Kinematics After PS- and CR-Type TKAs

While the promising long-term results of total knee arthroplasty (TKA) have been well-established, satisfaction is only ~70–80%, which is lower than that of total hip arthroplasty (THA), indicating a need for improvements. Cruciate retaining (CR)-type TKA preserves the posterior cruciate ligament (PCL), while posterior stabilized (PS)-type TKA sacrifices both cruciate ligaments and substitutes for PCL function using a post/cam mechanism. There are two primary types of TKA: Fixed-type TKA, in which the polyethylene insert is fixed to the tibial tray, and Mobile-type TKA, in which wear is reduced by the higher conformity between the femoral component and the polyethylene insert, allowing movement with the polyethylene insert on the tibial tray. Furthermore, several models have been developed to reproduce physiological articular surfaces. In contrast, other models are intended to function with a single radius of femoral sagittal plane alignment. However, it is unclear whether they their actual in vivo function matches these concepts. In the 1990s, a method using X-ray fluoroscopy was developed to evaluate in vivo knee kinematics after TKA [1]. The authors reported a shape-matching method to estimate the three-dimensional position of components by superimposing the contours of the components on captured images and computer-aided design (CAD) models [2–4] (Fig. 22.1). We report the in vivo kinematics after CR-type- and PS-type TKA, with a review of the literature.