Effect of Tibial Slope on Knee Mechanics for Posterior Cruciate Ligament Deficient Cruciate-retaining Total Knee Arthroplasty

Background Debate continues over optimal tibial slope in cruciate-retaining versus cruciate-sacrificing total knee arthroplasty (TKA). Medial congruent tibial bearings, allow either posterior cruciate ligament (PCL) retention or sacrifice, further complicate decision-making—particularly when bone cuts have been completed for a cruciate-retainin (CR)-TKA and the PCL becomes compromised. This study evaluated the effect of tibial slope on knee mechanics in PCL-deficient CR-TKA using a medial congruent bearing. Methods Fresh-frozen cadaveric knees underwent TKA with complete PCL resection and tested at tibial slopes of 0°, 3°, 5°, and 7° using robotic simulators. Passive laxity was assessed at 15°, 30°, 45°, 60°, and 90° of flexion using ±6 Nm internal-external torque, ±12 Nm varus-valgus torque, and ±100 N anterior-posterior and medial-lateral forces. Rapid-prototyped tibial bearings used to alter slope without additional bone cuts or rebalancing. Results Tibial slope had no significant effect (α = 0.05) on internal-external, varus-valgus, anterior-posterior, or medial-lateral laxity throughout flexion. Varus-valgus laxity decreased slightly with increasing slope, with a maximum difference of 1.4°. No consistent trend was observed in anterior posterior laxity. The joint shifted posteriorly on average of 2.2 mm per incremental slope increase. Lunge kinematics were not significantly affected. Conclusions Increasing tibial slope did not significantly affect V/V laxity or knee kinematics after PCL compromise. While greater slope shifted the dwell point posteriorly, overall laxity remained unchanged. These findings suggest that recutting the tibia to adjust posterior tibial slope may not be necessary when PCL compromise occurs during CR-TKA using a medial congruent bearing design, provided appropriate soft tissue balance is maintained.