Impact of intra-operative predictive ligament balance on post-operative balance and patient outcome in TKA: a prospective multicenter study

Introduction: New technologies exist which may assist surgeons to better predict final intra-operative joint balance. Our objectives were to compare the impact of (1) a predictive digital joint tensioning tool on intra-operative joint balance; and (2) joint balance and flexion joint laxity on patient-reported outcomes. Materials and methods: Two-hundred Eighty patients received posterior cruciate ligament sacrificing TKA with ultra-congruent tibial inserts using a robotic-assisted navigation platform. Patients were divided into those in which a Predictive Plan with a digital joint-tensioning device was used (PP) and those in which it was not (NPP), in all cases final post-operative joint gaps were collected immediately before final implantation. Demographics and KOOS were collected pre-operatively. KOOS, complications and satisfaction were collected at 3, 6 and 12 months post-operatively. Optimal balance difference between PP and NPP was defined and compared using area-under-the-curve analysis (AUC). Outcomes were then compared according to the results from the AUC. Results: AUC analysis yielded a balance threshold of 1.5 mm, in which the PP group achieved a higher rate of balance throughout flexion compared to the NPP group: extension: 83 vs 52%; Midflexion: 82 vs 55%; Flexion 89 vs 68%; Flexion to Extension 80 vs 49%; p ≤ 0.003. Higher KOOS scores were observed in knees balanced within 1.5 mm across all sub-scores at various time points, however, differences did not exceed the minimum clinically important difference (MCID). Patients with > 1.5 mm flexion laxity medially or laterally had an increased likelihood of 2.2 (1.1–4.4) and 2.5 (1.3–4.8), respectively, for failing to achieve the Patient Acceptable Symptom State for KOOS Pain at 12 months. Patient satisfaction was high in both the PP and NPP groups (97.4 and 94.7%, respectively). Conclusions: Use of a predictive joint tensioning tool improved the final balance in TKA. Improved outcomes were found in balanced knees; however, this improvement did not achieve the MCID, suggesting further studies may be required to define optimal balance targets. Limiting medial and lateral flexion laxity resulted in an increased likelihood of achieving the Patient Acceptable Symptom State for KOOS Pain.