This study aims to determine whether the Akagi's Line is actually perpendicular to the TEA and useful for the tibial rotational alignment in patient with larger TT-TG.Methods:We studied computed tomography scans of 120 knees with tibial tuberosity-tibial groove(TT-TG)between 15mm?TT-TG?20 mm(experimental group)and 100 knees with TT-TG?15 mm(control group)who undergoing TKA.The TEA of the femoral and the Akagi's Line were identified using the computed tomography scans,and the angle between the line perpendicular to the TEA and the Akagi's Line(AP angle)was measured.We also did the postoperative merchant view radiograph to evaluate the patellofemoral.Result:The mean angle between the line perpendicular to the projected TEA and the Akagi's Line was-1.45°±2.76°(range,-10°-+4°)in experimental group and+1.20°±2.34°(range,-3°-+7°)in control group.And there was no statistical difference between the two group in the postoperative merchant view radiograph.Conclusion:The Akagi's Line of the tibia was,on average,perpendicular to the transepicondylar axis of the femoral in patients with Larger TT-TG.The Akagi's Line would be useful for setting the tibial component with minimal rotational mismatch.