The degree of change in PCO was greater in the lateral condyle than in the medial condyle (3.1 ± 2.5 mm and −0.5 ± 2.8 mm, respectively). Postoperative medial and lateral tibial slopes were 1.4° ± 1.8 and 1.4° ± 2.0, respectively. The mean degree of postoperative knee flexion was 125°. Analysis with interaction terms and covariate adjustment demonstrated that medial PCO and tibial slope were significantly related to knee flexion with interactive effect (P = 0.011). In cases with <3° posterior tibial slope, the postoperative PCO was positively correlated to the degree of knee flexion angle. However, in cases with >3° tibial slope, PCO was negatively correlated to knee flexion.