Metal or Modularity: Why Do Metal-Backed Tibias Have Inferior Outcomes to All-Polyethylene Tibial Components in Patients With Osteoarthritis.

Background: Biomechanical studies have suggested improved stress distribution in metal-backed (MB) compared to all-polyethylene (AP) tibias, but such potential benefits have not been realized clinically. The purpose of this investigation was to analyze the outcomes of AP components in patients with primary osteoarthritis and compare the results to those obtained with MB tibial components in total knee arthroplasty (TKA). Methods: We reviewed 11,653 patients undergoing primary TKA for osteoarthritis. There were 9999 (86%) MB (8470 modular and 1529 monoblock) and 1654 (14%) AP tibial components. All patients had at least 2 years of clinical follow-up with mean follow-up of 8 years (range, 2-30 years). Results: Mean survivorship for all primary TKAs at the 5-year, 10-year, 15-year, and 20-year time points was 97%, 92%, 86%, and 78%. AP tibial components were found to have improved survivorship when compared to modular and monoblock MB counterparts (P < .0001). Likewise, AP tibial components were found to have lower rates of tibial component loosening (P < .0001), tibial osteolysis, and component fracture. Furthermore, the AP group had improved survival rates in most age-groups except < 55 years where there was no difference. AP tibial components demonstrated improved survival for all body mass index (BMI) groups except in patients with a BMI <= 25 kg/m(2) where there was no difference. Conclusion: AP tibial components had significantly improved implant survival across all age-groups and most BMI categories in patients who underwent TKA for osteoarthritis. Given these outcomes, AP tibias are a reasonable option, regardless of patient age and BMI. (C) 2016 Published by Elsevier Inc.