CS-TKA

The low-contact stress (LCS) CS design has unique characteristics that control the motion associated with knee joint flexion and extension with a relatively highly constrained geometry of the femur and tibia. The rotational shear forces between the tibial component and tibia that occur in the fixed type component are absorbed by the unrestrained movable tibial insert and tibial component, providing an advantage for both component and the tibia [1, 2]. This system, including the CR type, which has no constraint in the anteroposterior or rotational directions, has produced good long-term clinical outcomes for 40 years [3–9]. Conversely, poor outcomes in short-term follow-up studies have also been reported [10, 11]. We have used this design for more than 30 years, and in addition to observing favorable clinical outcomes [12–15], we have conducted a research to investigate the reasons behind the conflicting outcomes [16–22]. The research identified that this design has a wider “strike zone,” than other designs, enabling compensation for suboptimal surgical techniques. If the femoral component and soft tissue balance are not ideally placed, the coronal geometry (Fig. 55.1a, b) is able to compensate for the suboptimal placement. Similarly, its mobile design compensates for the rotational placement of the tibial component [23, 24] if the malrotation is within 10°. Various anatomical landmarks have been proposed for placing the tibial component, including the Akagi line [25], and many reports have been published on the reliability of these landmarks. However, in some cases, the landmarks shown in preoperative images are difficult to clearly identify during the actual surgery and high interindividual variability can exist. Since surgery is performed manually by humans, achieving a perfect score of 100 points in every surgery is not always possible. We believe that the CS design avoids the occurrence of unacceptable outliers.