Summary

Better intraoperative soft-tissue balancing could be achieved with Functional Alignment compared to Mechanical Alignment in TKA

Abstract

Introduction

Intraoperative soft-tissue balance can impact on postoperative outcomes in total knee arthroplasty (TKA). Functional alignment (FA) is a newer surgical technique that aims to position the prosthesis with respect to each patient’s specific bony anatomy while adjusting soft tissue balance using robotics. The aims of this study were to evaluate intraoperative soft-tissue release balancing with FA and mechanical alignment (MA) in robotic-assisted TKA and to investigate the effect of soft tissue balancing on post-operative clinical outcomes. We hypothesized that there would be improved intraoperative soft-tissue balance with FA compared to MA.

Method

This prospective, single-centre, single blinded, randomized controlled trial included 241 patients (121 FA and 120 MA). Robotic-assisted TKA using the same single radius implant was performed in both groups. The intraoperative joint gap (JG) was measured medially and laterally in flexion and extension using the distance between components under valgus and varus stress with robotics after implantation. ‘Extension balance’ was defined as the difference between medial and lateral JG in extension and ‘Medial balance’ was defined as the difference medial JG between extension and flexion. The joint was considered well-balanced in extension balance and medial balance within 1-2 mm of equality. Patient satisfaction, Forgotten Knee Joint Scores and Oxford Knee Scores were recorded 1 year postoperatively.

Results

Medial JG in extension was 2.1 ± 1.1 (average ± standard deviation) in FA, 1.8 ± 1.1in MA, and lateral JG in extension was 3.1 ± 1.2 in FA, 3.2 ± 1.4 in MA. Medial JG in flexion was 1.5 ± 0.8 in FA, 1.5 ± 1.5 in MA. Lateral JG in flexion was 4.0 ± 1.9 in FA, 3.7 ± 1.8 in MA. Extension balance was 1.0 ± 1.2 in FA, 1.5 ± 1.5 in MA. FA gained significantly better extension balance (p = 0.01). The proportion of joints considered well-balanced in extension was higher with FA (≤ 1mm, 67.8% vs. 44.2% in MA; 2mm, 93.4% vs. 75.0% in MA ; both p<0.01). Medial balance was similar (­0.6 ± 1.0 in FA, -0.3 ± 1.5 in MA ,p = 0.10). The proportion of joints considered well-balanced medially was higher with FA (≤ 1mm, 82.6% vs. 71.7% in MA; ≤ 2mm, 96.7% vs. 90.8% in MA,p=0.04). Patient-reported outcomes were similar between FA and MA, and between ‘well-balanced’ and ‘unbalanced’ knees in extension balance and medial balance.

Conclusion

Better intraoperative soft-tissue balancing could be achieved with FA compared to MA in TKA, however, post-operative patient-reported outcomes were similar at 1 year follow-up.