3D fluoroscopic measuring technique provides knee kinematics with an accuracy of approximately 1 degree for rotations and 1mm for translations [15]. (See Figure 4)
Mobile Bearing Knees
(LCS meniscal bearing)
Cruciate intact medial unicondylar knees exhibit small medial condylar translations similar to ACL intact healthy knees [16].
ACL deficient medial unicondylar knees exhibit paradoxical condylar translations; the femur moves anterior with flexion [2, 3, 4, 16].
PCL retaining TKR exhibits anterior sliding of both condyles with knee flexion with the medial translations much larger than lateral translations (i.e., lateral pivot) [16].
In all cases femur externally rotates with flexion, giving normal range of axial rotations [16].
Non-Congruent Symmetric PCL Retaining Knees
Exhibit paradoxical translations, similar to mobile bearing TKR. Both condyles slide anterior with flexion, medial condyle more than lateral condyle (i.e., lateral pivot) [5, 14]. (See Figure 5)
Femur externally rotates with flexion, providing normal range of axial rotations.
Congruent Symmetric PCL Retaining Knees
Exhibit similar patterns of motion as non-congruent designs, but reduced magnitude of condylar sliding AND axial rotations [6, 17, 18].
Fig. 4. By aligning projections of implant surface models with component outlines in digitized fluoroscopic images, it is possible to precisely determine the 3D motions of the knee replacements [15].
Fig. 5. Non-congruent PCL retaining knee replacements exhibit exaggerated paradoxical translations, where both condyles move anterior with flexion, medial condyle more than lateral condyle [5, 14].