In vivo quantification of polyethylene wear in total ankle arthroplasty : a longitudinal study using weightbearing CT.

AIMS: In vivo assessment of polyethylene (PE) wear in total ankle arthroplasty (TAA) relies on approximation using 2D metal interspace height (2D-MIH) loss on weightbearing radiographs. Weightbearing CT (WBCT), combined with distance mapping, may improve quantification of PE wear over time using 3D metal interspace volume (3D-MIV) loss. This study aimed to assess 3D-MIV with successive WBCT scans. We hypothesized that WBCT based 3D-MIV would enable longitudinal quantification of PE wear and identify predictors. METHODS: This retrospective study included 29 ankles from 28 TAA patients (16 men, mean age 57.9 years (SD 10.5), BMI 26.3 kg/m² (SD 4.1)) who had WBCT scans at minimum two-year intervals. Patients aged below 18 years, and those with trauma or surgical procedures affecting ankle alignment between scans, were excluded. Demographic data, implant types, and clinical outcomes were extracted. 3D-MIV was measured after segmentation of individual bones and prosthetic components. Annualized approximated wear rates were calculated. Correlations and multivariate regression analyses were used to identify predictors. RESULTS: Mean follow-up between scans was 58.7 months (SD 17.9). Mean 3D-MIV decreased from 3.92 mL (SD 1.17) initially to 3.86 mL (SD 1.11) (p = 0.015). Yearly 3D-MIV loss was -11.34 mm³/year (SD 19.62). Correlations existed between 3D-MIV loss and coronal plane rotation (ρ = -0.58, p < 0.001), mediolateral translation (ρ = -0.52, p = 0.004, superoinferior translation (ρ = 0.56, p = 0.002) and BMI ≥ 27 kg/m² (p = 0.037). Multivariate regression identified coronal plane alignment (β = -3.66, 95% CI -7.31 to -0.01), p = 0.049) and mediolateral translation (β = -9.97, 95% CI -18.48 to -1.45), p = 0.024) as predictors of 3D-MIV loss. CONCLUSION: Using a WBCT-based approach, this study enabled longitudinal in vivo quantification of PE wear in TAA. Wear rates (~11.3 mm³/year) aligned with prior estimates, and the method correctly identified anticipated predictors of increased wear.