Lift-off reduction and patella tracking in Total Knee Arthroplasty (TKA) using a 3D printed patient-specific knee model

Abstract

The patellofemoral joint is greatly influenced by the geometry and position of the femur during knee flexion. After knee replacement surgery, the joint geometry is changed by the surface replacement and its kinematics by the orientation of the cutting planes planned by the surgeon. The technique presented in this study verifies the compatibility of the cutting method during total knee arthroplasty (TKA) with the geometry of the joint and the kinematics of knee flexion. To confirm the benefit of this method, three patient-specific knee models were printed in 3D. All models were made from the patient’s CT data and the patient’s measurement of flexion motion obtained with an infrared stereo camera. The models are operated according to three different techniques: Kinematic Alignment (KA), Measured Resection (MR) with 3 degrees of external rotation and MR with 9 degrees of external rotation. The resulting postoperative knees from the different alignment techniques are compared to the patient’s preoperative knee. The results show that the movement of the patella is modified after surgery on the model. The different alignments also lead to a variation in the behavior of the tibiofemoral joint. Based on these three examples, MR with an external orientation of the prosthesis results in a patellar movement closer to the preoperative movement. The KA method also reproduces the patella movement almost identically, but a lift-off appears at the tibiofemoral joint. The error observed for each cutting method between the pre-and postoperative patella position varies by a maximum of 5 degrees of rotation and 5 mm of translation, showing that the configuration has an overall small impact on the patellar movement. This study of three cases shows the importance of the preparation of the operation and the adjustment of the prosthesis for each specific patient using the 3D printed model.