Use of All-polyethylene Tibial Components in Unicompartmental Knee Arthroplasty Increases the Risk of Early Failure

All-polyethylene (all-poly) tibial designs in primary total knee arthroplasty (TKA) have been reconsidered with excellent clinical outcomes, survivorship, and cost-effectiveness. However, whether all-poly tibial components provided comparable results to metal-backed modular components during unicompartmental knee arthroplasty (UKA) remains unclear. This study compared the clinical outcomes and prevalence of early failure between all-poly and metal-backed modular components in UKA. We retrospectively reviewed the records and radiographs of 101 consecutive UKAs. In total, 51 UKAs were performed using all-poly tibial components; 50 others used metal-backed modular components. Clinical and radiographic outcomes, adaptive bone remodeling assessed by radiographic bone density, and early failure prevalence rates were compared. Despite a lack of group differences in clinical and radiographic outcomes (p > 0.1 in all comparisons), adaptive bone remodeling at 2 years after surgery of all-poly UKAs was more progressive compared with metal-backed UKAs (1.2 in all-poly UKA group vs. 0.9 in metal-backed UKA group, p < 0.001). In addition, 6 of 51 all-poly UKAs failed within 2 years postoperatively, whereas no metal-backed UKAs failed (11% in all-poly UKA group vs. 0% in metal-backed UKA group, p = 0.027). All-poly tibial component use during UKA increased the risk of early failure, which may be due to a failure in tibial loading distribution.