Evaluating the validity of lightweight talar replacement designs: rational models and topologically optimized models

Abstract

Background Total talar replacement is normally stable and satisfactory. We studied a rational scaffold talus model for each size range created through topology optimization (TO) and comparatively evaluated a topologically optimized scaffold bone talus model using a finite element analysis (FEA). We hypothesized that the rational scaffold would be more effective for application to the actual model than the topologically optimized scaffold. Methods Size specification for the rational model was performed via TO and inner scaffold simplification. The load condition for worst-case selection reflected the peak point according to the ground reaction force tendency, and the load directions “plantar 10°” (P10), “dorsi 5°” (D5), and “dorsi 10°” (D10) were applied to select worst-case scenarios among the P10, D5, and D10 positions (total nine ranges) of respective size specifications. FEA was performed on each representative specification-standard model, reflecting a load of 5340 N. Among the small bone models selected as the worst-case, an arbitrary size was selected, and the validity of the standard model was evaluated. The standard model was applied to the rational structure during validity evaluation, and the TO model reflecting the internal structure derived by the TO of the arbitrary model was implemented. Result In worst-case selection, the highest peak von Mises stress (PVMS) was calculated from the minimum D5 model (532.11 MPa). Thereafter, FEA revealed peak von Mises stress levels of 218.01 MPa and 565.35 MPa in the rational and topologically optimized models, respectively, confirming that the rational model yielded lower peak von Mises stress. The weight of the minimum model was reduced from 1106 g to 965.4 g after weight reduction through rational scaffold application. Conclusion The rational inner-scaffold-design method is safer than topologically optimized scaffold design, and three types of rational scaffold, according to each size range, confirmed that all sizes of the talus within the anatomical dimension could be covered, which was a valid result in the total talar replacement design. Accordingly, we conclude that an implant design meeting the clinical design requirements, including patient customization, weight reduction, and mechanical stability, should be possible by applying a rational inner scaffold without performing TO design. The scaffold model weight was lower than that of the solid model, and the safety was also verified through FEA.

Ankle and Foot Arthroplasty and Prosthesis: A Review on the Current and Upcoming State of Designs and Manufacturing

“…Furthermore, the use of metal Additive Manufacturing allows for a more flexible prosthesis design, where a broader range of metals can be utilized to devise an optimal fit. With topology optimization, unnecessary weight from materials within the inner spaces of the implant can be eliminated for a lightweight design that improves comfort [46,50]. To address the development of osteosclerosis due to incongruent elastic modulus between prosthesis materials and bone, the use of ultra-high-molecular-weight polyethylene (UHMWP) on the articulation of the prosthesis with the tibia has been promoted as a potential substitute for wear reduction [51].…”

Design of a lightweight universal talus implant using topology optimization

“…In that study, a comparison was made between a topologically optimized scaffold and a rational scaffold of the inner structure of a talus replacement in three postures corresponding to peak gait cycle loads. The implant used was a recreation of a cadaveric talus, and the simulation excluded the fibula as well as the adjacent bones’ cartilages ( Kang et al, 2022 ). This exclusion likely decreases the accuracy of the resulting stress distributions, thereby affecting the optimized implant geometry and expected performance under more anatomically-accurate conditions.…”