Impact of Joint Laxity on 2-Year KOOS Outcomes of Posterior Stabilized Total Knee Arthroplasty

Abstract

Background: The objective of this study was to determine relationships between intra-operative posterior cruciate ligament (PCL) sacrificing posterior stabilized (PS) total knee arthroplasty (TKA) laxity measurements throughout flexion and patient outcomes at 2-years post-TKA; and to define clinically relevant laxity thresholds to optimize patient outcomes. Methods: In a single surgeon study, PCL sacrificing TKA using a robotics assisted platform with a digital joint tensioning device was performed in 115 knees in 115 patients. Final intra-operative joint laxity was recorded, and 2-year Knee Injury and Osteoarthritis Outcome Scores (KOOS) were obtained. A Simulated Annealing optimisation algorithm was used to identify medial and lateral laxity windows which maximized the 2-year KOOS pain score. Wilcox non-parametric tests were used to compare outcomes between groups. Results: Significant associations were found between intra-operative joint laxity and 2-year KOOS pain outcomes throughout flexion. Clinically relevant laxity windows were defined medially and laterally in mid-flexion and flexion for improved outcomes, whereas only a lateral laxity window could be defined in extension. When all laxity windows were satisfied a 14.5 KOOS point improvement was found (97.2 vs 77.8, p=0.0060) compared to knees which did not satisfy any window. Improvements in Activities of Daily Living (∆8.8, p = 0.0143), Sports (∆22.5, p = 0.0108), and Quality of Life (∆18.7, p = 0.0011) KOOS subscores were also found in knees which satisfied all windows versus 0 – 1 window. Conclusion: Intra-operative joint laxity is associated with post-operative outcomes in a PS knee design, wherein patients balanced within identified laxity targets reported improved outcomes over those that did not. Clinically significant thresholds were defined and were predominately found in mid-flexion and flexion for medial and lateral laxity. When target windows were combined further improved outcomes were identified.