Compliant buffer layer achieves native-like cartilage stress in talar prosthesis: a finite element analysis study.

Background: Avascular necrosis (AVN) of the talus presents considerable clinical challenges and is frequently associated with poor treatment outcomes. While 3D-printed customized talar prosthesis has shown promising potential in total talar replacement (TTR), current materials create a hard-soft mismatch with native cartilage, increasing local stress, accelerating wear, and causing complications. The objective of this study was to identify the most suitable combination of buffering layer material and thickness for talar prosthesis.

Methods: This study employed dynamic biplane radiography (DBR) integrated with finite element analysis (FEA) to systematically evaluate how prosthetic material selection and buffering layer thickness affect periprosthetic cartilage biomechanics. We investigated the effects of mechanical stress on prosthesis adjacent cartilage (PAC) in 8 participants using 9 commonly used prosthetic materials with varying elastic moduli, combined with different cushioning layer thicknesses, across 5 gait phases. Statistical analyses included repeated measures ANOVA, Tukey's HSD post hoc tests, and a linear mixed-effects model to assess the impact of material properties and thickness on PAC stress.

Results: Compliant buffering layers composed of 3 mm polycarbonate urethane (PCU) effectively restored cartilage stress distributions to physiologically native levels during key phases of gait. We also found that soft prosthetic materials significantly reduce PAC stress compared to conventional hard materials. All hard prosthesis (Al2O3, Ti-6Al-4 V, CoCrMo, PyC and PEEK) showed higher stress than native group (p < 0.01). Notably, a buffering layer thickness of 1.5 mm with an elastic modulus below 43.32 MPa, or a 3 mm layer with an elastic modulus below 96.94 MPa, significantly reduced PAC stress to levels comparable to the native condition.

Conclusions: Our results indicate that when the prosthesis incorporates a 1.5-mm buffering layer with an elastic modulus below 43.32 MPa, or a 3 mm layer with an elastic modulus below 96.94 MPa, the peak stress in the PAC closely approximates that of the native condition. Furthermore, our findings indicate that a 3 mm PCU layer shows potential as a buffering component for talar prostheses. These findings provide preliminary insights for optimizing the material selection and structural design of talar prosthesis in TTR.