Association of intraoperative medial joint gap laxity in the flexion position with subjective knee instability after fixed-bearing posterior-stabilised total knee arthroplasty

Postoperative subjective knee instability is an important clinical outcome after total knee arthroplasty (TKA), however the association with intraoperative soft tissue balance remains unclear. This study aimed to assess the association between intraoperative soft tissue balance and postoperative subjective knee instability in fixed-bearing posterior-stabilised (PS) TKA. This retrospective case-control study included 457 patients who underwent fixed-bearing PS TKA. Intra-articular distraction force was quantitatively applied to measure the gap parameters (length and angle) during surgery. The intraoperative joint gap parameters and postoperative clinical outcomes between the patients with (n = 90) and without (n = 367) subjective knee instability were compared. The risk factors for subjective postoperative knee instability were analysed using multivariate logistic regression analysis. The patients with subjective knee instability demonstrated a medially wider intra-articular gap angle and worse Knee Society Score 2011 symptoms (18 vs. 21; p