Kinematic Alignment Technique for Unicompartmental Knee Arthroplasty

Overview

The kinematic alignment (KA) technique for unicompartmental knee arthroplasty (UKA) has been successfully performed for decades and presents potential clinical benefits. The discussion and videos in this chapter assist the surgeon in understanding how to perform KA UKA with the calipered technique. The first section defines the KA UKA technique; the second section provides the rationale; the third lists the potential benefits of this technique and summarizes the evidence; the final section briefly describes the surgical technique for medial KA UKA. Our objective is to encourage surgeons to use the KA UKA technique because it is a simple, safe method with a more physiologic outcome. It presents multiple potential advantages over the traditional MA technique, and further investigations are needed to better define its clinical impact and the limits for alignment of components.

Definition

See Video 15.1 Discussion on the definition of the kinematic alignment technique for unicompartmental knee arthroplasty.

Traditional techniques for partial or total knee arthroplasty (TKA) recommend positioning components in a systematic orientation, thereby neglecting the anatomic variation of the individual knee. The standard for decades has been to frontally align the components perpendicular to the femoral and tibial mechanical axes, and to produce an identical tibial slope for all patients; this is known as the mechanical alignment (MA) technique for TKA and UKA. Although MA prosthetic knees altered the knee anatomy and physiologic soft tissue balance, the technique was thought to improve the reproducibility of the implantation. Nevertheless, function and perception of these MA prosthetic knees have been disappointing, ^, despite great advancements in implant design and surgical precision. ^, This has led to the development of more personalized and physiologic techniques of implantation, which respect the individual knee anatomy and soft tissue balance, known as kinematic alignment (KA; Fig. 15.1 ). ^,

Similar to the KA TKA, the goal of the KA UKA is to coalign UKA components with the kinematic axes that dictate native motion of the tibia around the femur. ^, Components are therefore aligned parallel and perpendicular to the cylindrical axis and longitudinal tibial axis, respectively ( Fig. 15.2 ). In simplistic terms, the KA technique for UKA aims to produce a “true resurfacing,” restoring the native joint line level and orientation in the implanted knee compartment ( Fig. 15.3 ). In the case of medial UKA, the individual medial and posterior slopes of the medial tibia plateau and the frontal and axial orientation of the medial femoral condyle are therefore restored ( Fig. 15.3 ). The KA technique for UKA was popularized decades ago under the name ‘Cartier Angle’ technique. ^, Philippe Cartier developed this technique in the 1970s and was influenced by works from Christophe Levigne and Michel Bonnin (Lyon School), who first described the proximal tibia metaphyseal-epiphyseal axis.

The KA and MA techniques differ at almost every step of the procedure (see the Surgical Technique section further in this chapter), with different goals for aligning UKA components. It is therefore important when assessing UKA component performance to consider the technique of alignment by distinguishing between KA and MA positioning of components ( Fig. 15.4 ). The terminology describing the alignment technique is derived from the reference landmark used to align UKA components: the KA and MA techniques respectively align the UKA components on the kinematic axes of the knee and the mechanical axis of long bones ( Figs. 15.4 and 15.5 ).