Inverse kinematic alignment for total knee arthroplasty: a new concept for personalized alignment

Background: Total knee arthroplasty (TKA) aims for optimal patient satisfaction, yet outcomes remain inconsistent despite advancements in implant design. Traditional mechanical and anatomical alignment strategies have dominated clinical practice for decades but may not account for individual morphological variations.

Objective: This article reviews contemporary alignment philosophies in TKA, with a specific focus on the methodology, surgical principles, and clinical outcomes associated with inverse kinematic alignment (iKA).

Key Points: Mechanical alignment (MA) utilizes perpendicular resections to the mechanical axes to achieve a neutral hip-knee-ankle (HKA) angle, often necessitating soft tissue releases. Kinematic alignment (KA) seeks to restore native anatomy through bone resurfacing, though restricted KA (rKA) is often employed to avoid extreme component orientations. Inverse kinematic alignment (iKA) prioritizes the restoration of native tibial joint line obliquity, targeting a medial proximal tibia angle (MPTA) between 84° and 92°. Subsequent femoral resections are performed using gap-balancing techniques to achieve ligamentous stability without soft tissue release. Postoperative HKA is maintained within 6° varus and 3° valgus. Clinical evidence indicates that iKA achieves higher patient satisfaction and superior Oxford Knee Score (OKS) thresholds compared to MA at 12-month follow-up. Successful implementation requires a far-medial subvastus approach to preserve the soft tissue envelope and an accurate assessment of rotatory stability.

Conclusion: Transitioning from systematic to patient-specific alignment strategies like iKA allows for the preservation of native joint kinematics and soft tissue integrity. Precise execution of these techniques, supported by a thorough understanding of knee anatomy, may enhance functional outcomes and patient-reported success in TKA.