THREE-DIMENSIONAL KNEE KINEMATICS ANALYSIS AFTER TKA& #12288;& #12288;-DOES THE TILTING OF FEMORAL COMPONENT IN CORONAL PLANE ALWAYS INDICATE “CONDYLAR LIFT-OFF”? -& #12288 ;& #12288;& #12288;& #12288;

Abstract

Single plane 2D-3D image matching procedure using fluoroscopic images with CAD data of components has been a gold standard of the in-vivo knee kinematics analysis after total knee arthroplasty (TKA). Numerous literatures have highlighted the “Condylar lift-off” (CLO) phenomenon that is thought to be the cause of eccentric polyethylene wear. However, these reports have not taken account of the 3D geometry of tibial polyethylene insert (TPI).

We have developed a system for analyzing static 3D relationship between femoral and tibial component after TKA accurately utilizing the biplanar computed radiography. By applying this system to fluoroscopic knee motion analysis, it has been possible to analyze the 3Dbehavior of femoral component on the TPI by reducing the error in determining the out of plane translation and rotation. Four knees underwent TKA and postoperative knee motion analysis. Knee kinematics was analyzed by translation of medial and lateral estimated contact points of femoral component on TPI. CLO was defined as the separation of femoral component from TPI by more than 1 mm.

All 4 knees showed the “tilting” of femoral condyle relativeto tibial base plate in coronal plane (this phenomenon has been generally recognized as CLO) resulted from that one femoral condyle contacted with the lower potion in convex geometry of the TPI while the other contacted with the higher potion. This was occurred by a rotation of femoral condyle. However, no CLO was demonstrated in this series. This might be because that recorded knee motions were relatively slow and supported by examiners.

From the results of this report, it was proved that a tilting of femoral component relative to tibial base plate in coronal plane not always indicates CLO. For detailed analysis of knee kinematics after TKA, it was thought to be necessary to take account of the geometry of TPI.