Biomechanical evaluation of load transfer in Talus focal resurfacing implant: experimental and finite element models

Osteochondral lesions (OTLs) are common injuries in ankle sprains, occurring in up to 70 % of patients. Recovery options are limited due to the talus bone's poor vascularization. This study aimed to develop a computational model of an ankle joint to evaluate cartilage stress in the presence of an OTL and assess the biomechanical effectiveness of a focal resurfacing prosthesis in reducing joint stress.

Both in silico and physical model models were developed based on a previous case study involving a patient with a medial OTL in the right ankle. A 10 mm diameter focal resurfacing prosthesis was tested in two positions: proud (+0.5 mm) and recessed (-0.5 mm), as recommended in clinical guidelines. Cartilage stress and trabecular bone strain in the talus were evaluated. The in vitro model, produced via additive manufacturing and instrumented with strain gauges, was used to validate the finite element (FE) model by comparing measured and simulated strains.

The FE model showed strong agreement with experimental data, with a correlation coefficient of 0.88. Both the lesion and prosthesis placement influenced talar cartilage stress. The OTL increased stress by approximately 23 % near the lesion site and 8 % in more distal regions. The highest cartilage stress (7.20 MPa) occurred with the prosthesis in the recessed position. Prosthesis positioning significantly affected cartilage stress distribution (p < 0.001).

While fixation of the focal prosthesis remains challenging, placing it slightly proud can help reduce stress on talar cartilage. However, excessive proud positioning increases stress on tibial cartilage and should be avoided. Proper prosthesis placement is critical for optimal stress reduction. Furthermore, fixation in the talus reduces trabecular bone strain, potentially mitigating bone loss and enhancing implant stability.