Mechanical alignment alternatives: From anatomical to kinematic alignment in total knee arthroplasty

Background: Mechanical alignment (MA) has served as the standard of care in total knee arthroplasty (TKA) for four decades, aiming for a neutral mechanical axis to theoretically optimize implant longevity. Despite technical refinements and the integration of robotic assistance, approximately 20% of patients remain dissatisfied with functional outcomes, prompting an investigation into alternative alignment philosophies that prioritize individual constitutional anatomy.

Objective: This review evaluates the methodology, clinical rationale, and current evidence surrounding five distinct alignment strategies: mechanical, anatomical, adjusted mechanical, kinematic, and restricted kinematic alignment.

Key Points: Traditional MA utilizes systematic bone cuts perpendicular to the mechanical axis, often necessitating soft tissue releases. Anatomical alignment (AA) modifies this by targeting a 3° varus joint line while maintaining a neutral limb axis. Adjusted mechanical alignment (aMA) allows for residual constitutional varus up to 5°. Kinematic alignment (KA) aims to restore pre-arthritic joint surface orientation and laxity without soft tissue release, though concerns persist regarding long-term component fixation in cases of severe tibial varus. Restricted kinematic alignment (rKA) proposes a hybrid approach, utilizing KA principles within a defined "safe zone" (coronal alignment ≤3° and tibial obliquity ≤5°) to avoid extreme outliers.

Conclusion: While MA remains the conventional benchmark, alternative strategies like KA and rKA offer potential improvements in physiological kinematics and patient satisfaction. However, long-term survivorship data for these patient-specific approaches remain limited, and the optimal indications for each philosophy continue to be a subject of clinical debate.