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Background: As a new technology, three-dimensional (3D)-printed personalized talar prostheses are associated with different fixation methods for implanted prostheses, including fixing the subtalar joint and talus-navicular joint with screws and fixing the subtalar joint with screws only and fixation without screws. No biomechanical study has been conducted yet. we aimed to build a 3D finite element model to compare the biomechanical effects of different fixation methods.Methods: With 3D CT and MRI data of a volunteer's foot, Mimics research 19.0 and Geomagic wrap 2017 software were used to complete the geometric reconstruction of bone and cartilage, which was then input to NX12.0 software to build finite element models with different fixation methods. Finally, the models were imported into Abaqus 6.14 software for meshing and assigning material properties and the different biomechanical effects in three gait phases (heel-strike, midstance and push-off) were simulated. The pressure changes in the articular surface around the talus or the prosthesis, the micromotion of the talus and the prosthesis and ankle motion were measured.Results: The 3D finite element model created in this study has been verified to be consistent with previous studies.Finite element analysis of the biomechanical mechanism showed that screw fixation of the prosthesis in different gait phases mainly increased the pressure on the tibia-talus articular surface and decreased the pressure on the fused articular surface and joint micromotion, which hindered ankle motion. The indicator values were nearly the same in the models of fixation without screws and the healthy state.Conclusions: The biomechanical mechanism varies by fixation method according to the finite element analysis. Fixation of the prosthesis without screws yields values most similar to healthy values.Trial registrationThis study was approved by the institutional review board ethics committee of the Southwest Hospital Affiliated with the Army Medical University (No. ECFAH2006051)

Osteolysis at the tendon-bone interface can impair pullout strength during tendon-bone healing and lead to surgery failure, but the effects of clinical treatments are not satisfactory. Mesenchymal stem cell (MSC)-derived exosomes have been used as potent and feasible natural nanocarriers for drug delivery and have been proven to enhance tendon-bone healing strength, indicating that MSC-derived exosomes could be a promising therapeutic strategy. In this study, we explored Scleraxis (Scx) dynamically expressed in PDGFRα(+) bone marrow-derived mesenchymal stem cells (BMMSCs) during natural tendon-bone healing. Then, we investigated the role of PDGFRα(+) BMMSCs in tendon-bone healing after Scx overexpression as well as the underlying mechanisms. Our data demonstrated that Scx-overexpressing PDGFRα(+) BMMSCs (BMMSCScx) could efficiently inhibit peritunnel osteolysis and enhance tendon-bone healing strength by preventing osteoclastogenesis in an exosomes-dependent manner. Exosomal RNA-seq revealed that the abundance of a novel miRNA, miR-6924-5p, was highest among miRNAs. miR-6924-5p could directly inhibit osteoclast formation by binding to the 3'-untranslated regions (3'UTRs) of OCSTAMP and CXCL12. Inhibition of miR-6924-5p expression reversed the prevention of osteoclastogenic differentiation by BMMSCScx derived exosomes (BMMSCScx-exos). Local injection of BMMSCScx-exos or miR-6924-5p dramatically reduced osteoclast formation and improved tendon-bone healing strength. Furthermore, delivery of miR-6924-5p efficiently inhibited the osteoclastogenesis of human monocytes. In brief, our study demonstrates that BMMSCScx-exos or miR-6924-5p could serve as a potential therapy for the treatment of osteolysis during tendon-bone healing and improve the outcome.