The Effect of Surgical Alignment and Soft Tissue Constraints on the Kinematics, Contact Pressure and Wear of a Total Knee Replacement

As life expectancy and activity levels increase so does demand on total knee replacements (TKRs). Previous studies have determined that poor alignment can result in pain, lower knee scores or increased wear. However alignment alone may not result in early failure. Instead it may be the combination of alignment and the soft tissue conditions within the knee that are important. The aim of this study was to investigate the effect of the soft tissues and surgical alignment on the kinematics and wear of a fixed bearing TKR. Experimental and computational studies were carried out under soft tissue and alignment conditions to reflect the range found in vivo. Previous studies have investigated the effect of soft tissues within the knee and the effect of component alignment as individual variables but not in combination. The higher tension soft tissue conditions resulted in lower displacements and significantly lower wear. Surgical alignment also had a significant effect on the kinematics; a 10° posterior tibial slope dislocated under lower tension constraints. Rotational mismatch resulted in significantly higher tibial rotation and abduction-adduction displacements, which can lead to knee pain and instability. The tibial slope and rotational mismatch alignment conditions resulted in significantly higher wear rates than mechanical alignment or 4° varus joint line. Rotational mismatch should be kept within 4°, the tibial slope should be lower than 4° and the angle between components in the coronal plane should be restricted under kinematic alignment to reduce the rotations and wear. In conclusion, surgical alignment and soft tissue tensions significantly affected the kinematics and wear in this study. One limitation is that the effect of these conditions on patient satisfaction is unknown. Further investigations should be carried out to determine adverse biomechanical conditions in different TKR designs.