Evolving Philosophies of Alignment in TKA: From Mechanical Uniformity to Personalised Harmony

Background and Objectives: Mechanical alignment (MA) has long been the gold standard in total knee arthroplasty (TKA), aiming for neutral hip-knee-ankle alignment with proven long-term survivorship. However, up to 20% of patients remain dissatisfied, often due to neglect of individual constitutional limb variation and subsequent soft tissue imbalance. This has driven the development of alternative alignment philosophies. This current concepts review aims to determine the various evolving alignment strategies, elucidate their underlying principles, and demonstrate the available clinical outcomes data. Materials and Methods: This review examines MA and the paradigm shift towards personalized alignment techniques, including Kinematic Alignment (KA), restricted Kinematic Alignment (rKA), inverse Kinematic Alignment (iKA), adjusted mechanical alignment (aMA), and the most recent evolution, Functional Alignment (FA). Results: Kinematic alignment and its derivatives (rKA, iKA) seek to better replicate native joint morphology and tension, often reducing the need for soft tissue releases and improving functional outcomes compared to MA. rKA and iKA introduce protective boundaries to avoid extreme phenotypes and possible instability. FA leverages robotic platforms and integrates these principles with real-time gap balancing, demonstrating promise for consistent, personalized outcomes. Some reports, however, advise caution with adjusted Mechanical Alignment (aMA), particularly those that result in phenotypes such as Coronal Plane Alignment of the Knee (CPAK) VII or VIII, which may increase the risk of revision. Conclusions: The philosophy of TKA has evolved from a uniform mechanical target (MA) to a more nuanced, patient-specific strategy. While promising mid- to long-term outcomes and comparable survival data support the viability of KA and its derivatives, critical needs remain, including standardizing nomenclature (especially for FA) and conducting high-quality comparative trials. Future directions involve leveraging high-volume intraoperative data and Artificial Intelligence (AI) to refine decision-making and further personalize alignment strategies, without compromising long-term implant survivorship.