Preserved posterior cruciate ligament contributed to knee sagittal stability, but not to rollback and deep knee flexion in cruciate-retaining total knee arthroplasty with a cruciate-substituting insert

Purpose: No previous report has compared the differences in postoperative functional outcomes between posterior cruciate ligament (PCL)-retaining (CR-) and PCL-sacrificing (CS-) total knee arthroplasty (TKA) with detailed intraoperative consideration of joint gap and balance. The purpose of this study was to evaluate the in vivo function of preserved PCL in TKA by comparing postoperative functional outcomes between CR- and CS-TKA with a cruciate-substituting insert (CS-insert), considering intraoperative influence factors, such as the posterior tibial slope, posterior condylar offset, joint gap, joint balance, and joint laxity. Methods: A total of 55 knees in 38 patients (27 knees from 18 patients in the CR group, and 28 knees from 20 patients in the CS group) were analyzed. Fluoroscopic evaluation under anesthesia in sagittal laxity, rollback amount, and the maximum flexion angles were compared between the groups. Results: There were no significant differences in intraoperative or postoperative all measurement values between the two groups, but the sagittal laxity was significantly smaller in the CR group [5.4% ± 4.5% (2.4 ± 2.1 mm)] than in the CS group [9.0 ± 3.8% (4.0 ± 1.7 mm)] (P ​< 0.01). There were no significant differences in the amount of rollback and postoperative maximum knee flexion angle between the groups. Conclusions: Preserved PCL in TKA with a CS-insert contributed to knee sagittal stability, but not to rollback and deep knee flexion.