Kinematic Alignment in Total Knee Arthroplasty: Unresolved Challenges and Barriers to Overcome for Universal Application.

Restoring patient-specific alignment in total knee arthroplasty has emerged as a promising approach to improve joint kinematics and reduce the need for soft-tissue release. Kinematic alignment (KA) and its variants-including restricted, inverse, and functional alignment-seek to replicate the patient's native joint line obliquity (JLO) and pre-arthritic alignment, often guided by classification systems such as the Coronal Plane Alignment of the Knee (CPAK). However, despite the theoretical appeal, the universal adoption of KA remains controversial. This review highlights several concerns, including the risk of early loosening in varus-positioned components, the limited applicability of KA in advanced osteoarthritic knees, the difficulty of applying KA in severe valgus deformity, and the uncertainty in aligning the femoral cylindrical axis with the tibial rotational axis. Moreover, CPAK classification oversimplifies the spectrum of alignment phenotypes, even though JLO exhibits substantial variability in its distribution and its functional significance remains uncertain. Static measurements of JLO may not accurately reflect the dynamic behavior of the joint during gait, especially given compensatory mechanisms in adjacent joints. Evidence also shows poor correlation between 2-dimensional joint line parameters and 3-dimensional joint surface orientation. While restoring native alignment and JLO might remain a worthwhile goal, the limitations of existing classification systems and the paucity of supporting evidence should be acknowledged. KA and its variants offer the potential to restore patient-specific alignment and JLO while minimizing soft-tissue releases, but widespread adoption is limited by unresolved issues such as variability in JLO, unequal CPAK boundaries, and uncertain functional relevance. Until high-quality, long-term studies address these concerns, KA strategies should be applied selectively within safe limits.