Articular Contact Kinematics And Related Research For The Knee Before And After A Cruciate Retaining Total Knee Arthroplasty

Purpose:The objective of this study was to compare the in vivo tibiofemoral articular contact kinematics; the correlation between the changes of maximum flexion angle and the changes of related articular contact translation,6degree of freedom (6-DOF) kinematics and length of medial collateral ligaments (MCL) and lateral collateral ligament (LML) of the knees with end-stage medial osteoarthritis (OA), during a weight-bearing single leg lunge activity before and after a posterior cruciate retaining TKA (CR-TKA).Methods:Eleven primary TKA patients (age64±7yrs; height173.5±9.9cm; weight94.4±14.5Kg (mean±standard-deviation);6left and5right knees;8±2.5months after surgery) with advanced knee osteoarthritis were included in this study with IRB approval. Magnetic resonance images of each OA knee were obtained and used to construct a3D computer model of the knee; the femoral TEA axis was created on the native OA knee. The dual fluoroscopic images of each knee were acquired during weight bearing flexion of the knee before and after CR-TKA. The3D MR image-based OA bone models and the3D CAD models of the TKA components were imported into the software and manipulated individually until their projections matched the silhouettes of the corresponding bones and TKA components on the fluoroscopic images. For quantitatively description and comparision, a coordinate system and femoral TEA axis were created on the native OA knee. The tibiofemoral articular contact area was measured as the overlap of the tibiofemoral cartilage surfaces for the OA knees and the penetration of the femoral component into the tibial liner surface for the TKA knees. Their center of the contact area were defined as the contact points. The femoral condylar motion was measured using the TEA positions at medial and lateral compartments and were projected onto the tibial surface. ThesMCL and LCL were all divided into3equal portions:anterior, middle and posterior portions. The shortest3D wrapping path of each ligament portion was measured. Then the tibiofemoral articular contact tracks, the condylar motion, the6-DOF and the length of the sMCL and LCL from full extension to maximum flexion before and after the CR-TKA were measured. The changes of them before and after TKA and their correlation with the changes of the maximal knee flexion were statistically analyzed.Results:Compare to the pre-operative OA knee, the CR-TKA resulted in statistic changed in contact kinematics including the reduced range of articular contact track and condylar motion and their comparative paradoxical anterior translation; the articular contact and condylar motion centers have all shifted to the lateral side. The increases of the maximal flexion angle after TKA was positively correlated with the increase of maximal flexion angle before TKA (R=0.68, P=0.02<0.05) and negatively correlated with the increase of anterior translation (R=-0.82, P=0.01<0.05) and varus (R=-0.66, P=0.03<0.05) of femoral. The changes of maximal flexion angle after TKA was negatively correlated with the changes of the lengths of the anterior portion (R=-0.73, P=0.01<0.05) and middle portion (R=-0.60, P=0.049<0.05) of the sMCL as well as the anterior portion (R=-0.70, P=0.01<0.05) of the LCL at maximal flexion.Conclusions:These altered contact kinematic features in CR-TKA knees may not be optimal for restoration of normal knee function. The increaseing of the relative anterior translation, varus of femoral and the lengths of the anterior portion of sMCL and LCL may statistically influence the increasing of maximal flexion angle after TKA. Thus, the design of polyethylene and the soft tissue balancing, especially at higher knee flexion angles in operation could directly influence the kinematics results of TKA knee. Further studies are needed to determine the influence of the altered in vivo contact kinematics on the longevity of polyethylene liner and long term clinical outcomes of the TKA.