Abnormal knee kinematics caused by mechanical alignment in symmetric bicruciate-retaining total knee arthroplasty are alleviated by kinematic alignment

Background: Bicruciate-retaining total knee arthroplasty (BCR-TKA) was developed to maintain anterior cruciate ligament function and thus reproduce natural knee kinematics postoperatively. Traditional surgical techniques, however, may cause several complications secondary to kinematic conflict and ligament overtension. The objective of this study was to use a computer simulation of symmetric BCR-TKA to evaluate the effects of alternative surgical techniques on knee kinematics and ligaments. Methods: A musadoskeletal computer model of a healthy knee was constructed and was used to simulate a BCR model with mechanical alignment (MA). Five adjusted models were investigated, characterized, respectively, by kinematic alignment (KA), two degrees increased tibial slope, two-millimeter distal setting of the tibial component, and an undersized femoral component with either MA or KA. Results: All models exhibited a normal femoral position against the tibia at knee extension, with no anterior paradoxical motion during mid-flexion. The healthy knee model showed medial pivot motion and rollback. In contrast, the BCR MA model demonstrated abnormal bicondylar rollback with excessive tensions of the lateral collateral ligament and posterior crudate ligament during knee flexion, whereas the undersized femoral model with MA partly reduced both tensions. The OCR KA model retained relatively physiological kinematics and suppressed excessive ligament tensions. However, no adjusted model completely reproduced healthy knee conditions. Conclusions: The OCR MA model showed abnormal biomechanics due to kinematic conflict between the retained ligaments and the replaced joint surface. Surgeons using symmetric BCR-TKA should consider using the KA method to achieve sufficient ligament laxity throughout knee flexion. (C) 2020 Elsevier B.V. All rights reserved.