Second-generation total ankle arthroplasties have encouraging medium-term results, but the wear of the joint materials is of concern. The aim of the current study was to examine and compare the size, shape, and concentration of polyethylene particles in synovial fluid with total ankle arthroplasties and established posterior-stabilized total knee arthroplasties. Synovial fluid was obtained from 15 patients with well-functioning total ankle arthroplasties and 11 patients with posterior-stabilized total knee arthroplasties at least 6 months after surgery. Polyethylene particles were isolated and analyzed using scanning electron microscopy. Particle size (equivalent circle diameter) in ankles was 0.81 ± 0.09 μm (mean ± standard error) and in knees was 0.78 ± 0.08 μm. Particle shape (aspect ratio) in ankles was 1.57 ± 0.04 and in knees was 2.30 ± 0.22. The particle concentration was 1.02 ± 0.43 × 107/mL in ankles and 1.13 ± 0.56 × 107/mL in knees, and the particle concentration and size in total ankle arthroplasties were similar to those in total knee arthroplasties. Total ankle arthroplasties generated significantly rounder particles than total knee arthroplasties. These data suggest that the long-term result of total ankle arthroplasty should be as good as posterior-stabilized total knee arthroplasties in terms of polyethylene wear and the prevalence of osteolysis.