The posterior tibial slope does not influence the flexion angle in posterior-stabilized mobile-bearing total knee arthroplasty

BACKGROUND: It remains uncertain whether an increase in the tibial slope leads to better flexion in posterior-stabilized (PS) total knee prostheses. PURPOSE: To compare the intra-operative flexion angle between standard and an additional 10° posterior slope inserts. PATIENTS AND METHODS: Between December 2014 and February 2015, 22 patients (25 knees) who underwent PS mobile-bearing primary total knee arthroplasty (TKA) were included. Flexion angles were measured using either standard or specially-made inserts. Differences in flexion angles between the two situations were analyzed to determine the relationship between changes in flexion angle and pre-operative flexion angle or body mass index (BMI), and between intra- and post-operative flexion angle. RESULTS: The difference between the average flexion angle of standard inserts and specially-made inserts was not statistically significant. Although the correlations between changes in flexion angle due to insert difference and flexion angle, pre-operative flexion angle or BMI were not significant, there was a positive correlation between intra-operative and post-operative flexion at 2 years. CONCLUSION: The results showed an additional posterior tibial slope by 10° did not affect the intra-operative flexion angle. Surgeons performing PS mobile-bearing TKA do not need to excessively slope the tibial bone cutting to improve the post-operative flexion angle. LEVEL OF EVIDENCE: I, Experimental study. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s42836-021-00085-5.