CR prosthesis or PS prosthesis, which one is closer to the natural rollback of the knee joint? ——A vivo kinematics study using Mako robot-assisted im-based-system measurement

Abstract Background Cruciate-retaining (CR) prosthesis and posterior-substituting (PS) prosthesis are widely used in total knee arthroplasty (TKA). The main discrepancy in kinematics between two designs is that the mechanism of rollback motion during knee flexion is different. In this study, by using image-based robotic assisted system (mako), femoral-tibial contact points of these two types of prostheses during 0°to 140°flexion were recorded to compared with the natural kinematic characteristics of knee joints before TKA, so as to explore which type of prosthesis is close to the natural rollback. Method Twelve patients (15 knees) with MAKO-assisted TKA in our center were included. ①After the registration was completed, the knee joint of the patients was flexed at 0°to 140°(10°increasing, A total of 16 angles, including 45°), the contact point of femur and tibia at each angle was recorded by Mako software; ②After the anterior cruciate ligament(ACL) removed and the posterior cruciate ligament(PCL) retained, the CR model was placed, and the contact point of the femur and tibia at each knee flexion angle was recorded again from 0°to 140 °;③The PCL was removed, and the PS prosthesis was implanted finally. Then the contact position of the femur and tibia at each knee flexion angle from 0°to 140 °was recorded for the third time. Through the above process, we obtained the contact position of the femoral condyle and the tibia during the passive flexion of the knee joint at 16 angles in three conditions (1, the patient with natural knee; 2, the patient with CR prosthesis;3, the patient with PS prosthesis) in order to simulate the rollback of the knee joint and compare the difference of rollback in three groups. Results There was no statistical difference in contact points of the femur and tibia between the CR prosthesis and the natural knee at all 16 flexion angles (P > 0.05). The contact points of the femur and tibia in the PS prosthesis group was close to those of the natural knee at flexion range from 20 ~ 50°(P > 0.05); but at 0 ~ 10°flexion and 60 ~ 140°flexion, there was a statistical difference in contact points of the femur and tibia between the PS prosthesis group and the patient 's natural knee joint(P<0.05). Conclusion By using the intraoperative real-time positioning function of image-based robotic assisted system(Mako)to detect the characteristics of knee joint rollback motion, we found that compared with PS prosthesis, the knee joint rollback of patients using CR prosthesis was closer to the natural state.