Medial Laxity Leads to Inferior Postoperative Clinical Outcomes and Function in Total Knee Arthroplasty.

Background: Achieving proper soft-tissue balance is essential for improving total knee arthroplasty outcomes. This multicenter study aimed to analyze the effects of the gap angle and medial and lateral component gaps on clinical outcomes.

Methods: This retrospective multicenter cohort study was conducted on 656 knees in 11 centers. A tensor device was used to measure the joint gap and varus-valgus angle of the joint gap, and medial and lateral component gaps were determined by subtracting the polyethylene thickness. Correlations between the gap angle, component gap, and clinical outcomes using the Knee Society Score (KSS) and the new Knee Society Score (2011 KSS) were analyzed.

Results: The varus gap angle in flexion positively correlated with the KSS knee score (r = 0.118, P = 0.0183), KSS function score (r = 0.164, P = 0.0009), 2011 KSS symptoms (r = 0.148, P = 0.0030), and 2011 KSS functional activities (r = 0.129, P = 0.0099). The medial component gap in extension negatively correlated with the KSS function score (r = -0.113, P = 0.0241) and that in flexion negatively correlated with the 2011 KSS symptoms (r = -0.127, P = 0.0078) and the 2011 KSS patient satisfaction score (r = -0.119, P = 0.0126). The lateral component gap had no correlation with clinical outcomes. The valgus gap group in flexion showed poorer clinical outcomes than the severe varus, varus, and/or balanced gap groups. The slightly loose group of the medial component gap in extension showed lower 2011 KSS symptoms (P = 0.0352) and functional activities (P = 0.0085) than that in the tight group.

Conclusions: The valgus joint gap and medial looseness are negatively correlated with clinical outcomes, and residual varus joint gap and lateral laxity can be tolerated. Bone resection and soft-tissue release should be performed carefully to prevent medial looseness.