PURPOSE: This study reports the relationship between posterior cruciate ligament (PCL) retention vs resection and soft tissue laxity and balance throughout flexion using a robotically controlled ligament tensioner. METHODS: 55 robotic-assisted TKAs (Total knee arthroplasty) were retrospectively reviewe. The robotic ligament tensioner collected laxity data both before and after PCL resection. Medial and lateral coronal laxity were compared before and after PCL resection at 10°, 45°, and 90° flexion. Gap opening was compared between pre-operative coronal hip-knee-ankle groups. RESULTS: Lateral laxity was greater after PCL resection at 60° (12.7 ± 2 vs 11.5 ± 3 mm), 75° (13.2 ± 2 vs 11.8 ± 3 mm), and 90° (13.7 ± 2 vs 12.1 ± 3 mm). Medial laxity was significantly greater after PCL resection at 90° (10.1 ± 2 vs 9 ± 2 mm). After PCL resection, laxity in valgus knees increased more compared to neutral/varus knees laterally at 30° (1.2 ± 1 vs 0.3 ± 1 mm), 45° (1.6 ± 1 vs 0.6 ± 1 mm), and 60° (2.1 ± 2 vs 1 ± 1 mm). A similar, but non-significant trend was observed at 90° (2.7 ± 2 vs 1.5 ± 1 mm, p = 0.09). CONCLUSION: PCL resection increases flexion laxity laterally by up to 1.6 mm and medially by 1.1 mm on average, with valgus knees increasing more than neutral/varus knees. The findings emphasize that surgeons should consider the interplay between PCL resection and coronal deformity when planning and executing TKA procedures.