Ligament balancing and alignment

Background: Mechanical alignment (MA) has long been the standard in total knee arthroplasty (TKA), prioritizing long-term implant survival through neutral coronal cuts and ligament releases. Despite achieving high survivorship, 10% to 20% of patients remain dissatisfied due to residual symptoms and unnatural joint perception. This discrepancy has led to the development of personalized alignment philosophies, such as kinematic and functional alignment, which aim to restore native anatomy and kinematics.

Objective: This review aims to redefine the terminology regarding ligament tension and balancing while discussing the clinical implications of prioritizing ligamentous stability over strict bone alignment.

Key Points: Effective TKA implantation requires a distinction between limb alignment (HKA angle) and ligament tension, which involves distraction forces typically ranging from 60 N to 120 N. Native knee kinematics exhibit differential laxity, with the lateral compartment being more compliant than the medial side, particularly in flexion. Research indicates that achieving isometric, rectangular gaps may not replicate physiological motion; instead, maintaining a stable medial pivot with slight lateral laxity (1.5–2.0 mm) in flexion is associated with superior patient-reported outcomes. While personalized techniques like kinematic alignment aim to restore native joint line obliquity, they must remain within safe boundaries (e.g., HKA 174°–183°) to avoid increased risks of aseptic loosening or patellofemoral complications.

Conclusion: Shifting from an alignment-focused to a balance-focused philosophy, facilitated by robotic or navigational tools, allows for precise, patient-specific ligament tensioning. Restoring the pre-arthritic joint line while maintaining controlled ligamentous balance throughout the range of motion is essential for optimizing functional outcomes.