A TIBIA FIRST GAP BALANCED PATIENT-SPECIFIC ALIGNMENT TOTAL KNEE ARTHROPLASTY TECHNIQUE ACHIEVES BETTER TKA BALANCE THAN MECHANICAL, KINEMATIC, AND FUNCTIONAL ALIGNMENT

Purpose This study evaluates four different alignment techniques to assess knee TKA balance. Methods A prospective cohort of 1035 patients undergoing primary robotic-cruciate-retaining TKA by a single surgeon were analysed. The Velys TKA robotic system collects a balance curve that enables the surgeon to intra-operatively analyse the balance consequence of a mechanically aligned (MA), kinematically aligned (KA), functionally aligned (FA), and patient-specific aligned (PSA) TKA. FA was determined by starting from the KA position and then making positional implant changes to balance the TKA with equal extension gaps, equal medial gaps, and 3 mm more laxity laterally in flexion. The tibia was then cut robotically, and a ligament tensor was inserted to determine the balance consequence of FA. For PSA, the femoral component position was further adjusted, if necessary to achieve optimal balance. Finally, the femur was resected robotically, and the balance outcome of PSA was assessed in a blinded manner. Balance was determined as ±2 mm from optimal. Results A total of 1035 consecutive patients with a mean age of 67 ± 9 years were included. The proportion of balanced TKAs was 16% for MA, 43% for KA, 35% for FA, and 98% for PSA (P < .05). The proportion of potentially correctable TKAs for MA was 18%, Thus MA balanced TKA 34% of the time With KA, 14% were potentially correctable Thus KA balanced a TKA 57% of the time For FA, the planned pre-resection gaps differed significantly after tibial resection (P < .05), and 19% were potentially correctable. Thus FA balanced a TKA 54% of the time. The factors that showed a significant difference for a unbalanced FA TKA was a greater alignment from neutral p=0.004, a fixed flexion deformity p=0.02 and large posterior osteophytes p=0.04 Conclusion Optimal TKA balance is achieved with a tibia-first, gap-balanced PSA technique