Abstract
Aims
Recently, total knee arthroplasty (TKA) has been generalized as an operation that achieves excellent clinical results. However, younger and Asian patients require even greater implant longevity and functional performance. We hypothesized a novel posterior cruciate-retaining TKA design that restores the anatomical jointline in both sagittal and coronal planes, maintains the femoral posterior condylar offset, and provides low contact stress would provide enhanced patient function with the potential for greater implant longevity.
Methods
The novel TKA design was created based on geometry determined from anatomic specimens, 3-degree step of femorotibial jointline was incorporated in the TKA design for Asian. The novel TKA has an asymmetrical design between the medial and lateral femoral condyle, the medial femoral condyle designed to be 3 degrees larger than the lateral femoral condyle. It refined using finite element analyses (FEA) to minimize peak contact stresses. The alignment evaluation after TKA was performed using using bidirectional CR and CT images. Femorotibial-angle (FTA), the position of the femoral component relative to the 3D mechanical axis, and the rotational alignment of the femoral component relative to the PC line were evaluated before and after TKA to identify changes in the femoral condylar shape. The kinematic evaluation after TKA was performed using a 3D-to-2D model registration technique. Single-plane fluoroscopic imaging was used to record and quantify the motions of knees during a stair-step activity. The contact points between the tibiofemoral motions and the tibial rotational angle were evaluated.
Results
FEA showed peak von Mises stress of 10.5 MPa under 2000 N load, well below the plastic limit of UHMWPe. Changes in the femoral condylar shape after TKA were small based on alignment analysis of the medial and lateral condyles. Kinematic analysis revealed an average 16.9 degrees tibial internal rotation with flexion to 90 degrees. Condylar translations exhibited a medial pivot pattern from 0 to 90 degrees of flexion, with an average of 0.9 mm anterior translation of the medial condyle and 9.0 mm posterior translation of the lateral condyle. As a result, tibial internal rotation with medial pivot pattern was accepted.
Conclusions
The novel TKA design based on restoration of articular surface orientation and bony geometry exhibits in vivo kinematics and alignment, contact mechanics that are compatible with excellent functional performance and implant longevity for Asian.
