Design and biomechanical investigation of a patient-specific total talar prosthesis for total talar replacement: A finite element analysis

BACKGROUND: Total talar replacement (TTR) is an emerging treatment for end-stage talar diseases, although concerns persist regarding ankle stability due to essential ligament transection. Further investigation is necessary regarding the biomechanical impact of patient-specific total talar prosthesis (TTP) on ankle stability and bone-implant mechanics. OBJECTIVE: The purpose of this study is designing a patient-specific TTP and assess its biomechanical performance on ankle stability and stress distribution under various loading conditions using finite element analysis. METHODS: A CT scan is used to create a 3D finite element model of the foot and ankle complex. The TTP made of A dual-material (UHMWPE talar body and titanium alloy cage) was created and fixed with five screws. Four loading conditions were simulated: inversion, eversion, dorsiflexion, and plantarflexion, with forces of 10 N, 50 N, 100 N, and 150 N. Talar tilt angles and von Mises stresses were examined for intact and implanted models. RESULTS: In comparison to the intact ankle, TTR significantly decreased the talar tilt angles in inversion (12.5%-16%), eversion (6.6%-14%), and dorsiflexion (33%-47%). On the other hand, plantarflexion produced a larger tilt (34%-44%). While bone stresses stayed below 5 MPa, maximum implant stresses ranged from 20 to 80 MPa. The validation of the model against cadaveric studies was reliable. CONCLUSION: The patient-specific TTP with screw fixation improves ankle stability in most loading directions, potentially compensating for ligament insufficiency. However, greater plantarflexion instability necessitates post-operative measures. These findings provide biomechanical evidence that fixation-enhanced TTP designs can improve therapeutic outcomes.