Current concept of kinematic alignment total knee arthroplasty and its derivatives

Abstract

The kinematic alignment (KA) approach to total knee arthroplasty (TKA) has recently increased in popularity. Accordingly, a number of derivatives have arisen and have caused confusion. Clarification is therefore needed for a better understanding of KA-TKA. Calipered (or true, pure) KA is performed by cutting the bone parallel to the articular surface, compensating for cartilage wear. In soft-tissue respecting KA , the tibial cutting surface is decided parallel to the femoral cutting surface (or trial component) with in-line traction. These approaches are categorized as unrestricted KA because there is no consideration of leg alignment or component orientation. Restricted KA is an approach where the periarthritic joint surface is replicated within a safe range, due to concerns about extreme alignments that have been considered ‘alignment outliers’ in the neutral mechanical alignment approach. More recently, functional alignment and inverse kinematic alignment have been advocated, where bone cuts are made following intraoperative planning, using intraoperative measurements acquired with computer assistance to fulfill good coordination of soft-tissue balance and alignment. The KA-TKA approach aims to restore the patients’ own harmony of three knee elements (morphology, soft-tissue balance, and alignment) and eventually the patients’ own kinematics. The respective approaches start from different points corresponding to one of the elements, yet each aim for the same goal, although the existing implants and techniques have not yet perfectly fulfilled that goal.

Large multiplanar changes to native alignment have no apparent impact on clinical outcomes following total knee arthroplasty

“…KA posits that better outcomes are brought about by recreation of the native anatomy [24]. Our findings do not support this claim, as those with postoperative alignment parameters closest to the native anatomy (a "surrogate" measure of KA) did not demonstrate better KOOS Pain scores, and moreover those with the greatest deviation from the native anatomy did not have worse ones.…”

“…We therefore did not measure the sagittal plane preoperatively and have detailed our rationale in the methods. The mean values for tibial component slope and femoral component flexion in our cohort are in line with widely accepted practice [24,39]. As they are descriptive integrators of alignment variables, we used the Functional Knee Phenotypes (FKP) and CPAK systems to classify our cohort, both of which have been validated by studies using CT imaging [40][41][42].…”

Clinical and Radiographic Outcomes of Inversed Restricted Kinematic Alignment Total Knee Arthroplasty by Asia Specific (Huang’s) Phenotypes, a Prospective Pilot Study

“…The purpose of TKA is restoring the native harmony of the knee. Three interdependent elements, including morphology, soft-tissue balance, and alignment, should be considered at the same time to reach this goal [ 29 , 30 ]. As shown in Figure 4 , MA, which solely focuses on alignment and ignores the other two elements, has a high ratio of dissatisfaction.…”

“…Among these alignment philosophies, KA and its derivatives try to minimize the change in the soft-tissue balance. Additionally, irKA is not only a soft-tissue respecting strategy, but also provides a chance for intraoperative adjustment [ 29 ]. In our study, the HKAA cut-off value was determined from WOMAC and FJS-12 in the knee of Asian-specific (Huang’s) phenotypes.…”

Postoperative clinical outcomes for kinematically, restricted kinematically, or mechanically aligned total knee arthroplasty: a systematic review and network meta-analysis of randomized controlled trials

“…As a result of restoring the knee to the patient’s native alignment, good soft tissue balance and similarity to the native kinematics are expected to be restored [ 6 ].…”