All-Polyethylene Tibial Component Lowers Risk of Revision: An Analysis of 27,657 Primary Total Knee Arthroplasties

Background and Purpose: Modularity of the tibial component in total knee arthroplasties (TKA) has many surgical benefits. It also reduces inventory related expenses but increases implant cost. The resulting locking mechanism micromotion that leads to non-articular microwear and has been an accepted consequence of modularity. The purpose of this study is to evaluate the risk of revision (all-cause and aseptic) of a monoblock all-polyethylene tibial component compared to a fixed bearing modular tibial construct with the same articular geometry while adjusting for potential confounders in a community based sample of primary TKAs. In addition, younger and older patient specific risk of revision was evaluated. Method: A retrospective analysis of prospectively collected data from a Total Joint Replacement Registry (TJRR) was conducted. All 27,657 primary TKAs enrolled between 2001 and 2010 performed for any diagnosis with the same implant from a single manufacturer were included in the study. Patient characteristics, as well as surgeon, hospital, procedure, and implant characteristics were compared by the main exposure of interest, i.e. the type of tibial prosthesis (monoblock all-polyethylene vs. metal-backed modular). The main endpoints of the study were all-cause and aseptic revisions only. Descriptive statistics and Cox-regression models were employed. Hazard ratios (HR) and 95% confidence intervals (CI) are provided. Results: The cohort consisted of 2,306 (8.3%) monoblock all-polyethylene tibial component TKAs and 25,351 (91.7%) modular metal-backed components. No gender, diagnosis or diabetic status differences were noted between the monoblock and modular cohorts. Patients with monoblock tibias were older (71.8 vs. 68.1 yrs, p < 0.001) and had a lower body mass index (30.1 vs. 31.6 kg/m2, p < 0.001). The median follow up time of the cohort was 2.9 years (interquartile range 1.2–5.1 years), during which 22 (0.95%) monoblock arthroplasties and 550 (2.17%) modular arthroplasties were revised. The all-cause revision rate/100 years of follow-up for monoblock and modular cohorts was 0.30 and 0.65, respectively. Their aseptic revision rate/100 of follow-up was 0.18 and 0.35, respectively. In adjusted overall models, the risk of all-cause revision (HR = 0.51, 95% CI 0.33–0.78, p = 0.002) and aseptic revision (HR = 0.59, 95% CI 0.29–1.19, p = 0.139) was lower in the monoblock cohort compared to the modular cohort. In adjusted models of patients 65 years and older, the risk of all-cause revision is 0.59 (95% CI 0.35–0.99, p = 0.045) in the monoblock cohort compared to modular cohort. In adjusted models of patients younger than 65 years old, the risk of all-cause revision (HR = 0.26, 95% CI 0.10–0.72, p = 0.010) and aseptic revision (HR = 0.27, 95% CI 0.11–0.65, p = 0.003) were lower in the monoblock compared to the modular cohort. Conclusion: For our entire cohort of 27,567 primary fixed bearing TKAs, monoblock all-polyethylene tibial components had a 49% lower risk of revision for all-causes and a 41% lower risk of aseptic revision when compared to modular metal-backed tibial constructs. For patients younger than 65 years old, the all-polyethylene component had a 74% lower risk of all-cause revision and a 73% lower risk of aseptic revisions when compared to modular tibial constructs.